Method for working billets of metals and alloys
A multiple stage method for plastic working of a blank, comprises applying a torsional loading to the blank at a first stage in multiple steps at loading conditions selected to effect microstructure transformation; and applying a tensile or compression loading at a second stage subsequent to the torsional loading stage. An article, comprises a hollow blank with a hollow core emplaced within the blank and expanded by pressurized fluid contained within the core interior and a sheath encompassing the blank in a blank to sheath contact along a blank lateral surface that prevents the sheath and blank from displacement relative to each other.
[0001] The invention relates to metallurgy, namely to thermomechanical working of billets with a cast coarse-grained laminated microstructure, in particular, billets of titanium and its alloys, in order to obtain a definite microstructure therein.
[0002] The invention can be used for obtaining forged members and preliminarily prepared blanks for manufacturing products intended for operation in various fields of industry including airspace industry.
[0003] The achievement of high technological and operational characteristics in many alloys, as a rule, requires obtaining a microcrystalline structure of a definite type, on the one hand, and its uniformity on the other hand. In this case, a microcrystalline structure of a microduplex type with a mean grain size of d=1.0-10.0 microns is optimal from the point of view of low values of flow stress and maximum plasticity. At the same time, a combination of good plasticity, high impact resistance and long-time strength can be obtained having a microstructure of the basketry type. It is well known that the basic method for obtaining such a microstructure is heat treatment of a material, which in a starting condition has a microcrystalline structure of the microduplex type. Thus, urgency of the problem of obtaining maximum strength characteristics of the material in various articles is directly connected to the problem of obtaining high technological characteristics of the billet material.
[0004] At present, quite a number of technological methods are known which allow one to obtain a microcrystalline structure both in small specimens and in large-size billets. The analysis has shown that all these methods feature the same physical nature: an increase of the intrinsic energy of the specimens being deformed due to hardening as a result of an intensive plastic deformation and the transfer to a stable state due to the weakening processes such as recovery, re-crystallization, etc.
[0005] Known in the art is a method for working of metallic materials in which use is made of intensive plastic deformation when deforming by compression with torsion of thin plates between two flat hammers to obtain a microstructure with a mean grain size of 50 nm. This method of billet working is known as “deformation on the Bridgeman anvil”. The intensive shear deformation of billets made of hardly deformable materials, which is possible as a result of raising their plasticity during the torsion, is achieved by creation in the billet of a stress state close to quasi-hydrostatic compression.
[0006] The disadvantage of this method consists in limited possibilities of obtaining large-size billets. An increase of the billet size is accompanied by an increase of heterogeneity of distribution of the accumulated deformation through the cross section resulting in high nonuniformity of distribution of the microstructure in the billet. In view of this drawback, the given method is used, as a rule, under laboratory conditions.
[0007] Also known in the art is a method for working of materials, which is based on shear deformation under conditions of quasi-hydrostatic pressure named “Equal-channel angular pressing”. In contrast to the above-mentioned method, the intensive shear deformation is accumulated as a result of multiple pressing mainly of axially symmetric and long-length billets in a channel of a constant cross-section having a bend. The angle of bending is equal to or less than 90°. Depending on the value of the frictional forces between the billet and the tool, the method allows pressing with a counter-pressure.
[0008] The basic advantage of the method of “Equal-channel pressing” in comparison with the “deformation on the Bridgeman anvil” is that it can be used for preparation of a microstructure in the billets having a large volume.
[0009] This method is used when processing metal billets and alloys to obtain therein a given microstructure at low temperatures. When processing billets of hardly deformable material, in particular titanium and its alloys at a high temperature, a protective lubricant layer must be provided, which is still a problem.
[0010] Thus, the known methods are intended for obtaining a given microstructure in small specimens under laboratory conditions.
[0011] Besides, the known methods do not allow one to obtain a regulated non-uniform structure across the billet section.
[0012] Also known in the art is a method for working of billets of hardly deformable materials including provision of a microcrystalline structure in the billet, which is chosen as a relevant prior art.
[0013] The method includes initial hot deformation of billets by compression at a temperature within 450 F (232.2° C.) but not below its normal re-crystallization and subsequent hot die forging at a temperature of 350 F (176.7° C.), but is not below the re-crystallization temperature of the processed alloy.
[0014] The formation of microcrystalline structure in the billets using such a working is attained due to the development of re-crystallization processes after the hot hardening during hot pressure working of billets.
[0015] One of the main advantages of the method in question is a possibility of effective working of semi-finished components of a medium dimension, as well as products of a complex shape.
[0016] At the same time, the method has some disadvantages.
[0017] It is known that the chosen scheme of working of billets by compression is characterized by a non-uniform deformation of the material through the cross section, which results in formation of a forging cross and dead spaces directly in the area of contact of the die tool with the billet. An increase of the size of the processed billet results in irregular distribution of deformation throughout the volume of billets leading to appearance of an uncontrollable gradient on the grain size in the volume of the billets. In this connection, there is practically no possibility of obtaining a required microstructure in the billet cross section.
[0018] There is practically no possibility of getting a regulated microstructure characterized by the different size of the grains through the billet cross section.
[0019] Hardly deformable materials, especially titanium alloys have rather a low value of heat conductivity, which has the greatest effect on the rate of heating and cooling. This effect is especially noticeable at an increase of the size of processed billet. The need in the operation of compression at the first step of working of the billets introduces restrictions on the ratio of the billet size by height to the cross size, because of the loss of the billet stability during the compression. Therefore, an increase in the billet weight results in an increase of its cross-sectional area and duration of its heating during the deformation. By increasing the heating rate, it is possible to reduce the time necessary for warming up the billets, however in this case the temperature field gradient in the cross-sectional area is also increased resulting in breaking the uniformity of distribution of the grain size throughout the billet volume.
[0020] The experiments have shown that the higher the deformation temperature and the longer time of heating the billet under hot deformation, the larger the grain and this, alongside with the structure non-uniformity of, significantly limits the application of this method when working large-size billets.
[0021] The method under consideration provides the use of compression under isothermal conditions and, as a result, application of a heated stamping tool. The experience has shown that the weight of the stamping tool exceeds the weight of the processed billet by dozens of times. Therefore, at increase of the dimensions of the processed billet, alongside with the growth of the expenses on the material and stamping tools manufacture, the cost of its heating also rises up which is in many times higher than the cost of heating the processed billet.
[0022] The increase of the sizes of processed billet also entails an increase of required forces of the press equipment. It is well known that a two-fold change of the cross size of the processed billet results in a change of the capacity of the required equipment by a factor of four.
[0023] Thus, the above method for working of the billets can be attributed to high-energy processes. In this case the power consumption grows proportionally to the growth of the processed billet weight.
[0024] Hence, there is a need for a method to treat billets of metals and alloys to obtain a microcrystalline structure that is uniform or regulated in the cross-sectional area.
BRIEF DESCRIPTION OF THE INVENTION[0025] The invention provides a multiple stage method for plastic working of a blank, comprising: applying a torsional loading to the blank at a first stage in multiple steps at loading conditions selected to effect microstructure transformation; and applying a tensile or compression loading at a second stage subsequent to the torsional loading stage.
[0026] In an embodiment, the invention comprises a multiple stage method for plastic working of a titanium blank, comprising: working a titanium blank by applying a torsional loading to the blank at a first stage in multiple steps at loading conditions selected to effect microstructure transformation; and applying a tensile or compression loading at a second stage subsequent to the torsional loading stage, wherein the working is at a deformation ration and under temperature-and-rate conditions selected to effect dynamic recrystallization in beta-phase; and heat treating to effect phase transformation.
[0027] In another embodiment, a multiple stage method for plastic working of a blank, comprises working the blank by applying a torsional loading to the blank at a first stage in multiple steps at loading conditions selected to effect microstructure transformation; and applying a tensile or compression loading at a second stage subsequent to the torsional loading stage, wherein the blank is deformed by working in a uniaxial tension sheath of a material, capable of undergoing superplastic deformation, wherein the sheath is in contact along the lateral surface of the blank to prevent displacement between the sheath and blank during working.
[0028] In still another embodiment, a multiple stage method for plastic working of a blank, comprises deforming by working the blank by applying a torsional loading to the blank at a first stage in multiple steps at loading conditions selected to effect microstructure transformation; and applying a tensile or compression loading at a second stage subsequent to the torsional loading stage, wherein a deforming force is imparted to the blank through an inseparable joint with a tool.
[0029] In still another embodiment, a method for plastic working of blanks, comprises determining deformation accumulated in working a blank; determining depth of a layer of the blank being wrought; determining the plasticity reserve of the blank being wrought; and further applying a number of deformation steps to the blank according to the determined accumulated deformation, layer depth and plasticity reserve.
[0030] Additionally, the invention relates to an article, comprising a hollow blank with a hollow core emplaced within the blank and expanded by pressurized fluid contained within the core interior and a sheath encompassing the blank in a blank to sheath contact along a blank lateral surface that prevents the sheath and blank from displacement relative to each other.
BRIEF DESCRIPTION OF THE DRAWINGS[0031] FIG. 1. A schematic diagram of the apparatus for realization of the method;
[0032] FIG. 2. A general view of the apparatus;
[0033] FIG. 3. A general view of the processed billet;
[0034] FIG. 4. An initial microstructure of the billet of alloy VT9;
[0035] FIG. 5a. A diagram of two-step treatment of a long-length billet of alloy VT9;
[0036] FIG. 5b. A diagram of the corresponding loading paths;
[0037] FIG. 6. An appearance of the processed long-length billet of alloy VT9 after the first step;
[0038] FIG. 7. A microstructure in processed long-length to billet of alloy VT9 after the second step;
[0039] FIG. 8a. A diagram of two-step treatment of short-length billet of alloy VT9;
[0040] FIG. 8b. A diagram of the corresponding loading paths;
[0041] FIG. 9. An initial microstructure of the billet of alloy VT9;
[0042] FIG. 10a. A diagram of a single-step working of a long-length billet of alloy VT6;
[0043] FIG. 10b. A diagram of the corresponding loading paths;
[0044] FIG. 11. An appearance of the processed billet of alloy VT6;
[0045] FIG. 12. A microstructure of the processed billet of alloy VT6;
[0046] FIG. 13a. A diagram two-step treatment of a long-length billet in three passes at the first step and intermediate heat treatment between them aimed at development of phase transformations;
[0047] FIG. 13b. A diagram of the corresponding loading paths;
[0048] FIG. 14a. A diagram of two-step treatment of a long-length billet with three passes at the first step and intermediate heat treatment between them aimed at development of static re-crystallization and heat treatment aimed at development of phase transformations;
[0049] FIG. 14b. A diagram of the corresponding loading paths;
[0050] FIG. 15a. A diagram of single-step working of a long-length billet with three passes at the first step and intermediate heat treatment between them aimed at development of phase transformations;
[0051] FIG. 15b. A diagram of the corresponding loading paths;
[0052] FIG. 16a. A diagram of two-step treatment of a long-length billet in three passes at the first step and intermediate treatment between them aimed at development of phase transformations;
[0053] FIG. 16b. A diagram of the corresponding loading paths;
[0054] FIG. 17. An initial microstructure of the billet of alloy VT8;
[0055] FIG. 18a. A diagram of two-step treatment of a long-length billet of alloy VT8 in two passes at the first step and intermediate heat treatment between the steps aimed at development of phase transformations;
[0056] FIG. 18b. A diagram of the corresponding loading paths;
[0057] FIG. 19. A microstructure of the billet of alloy VT8 after the working;
[0058] FIG. 20. A macrostructure of the large-size billet of alloy VT6 in an initial condition;
[0059] FIG. 21. A microstructure of the large-size billet of alloy VT6 in an initial condition;
[0060] FIG. 22a. A diagram of working the large-size billet of alloy VT6 including preliminary and main two-step treatment of a long-length billet with one pass at the first step.
[0061] FIG. 22a. A diagram of the corresponding loading paths;
[0062] FIG. 23. An appearance of the large-size billet of alloy VT6 after the working.
[0063] FIG. 24. A macrostructure of the large-size billet of alloy VT6 after the working;
[0064] FIG. 25. A microstructure of the large-size billet of alloy VT6 after the working;
[0065] FIG. 26. A diagram of joint working of a cylindrical billet.
[0066] FIG. 27. A diagram of separate working a tubular billet with an internal non-formable core.
[0067] FIG. 28. A diagram of working a tubular billet with an internal non-formable core using movement of the billet.
[0068] FIG. 29. A diagram of joint working a tubular billet in a sheath with a hollow deformable core using movement of the billet sheath and the core.
[0069] FIG. 30. A diagram of working the billet between the sheath and the core with a cylindrical contact surface.
[0070] FIG. 31. A diagram of working the billet between the sheath and the core with conical contact surface.
DETAILED DESCRIPTION OF THE INVENTION[0071] The invention provides a uniform and regulated cross sectional microstructure. The invention can increase efficiency of microstructure reduction to obtain a grain size of 5.0 to 10.0 microns in lower and large size billets. In this application, large size billets are those weighing more than 200 kg. The invention can reduce power consumption with the processing of large size billets and decrease labor consumption throughout a treatment process.
[0072] The invention provides a method for working billets of metals and alloys by plastic deformation to an extent and under temperature and rate conditions to provide microstructure reduction. In the method, a billet or its regulated part can be worked in one or several steps by applying a primary torsion loading and applying a tension or compression next step or steps. Or, the billet can be worked in a succession of steps of alternating torsion loading and tension or compression next steps. The torsion loading step can be effected in several passes or steps with deformation and/or heat treatment between the passes and/or steps. Loading conditions in the passes or steps can be selected to accomplish microstructure transformation.
[0073] In this specification, the recitation of one element, feature or step shall mean one or more of the elements, features or steps. A “blank” is an unfinished metal or alloy such as a billet. The term “titanium” includes titanium metal, alloy, composite and other titanium-containing compositions
[0074] Some of the aspects or embodiments of the invention include:
[0075] carrying out the working in several steps wherein at the first step, microstructure is transformed according to conditions of deformation and superplasticity;
[0076] selecting a number of steps and types of loading according to an initial starting configuration and grain sized and s desired final billet configuration;
[0077] selecting a number of steps and loading types according to billet cross section grain size distribution; in the instance of titanium and titanium alloy billets,
[0078] in the instance of titanium and titanium alloy billets, selecting a deformation extent, temperature and rate conditions per pass so as to provide dynamic re-crystallization in a &bgr;-phase and effecting a heat treatment between passes to provide phase transformations;
[0079] in the instance of titanium and titanium alloy billets, selecting extent, temperature-and-rate conditions per pass so as to provide static re-crystallization in a &bgr;-phase and effecting re-crystallization annealing heat treatment between the passes to provide phase transformations;
[0080] in the instance of (&agr;+&bgr;) titanium alloys, deforming the billet at a constant temperature not exceeding [Tac3−(20+30)]° C. in at least one pass;
[0081] in the instance of an &agr;- or pseudo &agr;-titanium alloy billet, deforming the billet in at least one pass at a constant temperature in a temperature range of TAc3+TAr3 of the alloy temperature;
[0082] heat treating by cooling the billet at a regulated rate to provide direct phase transformation by the diffusive mechanism;
[0083] selecting a cooling rate not higher than that corresponding to the martensite transformation in the &bgr;-phase and not lower than the rate corresponding to the greatest intensity of formation of annealing twins in the &agr;-phase;
[0084] cooling to a temperature of the next pass;
[0085] selecting a temperature for the next pass that is lower than the temperature of the preceding pass;
[0086] selecting a temperature for the next pass that is equal to the temperature of the preceding pass;
[0087] cooling below the temperature of the next pass followed by heating to the next pass temperature;
[0088] cooling at room temperature followed by heating to the next pass temperature;
[0089] after a pass, heating the billet to a temperature above the temperature of the preceding pass and subsequently cooling to a temperature of the next pass;
[0090] working the billet at a variable temperature in a pass;
[0091] in the instance of titanium and titanium alloy billets with an original cast structure, preconditioning the billet to provide dynamic re-crystallization in the &bgr;-phase and a heat treating to provide reverse phase transformation;
[0092] in the instance of titanium and titanium alloy billets with an original cast structure, preconditioning the billet to provide dynamic re-crystallization in the &agr;-phase and a heat treating to provide reverse phase transformation in the first treatment step;
[0093] a subsequent step deformation temperature is selected below a deformation temperature at a first step;
[0094] selecting a number of passes and a degree of accumulated deformation for a step according to a depth of the layer being treated and the plasticity resource of the processed material;
[0095] deforming in two steps, wherein first step accumulated deformation is selected so as to provide a volume microstructure reduction according to the relation: 1 V 1 ≥ V 0 σ 2 ( σ 1 + σ 2 ) , ( 1 )
[0096] where:
[0097] Vo is the volume of the whole billet;
[0098] V1 is the volume of the transformed part of the billet,
[0099] &sgr;1 is the flow stress of the material with a microcrystalline structure;
[0100] &sgr;2 is the flow stress of the material in the starting billet,
[0101] and wherein a second step temperature is selected below the first step deformation temperature;
[0102] deforming in three steps, wherein, the third step comprises shaping the billet using axial loading components;
[0103] in the instance where the starting material is an axially symmetric billet in the form of a rod having less than a preset grain size, shaping the billet using uniaxial tension;
[0104] in the instance where the starting material is an axially symmetric billet in the form of a washer having less than a preset grain size, shaping the billet using uniaxial compression;
[0105] deforming the billet in a first step by combined torsion and compression;
[0106] deforming the billet in a first step by combined torsion and tension;
[0107] deforming the billet in a first step by alternating torsion and combined torsion and compression;
[0108] deforming the billet in a first step by torsion and alternating combined axial loading and torsion;
[0109] deforming the billet in a first step by axial loading and alternating combined axial loading and torsion;
[0110] deforming the billet in first step comprising monotonic two-component loading wherein the ratio between the axial component of the deforming force and the torsion component is not in excess of 0.2.
[0111] deforming the billet in a second step by combined torsion and compression;
[0112] deforming the billet in a second step by combined torsion and tension;
[0113] deforming the billet in a uniaxial tension sheath of a material, capable of undergoing superplastic deformation, wherein the sheath is in contact along the lateral surface of the billet to prevent displacement between the sheath and billet during working;
[0114] in the instance of a hollow billet, installing a core within the billet prior to deformation;
[0115] in the instance of a hollow billet, installing a core within the billet and working the billet by multicomponent loading wherein the core is made of a material that at the temperature and rate conditions of working results in superplasticity working of the billet;
[0116] in the instance of a hollow billet and core, deforming the billet in a uniaxial tension sheath of a material, capable of undergoing superplastic deformation, wherein the sheath is in contact along the lateral surface of the billet to prevent displacement between the sheath and billet during working;
[0117] in the instance of a hollow billet and core, the core is hollow;
[0118] in the instance of a hollow billet and core, the core is solid;
[0119] in the instance of a hollow billet and core, the billet and core are deformed jointly;
[0120] in the instance of a hollow billet and core, the billet and core are deformed separately;
[0121] in the instance of a hollow billet and core, the billet is expanded by pressure-feeding a working fluid into the core internal space;
[0122] in the instance of a hollow billet and core, the billet includes a material that has viscous-fluid properties during the billet working;
[0123] in the instance of a hollow billet and core, after working, the billet is expanded by pressure-feeding of a working fluid into the core;
[0124] permanently expanding a thin-walled billet to provide contact between the billet and a sheath on the lateral surface of the billet that prevents relative displacement of the billet and sheath in the process of working;
[0125] in the instance of working a billet in a sheath, the sheath comprises a material that undergoes superplastic deformation under the selected temperature-and-rate conditions of working;
[0126] in the instance of a hollow billet and core within a sheath, the core comprises a material that resists deformation to provide a uniform billet and core contact in the process of working of the billet by displacing the sheath relative to the core;
[0127] providing a uniform contact over the whole surface of the billet and the core preventing mutual displacement of the billet, sheaths and core in the process of working, while the billet is deformed by displacing the sheath relative to the core;
[0128] in the instance of a hollow billet and core within a sheath, the billet and the contact surfaces of the sheath and core have a conical shape;
[0129] in the instance of a hollow billet and solid core within a sheath, contact among the hollow billet, sheath and core is provided at the expense of thermal tightening;
[0130] in the instance of a hollow billet and solid core within a sheath, contact among the hollow billet, sheath and core is provided by brazing, in which case the initial thickness of layer &Dgr; is selected from the condition 50.0 &mgr;m <&Dgr;<200.0 &mgr;m;
[0131] working lamellae by placing the lamellae between a sheath and a core to provide contact over the whole lamellae surface, preliminarily deforming the lamellae and deforming by displacing the sheath and the core relative to each other;
[0132] working lamellae by placing the lamellae between a conical sheath and core. wherein preliminarily deforming the lamellae is effected during assembly of the lamellae, sheath and core;
[0133] working a billet in the form of a bar by uniformly applying a deforming force to an end face surface over an area having a radius r equal to 0.7<r<R, where R is the radius of the billet;
[0134] working a billet by applying a deforming force transmitted through a permanent joint between the billet and a tool;
[0135] working a billet by applying a deforming force transmitted through a permanent joint made by fusion welding between the billet and a tool;
[0136] working a billet by applying a deforming force transmitted through a permanent joint made by solid-phase welding between the billet and a tool;
[0137] working a billet by applying a deforming force transmitted through a permanent joint made by brazing, with a braze material selected with a melting point higher than the temperature of working of the billet and a layer thickness selected from the condition 50.0 &mgr;m<&Dgr;<200.0 &mgr;m;
[0138] working a billet by applying a deforming force transmitted through applied to the being processed is transferred through a plug connection with the tool.
[0139] effecting microstructure reduction according to a soft loading scheme or combination of a soft loading scheme and a semi-hard or hard scheme to provide accumulated deformation thereby decreasing re-crystallization temperature, increase of re-crystallization volume or speed of a re-crystallization process at a normal temperature. When working large-size billets, shear deformation is used efficiently since only the surface layers are sheared and not the whole billet.
[0140] effecting microstructure reduction according to a soft loading scheme to provide grain reduction:
[0141] effecting microstructure reduction according to a soft loading scheme only at the expense of the dynamic re-crystallization;
[0142] effecting microstructure reduction according to a soft loading scheme to provide deformation and to develop static re-crystallization during heat treatment after the deformation;
[0143] effecting microstructure reduction according to a soft loading scheme to provide deformation and to develop dynamic re-crystallization in one phase and heat treating to provide direct phase transformation; and
[0144] effecting microstructure reduction according to a soft loading scheme to provide deformation and to develop static re-crystallization during the heat treating after the deformation and a second cycle of heat treating to provide reverse phase transformation.
[0145] The choice of any alternative depends on the physical properties of the processed material, the structure in the starting billet, temperature-and-rate conditions of the deformation, as well as preset or maximally allowable extent of deformation.
[0146] All the above conditions are taken into account when determining the number of passes in the working steps. For example, when a material with low plastic properties is subjected to the working, the required working of the layer is obtained due to the use of multipass working and re-crystallization annealing between the passes.
[0147] The development of the process of plastic deformation under conditions of progressing shear deformation due to torsion stimulates formation in the material of stable dislocation nodes, that itself or in a combination with a subsequent heat treatment, provides controlled development either dynamic or static re-crystallization or in a combination with phase transformations accelerates the processes of transformation of a coarse-grained or rough laminated microstructure into a globular or microduplex structure in the surface layers.
[0148] At the second step, axial loading by tension or compression creates a uniform stress-strain state in the billet cross section. High sensitivity of the flow stress to the deformation rate, typical for materials with superplastic properties in the surface layers, allows one to reduce the material to fine grains during the subsequent deformation of the central part of the billet, providing uniform deformation in the cross-sectional area without formation of a neck at tension or without formation a forging cross at the compression and premature destruction of the whole billet.
[0149] The use of torsion at the first step and single-step working makes it possible to obtain a structure non-uniform through the cross-section due to the transformation of the microstructure in the surface layers of the billet. The working in two or more steps allows one to obtain a microstructure uniform through the whole volume.
[0150] When working billets in two or more steps a recommended condition at the first step is to obtain a microstructure providing at the next steps a proper progress in the treated layer of deformation under the superplasticity conditions.
[0151] The proposed mechanical scheme of loading allows one to increase the dimensions of the processed billet by increasing their length, because at the second step it is possible to use tension or tension with torsion. The possibility of increasing the weight of the billets by increasing the length without changing the cross section provides uniform warming of the billets in a shorter time, and this allows one to obtain a microcrystalline structure with a mean grain size of 10.0 to 15.0 microns in billets having a weight of 200 kg and more.
[0152] With a decrease of the cross section of the processed billet, it is possible to obtain a mean grain size considerably less than 10.0-15.0 microns.
[0153] The decrease of specific power consumption with an increase of the weight of the processed billet is achieved due to the fact that the torsional loading scheme requires lower power consumption. In particular, it drops down due to the absence of deforming tools in the working zone. In this case, the larger the dimension of the processed billets, the higher the efficiency of the proposed method according to this criterion.
[0154] When working the billets, the use of torsion as the basic loading component allows one to increase the speed of the process by an order of magnitude while maintaining the rate of deformation of the material as a controlled, constant and optimal parameter throughout the billet volume compared, for example, with compression. For example, when preparing a structure in a billet 100 mm in diameter and 250 mm long and made of titanium alloy BT6 having a cast structure in the initial condition at a deformation rate of 10−3 s−1 on the lateral surface, the deformation e=3.6 was accumulated for 12-15 minutes. In so doing 80% of the billet volume has undergone transformation into a microduplex structure. A similar value of the accumulated deformation at compression of the ingot of same size, which is necessary for complete transformations, is gained for 4-7 working shifts and is associated with a necessity of performing intermediate heating.
[0155] The efficiency of the method is confirmed by such a criterion as the absence of the deforming tool in the working zone excluding appearance of friction forces and expenses associated with their overcoming whose amount in the known solutions grows with an increase of the dimension of the billet being worked.
[0156] Besides, the maintenance of the cross size and the increase of the length of the billet reduces the time of its heating to the operating temperature and makes the time of heating practically independent on the dimensions of the processed billet.
[0157] The number of steps and type of loading are selected taking into account the configuration of the starting and final billet and the size of grains in the starting billet. The shape and the geometric dimension of the billets, as well as the initial microstructure determine the conditions of the deformation-and-heat treatment of the billets to obtain therein a microcrystalline structure, as well as the type of loading the billet. For example, hollow billets are preferably processed by torsion. When working the long-length billets, at the first step use is made of torsion or torsion with tension and at the subsequent steps—only the tension. When working the short-length billets, at the first step use is made of torsion or torsion with compression, and at the subsequent step—only the compression. When a billet with a low-ductility structure is to be worked, this billet should be deformed in a sheath.
[0158] The amount of steps and type of loading are selected taking into account a given distribution of the grain size in the billet cross section. When it is necessary to perform only surface treatment of the billets, it is expedient to use the torsion only. A preset grain size in the cross sections of the processed billet is obtained due to a preset value of the deformation accumulated during the torsion, which is determined by the torsion angle, the rate and a possibility of reverse torsion.
[0159] When working billets of titanium and its alloys, the extent and temperature-and-rate conditions of deformation per pass should provide dynamic re-crystallization only in the &bgr;-phase.
[0160] The presence of many equivalent slip systems in the volume-centered cubic lattice of high-temperature allotropic modification of the &bgr;-phase determines the development of a plastic flow of the material due to multiple slip. A comparatively low value of the stacking fault energy for the &bgr;-phase of E˜20 erg/MM2 is a reason of appearance stable, flat and dimensional dislocation clusters transforming during the deformation into a cellular microstructure with a cell size of 1-2 microns, with a wall thickness of 0.6-0.7 micron and consisting of volumetric coils with high density of the dislocation at the boundary and low density of dislocations inside the cells. The further deformation results in reduction of the thickness of the cell boundaries and an increase of their curvature. On this background, we have also an increase of the crystallographic disorientation between the adjacent cells. It is well known that a similar evolution of the dislocation structure precedes a beginning of the dynamic re-crystallization, which results in formation of high-angle intergranular boundaries. The re-crystallization in the &bgr;-phase apparently occurs at smaller extents of deformation leading to a decrease of the total deformation necessary for reduction of the structure. The heat treatment performed between the steps and aimed at provision of direct phase transformation by the diffusion mechanism, for example, when cooling the billet at a controlled rate, will result in separation of the &agr;-phase in the triple joints of the newly formed intergranular boundaries of the &bgr;-phase. The primary separation of the &agr;-phase at the triple joints is caused by high diffusivity at the intergranular (&bgr;-&bgr;) boundary of a general type compared to the special coherent interphase (&bgr;-&agr;) boundary, as well as their greater extent per unit volume due to a small grain size. On the other hand, the high level of energy of the intergranular boundary compared to the interphase one is a reason of appearance of a gradient of chemical potential which determines the directed diffusive mass transfer. Thus, both from thermodynamic and kinetic points of view the separation of the &agr;-phase in the triple joints is more expedient than at the intergranular boundaries. As a result, a microduplex structure is formed.
[0161] When working billets of titanium and its alloys at the same extent of deformation, which is necessary for development of dynamic re-crystallization, the temperature-and-rate conditions of deformation per pass are selected so as to provide static re-crystallization in the &bgr;-phase during the subsequent heat treatment that allows one to include in the transformation process of structure in larger layer in the billet processed by torsion or by torsion with tension. The re-crystallization annealing between the passes provides a progress of the static and metadynamic re-crystallization in these layers that in combination with the preceding plastic deformation by the dynamic re-crystallization provides an increased uniformity and completeness of formation of intergranular boundaries in the &bgr;-phase. The following heat treatment is aimed at a phase transformation developed by the diffusion mechanism, like in the preceding case, enables one to obtain a structure of the microduplex type.
[0162] When working the billets of (&agr;+&bgr;) titanium alloys, at least in one pass the billet is deformed at a constant temperature not exceeding [TAc3=(20-30)]° C. When heated to this temperature, the microstructure, as a rule, represents colonies of lamellae of &agr;-phase in the matrix &bgr;-phase. In so doing the achieved minimum amount of the &agr;-phase does not change their laminated morphology, manifesting an ability of limiting the growth of the grains of the recrystallized matrix &bgr;-phase. The deformation heat treatment made in this case provides development of transformation of the rough laminated structure by one of the three schemes described above. These conditions are recommended for billets having an initial structure with a large enough size of the &bgr;-grain of about 1 mm and larger.
[0163] When working billets of a-titanium alloys, at least in one pass the billet is deformed at a constant temperature in a range of TAc3 and TAr3 for the processed alloy. The working of alloys of this group in the two-phase &agr;+&bgr; temperature range makes it possible to fully realize the advantages of the &bgr;-phase working under conditions of constrained growth of grains in the two-phase region.
[0164] The heat treatment in the billets subjected to deformation in passes or at steps is carried out by cooling with a regulated rate to provide a progressive direct phase transformation by the diffusion mechanism to providing &bgr;→&agr; transformation mainly in the triple joints and at the intergranular boundaries of the &bgr;-phase.
[0165] The cooling rate is taken not higher than the rate corresponding to the martensite transformation in the &bgr;-phase and not lower than the rate corresponding to the greatest intensity of formation of the annealing twins in the &agr;-phase. For many alloys this rate is optimal from the point of view of simultaneous progress of the following processes: phase transformations by the diffusion mechanism, re-crystallization, including metadynamic re-crystallization, as well as formation of annealing twins promoting the development of the process of fragmentation of the &agr;-lamellae during the subsequent heating.
[0166] The cooling is effected to a temperature of the next pass so as to combine the completion of the heat treatment process with the deformation process. In this case the decrease of time for cooling and heating makes a positive impact on the reduction of final grain size of the transformed microstructure.
[0167] The temperature of the next pass is taken below the temperature of the preceding pass. When it is required to obtain a minimum possible grain size, the process must be carried out with a decrease of temperature during each pass. The treatment of the billets per pass in this case may be considered as a method of increasing the plasticity resource of the billet during its working at the subsequent steps at a lower temperature due to gradual reduction of grains. The decrease of temperature and the increase of the plasticity reserve due to a fine grain of the transformed microstructure obtained during the treatment of the billets at the preceding steps enables one to increase the extent or rate of deformation in a combination with a temperature decrease, makes it possible not only to activate the development of the dynamic re-crystallization in the subsequent passes but also to obtain a transformed microstructure with a smaller grain size.
[0168] The temperature of the next pass is selected to be equal to the temperature of the preceding pass. When it is necessary to provide complete transformation, the uniformity of distribution of grains in the volume due to combination of the deformation working with thermal treatment, for example, in the case of working single-phase materials, it is expedient to carry out the working in the passes at the same temperature.
[0169] The cooling is effected to a temperature below the temperature of the next pass, with subsequent heating to the next pass temperature. Such a thermocyclic working is used to provide complete phase transformation a progress of direct phase transformations and to intensify the process of structure transformation.
[0170] The cooling to room temperature with subsequent heating to the temperature of the following pass, especially with a regulated rate, provides appearance phase cold hardening necessary for performing in the lamellae of the &agr;-phase recovery, or polygonization or twinning. The imposing of the processes phase cold hardening on the process of recovery accelerates the formation of low-angle boundaries and twinning. The subsequent heating results in fragmentation of &agr;-phase lamellae by structural defects, namely, by low-angle boundaries and twins during the reverse phase transformation.
[0171] At least after one pass the billet is heated to a temperature above the temperature of its working in the preceding pass and cooling to a temperature of the next pass. The expediency of such an operation is stipulated by a possibility in some cases, for example, when working materials subject to phase transformations at heating, to effect the process of transformation of the structure at the step of development of reverse phase transformations.
[0172] At least in one pass the working of the billet is carried out at a variable temperature. The urgency of the given operation becomes apparent on an example of working &agr;-titanium alloys, when the temperature range of simultaneous existence of the &agr;&bgr;-phases is extremely narrow, therefore, the treatment of the billets at a variable temperature, that is in an internal oscillation mode or with a short-term exit beyond the limits of the two-phase region, is one of techniques for obtaining a microcrystalline structure in these materials. Besides, the combination of the deformation with thermocycling makes active the processes of fragmentation of the &agr;-lamellae both due to formation of fragments during the deformation and due to development of direct and reverse phase transformations.
[0173] When working the billets of titanium and its alloys with an original cast structure, before performing the first step, preconditioning is carried out to provide dynamic re-crystallization in the &bgr;-phase and a heat treatment to provide a progressive reverse phase transformations. The rather soft method for working allows one to use the mechanical features of the working by torsion, to begin the working of a material having a cast structure, and to provide development of the dynamic re-crystallization in the &bgr;-phase. An additional effect consists in homogenization, i.e. leveling of the chemical composition in the ingots by volume in time by orders of magnitude shorter than at the traditional heat treatment.
[0174] When working the billets of titanium and its alloys with an original cast structure, the first step is preceded by preconditioning providing dynamic re-crystallization in the &bgr;-phase and a heat treatment providing progressive phase transformations. When working some billets, for example, prepared by homogenizing annealing but still having a cast microstructure, it is possible to perform their working by deformation in the two-phase region near the point Ac3. In so doing the dynamic re-crystallization in the &bgr;-phase layers located between the lamellae of the &agr;-phase will not be accompanied by fast growth of the &bgr;-grains, and the subsequent heating of the billet in the single &bgr;-phase region will allow one to use the recrystallized grain as nucleuses at reverse phase transformations improving the uniformity of distribution of the &bgr;-grains in the volume of the processed billet.
[0175] The deformation temperature at the next steps is selected below the deformation temperature at the first step. The expediency of the given restriction is determined by the fact that at the next steps of working of the billet it is possible to use intensive deformation aimed at shaping of the final product. It is well known that the intensive working is accompanied by an intensive release of heat that can result in coarsening the microstructure having been already transformed at the preceding steps.
[0176] The plastic deformation of the billets is carried out in one step, in which case a number of passes and an the accumulated deformation level are selected depending on the depth of the layer being treated and plasticity resource of the processed material. The necessity of this condition is stipulated by the plasticity resource, which is limited in each specific case and is determined by the initial microstructure of the processed material and conformity of ultimate deformation in the surface layers of the processed billet to the plasticity resource available
[0177] When the deformation is carried out in two steps, the value of the accumulated deformation at the first step is preferably selected from the condition of provision of reduction of the microstructure throughout the billet volume, which is determined from the relation: 2 V 1 ≥ V 0 σ 2 ( σ 1 + σ 2 )
[0178] where:
[0179] Vo is the volume of the whole billet;
[0180] V1 is the volume of the transformed part of the billet,
[0181] &sgr;1 is the flow stress of the material with a microcrystalline structure;
[0182] &sgr;2 is the flow stress of the material in the starting billet, the temperature of the second step being selected below the temperature of the first step of deformation;
[0183] This expression has been found theoretically when analyzing the situation, when a composite material is deformed. In so doing we assume that the mechanical behavior of individual elements of a composite and behavior of the composite as a whole is connected by a additivity principle.
[0184] If the deformation is carried out in three steps, at the third step the axial loading component is used for shaping the billet. When the manufacture of any component is connected with a significant change of its shape accompanied by intensive shear deformation, at the first steps it is expedient to prepare the microstructure in one sections of the billet, and in the other sections to combine the preparation of the structure with intensive deformation.
[0185] The starting billet is an axially symmetric billet in the form of a rod whose cross-sectional area is taken the smaller, the smaller the preset grain size; uniaxial tension being taken as an axial component. One of the parameters determining the process of preparation of the structure is the initial geometry of the processed billet. A reduction of the cross-sectional area of the billets provides a possibility of using the heat and cooling rate for solving the problem of obtaining a microstructure with a specified grain size and necessary uniformity of their distribution throughout the billet volume. Besides, when working large-size axially symmetric billets, their weight can be increased without changing their diameter but just changing only their length. In this case it is possible not only to extend the spectrum of obtained structures but also to increase the process efficiency. Since for one work cycle it is possible to process one long-length billet by torsion with tension followed by subsequent division into several billets instead of working individual short billets with observance of the ratio of the billet height to the diameter that is critical for the compression.
[0186] The starting billet is an axially symmetric billet in the form of a washer whose height is taken the smaller, the smaller the preset grain size, in so doing uniaxial compression is used at the second step, as an axial loading component. When working the billet in the form of a washer type, the necessity of reduction of the height dimension is stipulated by the tendency of varying the heating or cooling rate in a wide range to extend the range of achievable grain size of the transformed microstructure including the minimum possible one.
[0187] At the first step billet is deformed by a combination of torsion and compression. The torsion with compression allows one to deform the billet to a significant extent. This operation provides an additional decrease of the re-crystallization temperature and, as a consequence, to reduce the mean grain size in the transformed structure. The given operation is recommended for working such machine members as washers.
[0188] At first step the billet is deformed by a combination of torsion with tension. The basic loading component is torsion. However, to intensify the process of transformation, on the one hand, and to increase the stability of deformation of the rod, on the other hand, the torsion must be combined with axial loading. When working the long-length billets it is expedient to use tension for this purpose.
[0189] At the first step, the billet is deformed by combining alternating torsion with an alternating axial load. The broken path of deformation in the drawing (with a break angle on the line of deformation in the space “torsion—axial deformation” equal to 90°), realized at the first step of the structure preparation, is aimed at creation of conditions of development of concentrated multiple slip of dislocation of a different type taking place homogeneously in the whole volume of the processed billet. In so doing the processes of formation of a cellular polygon structure are facilitated depending on the temperature and rate of the deformation; the processes of re-crystallization and phase transformation are accelerated and, as a result, the processes of transformation of the laminated structure and formation of a microcrystalline structure of the microduplex type are intensified.
[0190] At the first step the monotonic torsion is combined with alternating axial loading. When working the axially symmetric billets having a length not exceeding the critical size by the criterion of stability at the compression, it is expedient to use torsion as a basic component of the loading and the uniaxial tension is combined with uniaxial compression. This technique, alongside with intensification of the process of transformation of the structure, allows one to decrease the value of the axial loading component approximately for 25-50%.
[0191] At the first step the billet is deformed combining alternating torsion with monotonic axial loading. The use of reverse torsion as a loading component, alongside with intensification of the process of transformation of the structure due to an increase of the amount of allowable accumulated deformation, promotes diffusion of the crystallographic and metallographic textures, and formation of a microcrystalline structure with a non-structural state.
[0192] At the first step, with monotonic two-component loading, the ratio between the axial component of the deforming force and the torsion component is not in excess of 0.2.
[0193] When working the billets, such a ratio of the torsion and tension components with monotonic two-component loading allows one to efficiently use the complex loading for intensification of the process of transformation of the coarse structure and for obtaining a microcrystalline structure in the surface layers of the billets.
[0194] At the second step the billet is deformed by a combination of compression and torsion. The use at the second step of compression as a primary loading component should be preferable in cases when the processed billets have a length not exceeding the triple minimum cross-sectional size. If otherwise, during the deformation by compression the billet stability will be lost. Besides, a combination of torsion with compression makes it possible to significantly reduce the forces required for overcoming the harmful effect of the frictional forces. This takes place due to the turn of the resultant vector of deformation and finally leads to a decrease of the axial force for 25-50% and to an increase of the working tool wear resistance.
[0195] At the second step the billet is deformed using a combination of torsion with tension. The use of the tension as a primary component at the second step of working of the billets is preferable when the processed billets have a length of the working part three times their minimum cross-sectional size.
[0196] When working the materials having a coarse structure and characterized by a limited plasticity resource, for example intermetallides, the plasticity resource of the billets can be increased by working them in a sheath. In so doing the fracturing on the lateral surface of the billet in many respects will depend on the gap between the sheath and the lateral surface of the processed billet. By deforming the sheath by uniaxial tension imparting to it superplastic property, it is possible to obtain a tight contact of the sheath with the surface of the processed billet and, as a result, the task of increasing the plasticity resource of the material will be achieved successfully. An increase of the sheath thickness, in a combination with a proper choice of the material will provide deformation of the billets under conditions close to the conditions of uniform compression and this also improves the plasticity resource of the processed material. In other cases the sheath can be used for prevention of oxidation of the billets during the deformation in atmospheric air.
[0197] The process of deformation of hollow billets using torsion as a primary loading component is limited to deformation, after which the hollow billet loses its stability. Therefore, in order to increase the extent of stable deformation, the hollow billets are preferably deformed with a core placed inside the billet. Besides, if torsion with tension are used at the step of working of the billet, the core will prevent development of deformation due to reduction of the cross-sectional area of the hollow billet, i.e. it will provide a possibility of creation in the hollow billet a scheme stress-strain state that is optimal from the point of view of the structure reduction, on the one hand, and preservation of the internal size of the hollow billet, on the other hand.
[0198] When working the hollow billet by multicomponent loading, the billet is provided with an internal core made of a material which, when working the billet, is deformed under superplasticity conditions, while at the second step the deformation is used for shaping both the core and the billet. The working of hollow billets with a core made of a material capable to be deformed under the superplasticity conditions, in addition to the above-mentioned advantages, allows one to rather easily take off the billet from the core due to the deformation of the core by tension with uniform reduction of its cross-sectional area along its length and formation of a guaranteed gap between the billet and the core.
[0199] The billet with the core is deformed in a sheath made of a material capable of performing superplastic properties during the deformation. In so doing the sheath is prepared by uniaxial tension to provide a contact between the billet and the sheath along the lateral surface of the billet preventing their displacement relative to each other in the process of working. The expediency of the deformation of the hollow billet in a sheath is already described in the preceding sections of the specification. The main task of this operation is to increase the plasticity resource during the deformation of thin-walled sheaths from brittle materials with a limited plasticity resource, as well as an increase of stability during the plastic deformation, both by torsion and tension or compression. In addition, we solve the problem of leveling the temperature field in the volume of the thin-walled billet during the deformation not due to a uniform temperature field in the furnace, but due to redistribution of the temperature by a heat transfer through the sheath and core.
[0200] The core is made hollow when hollow billets with a large diameter and a small thickness are to be worked. In this case, since the total weight of the assembly is low, the problem of heat treatment of heavy billets is excluded, as mentioned above.
[0201] The core is made solid when it is important to provide uniform distribution of the temperature field through the volume of the hollow thin-walled billet due to the massive core by utilizing its weight, as some type of an accumulator of energy for increasing thermal inertia of the system. It is recommended in the case of working the materials with rather a narrow temperature range of their existence simultaneously in two allotropic modifications, for example, &agr;-titanium alloys.
[0202] The billet and the core are deformed jointly when the plasticity resource necessary for development of dynamic re-crystallization is insufficient, for example, in such materials as intermetallides.
[0203] The billet and the core are deformed separately when it is important to assemble the block before the working and to disassemble it after the working. It is used n cases, when the next steps of working are used for imparting to the billet required geometric dimensions using the core as a caliber. The working of the billet is carried out while the hollow core is expanded by pressure-feeding of the working fluid into the core internal space.
[0204] This operation, in addition to the basic loading components, such as torsion, tension, compression, intensifies the process of transformation of the structure in the hollow billet as well as can be used for collimating to billet and also can be used for imparting a required shape to the billet.
[0205] Placed between the billet and the core is a material, which at least when working the billets, acquires viscous-fluid properties. This operation is recommended to prevent setting of the billet and core, to provide uniform deformation and to simplify the operation of removal of the core from the billet.
[0206] After the working of the billet, the billet is expanded by pressure-feeding of the working fluid into the space between the billet and core. The expansion of the hollow billet provides uniform development of deformation along the billet length by reducing the friction between the billet and the core when the core is not deformed in the process of working.
[0207] The hollow thin-walled billets are worked in a sheath, in which case the billet is preliminarily expanded so as to provide contact between the billet and the sheath along the lateral surface of the billet preventing their displacement relative to each other in the process of working. The preliminary expansion of the billet allows one to provide uniform of deformation of the billet under conditions close to the conditions of overall compression. The creation of a tight contact between the billet and the sheath also allows one to increase the uniformity of the temperature field in the process of working.
[0208] The sheath is made of a material capable of undergoing superplastic deformation in the selected temperature-and-rate conditions of working the billet. It allows one to increase the extent of uniform distribution of the compressive forces through the cross-sectional area of the processed billet, on the one hand, and to provide uniform development of the deformation of the hollow billet, on the other hand. Besides, the sheath plays the role of a protective screen preventing oxidation of the thin-walled hollow billet during its deformation at high temperature in the air atmosphere.
[0209] The hollow billet is placed between the sheath and the core made of a material not undergoing deformation in the process of working of the billet, to provide a uniform contact over all contacting surface of the billet and core preventing mutual displacement of the billet, sheaths and core at working, and the billet is deformed by displacing the sheath and core relative to each other. The use of this loading scheme during the deformation of the hollow billet is in fact a technological operation, at which the shear deformation is effected due to displacement of the internal and external layers in the processed billet relative to each other by rotating the sheath and core rigidly connected to billet in the opposite directions. It seems that in this case insignificant displacement result in significant shear deformation throughout the billet volume. A key feature of development of such deformation is its high uniformity through the billet volume under condition of tight contact between the billet, sheath and the core. In so doing the tighter the contact, the higher the amount of the accumulated deformation. When working the billets of medium and large dimensions, it is possible to achieve an amount of deformation close to that possible when working microspecimens on the Bridgeman anvil. In this example, like in the preceding ones, a predominant type of loading is torsion. First of all, it is connected with a feature inherent in this type of loading consisting that the deformation at torsion is not accompanied by any significant change of the billet shapes like, for example, at tension or compression.
[0210] The billet and contacting surfaces of the sheath and core have a conical shape. On making the conical sheath and core matched with the billet and combining torsion with compression of the conical billet, while using primarily the torsional loading, it is possible not only to increase the axial deformation component, compared to the preceding case, but also to work the billets under quasi-hydrostatic conditions, i.e. under conditions of overall compression. From the point of view of the stressed-state scheme for large-size billets, such a technique is similar to the known methods of deformation used for obtaining micro-, submicro- and nanocrystalline structures in small-size billets under laboratory conditions. In so doing the proposed technique is unique, because by a possibility of creation of maximum hydrostatic pressure it is close to the Bridgeman anvil method, and by the uniformity of the stressed and deformed state in the whole volume it is similar to the method of equal-channel pressing. Therefore, this technique is a method for obtaining uniform micro-, submicro- and nanocrystalline structures in large-size billets.
[0211] What is more, in contrast to the above-mentioned methods, the described technique is characterized by the absence or minimum slip on the surface of contact of the billet relative to the sheath and core. This benefit allows one to use said technique also as a method of realization of intensive high-temperature shear deformation of large-size billets made of such materials as, for example, intermetallides of the Ti—Al or Ni—Al system, etc.
[0212] The contact between the hollow billet, sheath and solid core is provided due to thermal tightness development. When the billet, sheath and core have a cylindrical or conical surface with a small obliquity, for example, less than 7°, it is expedient to provide a tight contact due to creation of thermal tightness. In so doing it is necessary to adhere to the following rule: the billet being installed in the deforming tool should not be subjected to tensile forces. For example, first of all, there is provided a contact between the billet and the sheath, then between the assembly of the sheath and the billet core.
[0213] The contact between the hollow billet having thickness t, the sheath and the solid core is provided by means of brazing, the initial thickness of a braze layer &Dgr; being selected from the condition &Dgr;≦0.005 t. Such a thickness of the layer is selected for the purpose of increasing the hardness compared to hardness of the braze material, stemming from the specific boundary conditions on the surface of contact of the billet with the sheath and/or with the core. Like in the first case, the object is to provide tight contact and to prevent the slip. An additional object of this operation is a simple removal of the billet from the assembly at the expense of heating the billet above the melting point of the braze material.
[0214] When processing the lamellae to obtain micro-, submcro- and the nanocrystalline structure therein, the lamellae are placed between the sheath and the core to provide a contact over the whole surface by means of preliminary deformation of the lamellae, and in the process of working the shear deformation is effected by rotating the sheath and the core relative to each other. In this way it is possible to work not only hollow or ring-shaped billets, but also flat plates which before the working are ring-shaped and placed between the sheath and the core.
[0215] The sheath and core have a conical shape, the preliminary deformation of the lamellae is carried out during the assembly. The tight contact is formed directly in the process of working the lamellae.
[0216] When working the billets in the shape of bars, the torsion is carried out by applying deforming force to the end face surface uniformly over the area with a radius r equal to 0.7<r<R, where R is the radius of the processed billet. The application of the deforming force to the billet reduces the non-uniform deformation in the cross-section of the rod that is especially important for preparation of a microcrystalline structure uniformly throughout the volume of the processed billet.
[0217] The deforming force is applied to the billet being worked via the permanent joint connecting the billet with the working tool. This type of connection in a single production line is simple and inexpensive.
[0218] If a rod must be processed, fusion welding, for example, by an electronic beam in a close-range mode allows one to reliably connect the processed billet to the deforming tool.
[0219] If the processed material, when melted, forms an eutectic compound and then brittle intermetallde, the joint is preferably made by solid welding connecting the billet with the tool either directly or through an intermediate layer. The specific feature of this type of joint consists in that it is capable to withstand high static loads up to a level exceeding the level of the basic material and, at the same time, can be destroyed by applying a low dynamic or cyclic force. The last effect can be successively used for separation of the billet from the tool after the working.
[0220] The permanent joint can be made by brazing, in which case the braze material is selected from a condition that its melting point is higher than the temperature of working the billet, and the thickness of the braze layer is selected from the relation (0.005-0.01)D′, where D′ is the cross-sectional area of the connection of the billet with the tool. Like in the preceding case, after the treatment of the billets, the heating of the billets and tooling to the melting point of the braze material allows one to rather simply solve the problem of separation of the billet from the tool. The thickness of the brazing joint is selected stemming from the optimal ratio of the layer thickness to the cross-sectional area of the contact area providing contact hardening, which allows one to increase the hardness of connection by 20-50% of the value of the flow stress of the braze material.
[0221] The deforming force on the processed billet is transferred through a separable, usually, spline connection with the tool. This type of connection is preferably used when manufacturing billets at a mass production line, when the tool cost is readily paid off. The Spline connection can be made in the form of a set of longitudinal and transverse splines, arranged at an angle of 90° relative to each other, said splines being capable of transmitting both torque and thrust forces in the process of working the billet. When working thin-walled hollow billets, the splines are preferably made on the contact surfaces of the sheath and core.
[0222] At the analysis of sources of information relating to methods for working of metals and alloys, we have no method characterized by the features identical to the features of the present invention. Therefore, the claimed invention meets the “novelty” condition.
[0223] At the analysis of the distinctive features we have found that the claimed invention is not obvious over the known prior. For the first time there is proposed a method for working of metals and alloys under conditions of simple and complex loading including deformation of the billets by torsion in one or several stages. The method allows one to regulate the accumulated deformation, which in combination with heat treatments aimed at development of dynamic and/or static re-crystallization and, when working the materials characterized by phase transformations, allows one to obtain a micro-, submcro- and nanocrystalline structure having a preset size and uniform or regulated by irregular distribution of grains in volume of the processed billet including large-size billets.
[0224] Features of the invention will become apparent from the drawings and following detailed discussion, which by way of example without limitation describe preferred embodiments of the invention.
[0225] The apparatus whose schematic view is shown in FIG. 1 and a general appearance in FIG. 2 consists of the power housing 1 including a lower power plate 2 and an upper power plate 3 fixed to each other by four columns 4. A kinematic loading system 5 is located in the lower part of the housing. A system 6 for recording the power and kinematic parameters of the process is located in the upper part of the housing.
[0226] A specimen 7 is installed in replaceable clamps 8, 9 connected to a stationary upper bar 10 and to a movable lower bar 11.
[0227] The apparatus has an electronic control system 12, which is used for performing mechanical tests of the specimens with a constant extent of deformation or with a constant deformation rate. The kinematic circuit of the apparatus allows one to carry out deformation by uniaxial tension and compression, as well as by monotonic or reverse torsion. When tubular specimens are to be worked, the apparatus can be provided with a facility for loading the specimens by the internal pressure of a working fluid (this facility is not shown in FIG. 1).
[0228] The system for recording the power and kinematic loading parameters in the process makes it possible to perform independent records of the power and kinematic loading parameters: the angle of torsion and rotation; axial displacement and axial force; pressure of the gaseous working fluid in a digital format directly in a personal computer or on graph paper tape.
[0229] A high-temperature furnace 13 with an electronic control system 14 allows one to carry out experiments at a high temperature (up to 1000° C.) with an accuracy of ±5° C. The furnace design permits performance of various kinds of a heat treatment including a thermocycling routine.
[0230] As mentioned above, the apparatus has replaceable clamps 8, 9 for deforming specimens 7 of various shapes and sizes: from 10.0 mm in diameter and with the working part length of 40.0 to 100.0 mm in diameter and a length of the working part of 200.0 mm.
[0231] The apparatus makes it possible to develop a maximum stress-strain force of up to 150.0 &kgr;N and a torque of up to 300.0 Nm.
[0232] The method is realized in the described apparatus as follows.
[0233] The billet 7 is installed in the clamps 8 of the clamping device providing rigid fixing of the billet. In so doing the clamps are connected to the billet using a separable joint, for example a spline joint or a permanent joint, for example a brazing or welding joint. The billet installed in the clamps is heated to a preset temperature in the furnace 13 at an average heating rate of about 50° C./minute. After the operating temperature has been attained, the specimen is held at this temperature for approximately 15 minutes. Then the specimen is deformed under conditions specified in the claims.
[0234] The circuits of the pass-by-pass and stepwise working and the corresponding loading paths for various composition, shape and size of the billets are given in the examples.
[0235] The term “pass” means an operation of deformation of the billet in one, two or several runs or continuous loading including that along the path of deformation with an orthogonal bend. The passes can be separated by heat treatment operations.
[0236] The step means a set of operations of loading and heat treatment or only loading aimed at obtaining a given microstructure in certain parts of the billet.
[0237] In the process of working, the loading parameters are recorded continuously on a graph tape and in a file in a computer. In the process of tests the computer monitor displays the information on the accumulated deformation which is necessary for controlling the process of working the billets.
[0238] After the test the billet is taken off from the clamps of the separable clamping device. When the billet and the clamps are connected through a brazing joint, after the test the billet and the separable clamps are heated to a temperature above the melting point of the braze material, and the billet is released. When the billet and clamps are connected by welding, for example by electronic beam welding, the billet and clamps are separated by means of turning or by an electrical-discharge process. When the billet and clamps are connected by means of a solid-phase joint, after the test the bending dynamic action may be used alongside with turning and electrical-discharge treatment.
[0239] The following EXAMPLES are illustrative and should not be construed as a limitation on the scope of the claims unless a limitation is specifically recited.
EXAMPLE 1[0240] Subjected to the working is a billet of a two-phase (&agr;+&bgr;) titanium alloy VT9 of the martensite class (Ti-based; 5.8-7.0 Al; 2.8-3.8 Mo; 0.8-2.0 Zr; 0.2-0.3 Si) with a diameter of 10.0 mm and a length of the working part of 60.0 mm, using a dedicated apparatus for complex loading (FIGS. 1, 2).
[0241] FIG. 3 illustrates the microstructure and FIG. 4 shows an appearance of the processed billet in an initial state. The billet has a coarse laminated microstructure with a grain size of the transformed &bgr;-phase of D=0.5-1.0 mm. A similar type of the microstructure is typical for hot-rolled billets subjected to additional heat treatment—annealing at a temperature of 1100° C. for 30 minutes and subsequent cooling in air.
[0242] The transformation temperature Ac3, (&agr;+&bgr;→&bgr;) is determined by the method of trial quenching and for this material is equal to T=1000° C.
[0243] It is necessary to obtain a fine-grained microcrystalline structure with a mean grain size d=3.0-7.0 microns uniformly distributed throughout the volume of the billet.
[0244] Taking this into account, a two-step working is selected. At the first step a microstructure in the surface layer is prepared and at the second step the structure is prepared to a preset grain size throughout the volume of the billet, including its central part. It so doing, it is taken into account that at the first step, a microstructure with a mean grain size d=4.0-10.0 microns should be generated to provide the deformation of the material at the next steps under superplasticity conditions in surface layer.
[0245] The value of the worked layer of the material of the billet at the first step V1 determined from the expression (1), where
[0246] Vo=3141.59 MM3 is the volume of whole billet;
[0247] &sgr;1=15.0 MPa is the flow stress of the material with a microcrystalline structure at its deformation in the optimal range of temperature-and-rate conditions of superplastic deformation;
[0248] &sgr;2=40.0 MPa is the flow stress of the material with a coarse structure at its deformation in the optimal range of temperature-and-rate conditions of superplastic deformation.
[0249] The values &sgr;1 and &sgr;2 are found by the results of preliminary experiments of from references.
[0250] By the found value of V1 it is possible to find a extent of equivalent deformation along the lateral surface. In this case this deformation has make up a value e1=1.1-1.3.
[0251] At the first step of working the billet two-component proportional loading is selected. The primary component is simple torsion the additional component is uniaxial tension. The ratio of torsion component and tension is taken equal to 3 √ 3 Υ e = 10.0 1.0 i . e . less than 0 .2 .
[0252] i.e. less than 0.2.
[0253] From the analysis of reference literature it has been found that the optimal range of deformation rates for this material is within 10−4-10−3 s−1.
[0254] Both at the first and at the second steps of deformation the extent of deformation and the loading temperature-and-rate conditions are selected so as to provide the transformation of the structure during the loading, i.e. due to development of dynamic re-crystallization. In this example, like in the subsequent examples, the rate of deformation of the billet by the tensile component is taken constant during the whole process of deformation and equal to {square root}3&ggr;=1.0×10−3 s−1, and the rate of deformation of the billet provided by the tensile component is also taken constant and equal to e=1.0×10−4 s−1.
[0255] The deformation temperature at the first and second steps is taken of the same value and equal to T=950° C.
[0256] At the second step of the structure reconditioning uniaxial tension is taken as a loading component. The deformation rate at the second step, like at the first step, is also held constant and equal to ei=1.0×10−4 s−1 and the deformation is completed upon achieving the value of deformation intensity equal to ei=0.8.
[0257] The above-described routine and the program of loading at both steps are shown in FIGS. 5a and b.
[0258] After the first working step the specimen is cooled in air to room temperature. Then the specimen is again heated to a temperature of 950° C. with an average heating rate of 50° C./min, held at this temperature for 15 minutes and then is deformed by a uniaxial tension using the wording conditions and program of the second step, FIGS. 5 a, b.
[0259] Having completed the second step, the specimen is cooled in air and removed from the clamps.
[0260] The appearance of the billet after the working at the first step is shown in FIG. 6. The results of the metallurgical surveys which have been carried out after the working of the billet on the first and second steps are shown in FIG. 7. The quantitative metallographic study have shown that the value of the shape factor of &agr;-lamellae K&agr; for the central part of the processed billet is equal to 3.1 and for the peripheral part 2.0. The thickness of the &agr;-lamellae in the central part is equal to 2.2 in the peripheral part 2.4 microns.
[0261] Thus, we may draw a conclusion that the microstructure in the processed billet is transformed uniformly throughout the volume and has a microcrystalline structure with a mean grain size of d=3.5-5.0 microns.
EXAMPLE 2[0262] Subjected to the working is a cylindrical billet with a diameter of 20.0 mm and a length of the working part of 40.0 mm made of two-phase (&agr;+&bgr;) titanium alloy VT9 of the martensite class (Ti-base; 5.8-7.0 Al; 2.8-3.8 Mo; 0.8-2.0 Zr; 0.2-0.35 Si).
[0263] FIG. 3 illustrates the initial microstructure of the billet. The billet has a coarse laminated microstructure with a grain size of the transformed &bgr;-phase, D=0.5-1.0 mm. The temperature of the polymorphic transformation (&agr;+&bgr;→&bgr;) (point Ac3) is determined by the method of trial quenching and for the used material is equal to T=1000° C.
[0264] In this example it is necessary to obtain a microcrystalline structure with a mean grain size d=3.0-5.0 microns uniformly distributed throughout the volume of the billet. At the same time, the processed billet should have a shape of a flat disk 10.0 mm thick.
[0265] Both at the first, and at the second steps of deformation, the extent of deformation and the loading temperature-and-rate conditions are selected stemming from the conditions of transformation of the structure in the process of loading, i.e. at the expense of dynamic re-crystallization.
[0266] To attain this task, a two-step working is selected. At the first step a microstructure in the surface layer is prepared by deforming the specimen using two-component proportional loading.
[0267] The primary component is torsion and the additional one is compression. The use of this loading scheme is aimed at preparation of a microstructure, first of all, in the surface layers including layers located directly under the hammer blocks.
[0268] At the second step the structure in the central part of the billet is prepared to a preset grain size in the process of deformation of the billet by compression. In so doing the compression is also used for shaping the final article.
[0269] The amount of accumulated deformation along the lateral surface of the billet “e” is selected at the first step proceeding from the calculations made in analogy with Example 1 equal to 0.9-1.1, and after the second step equal to ei=1.0-1.25 proceeding from the final shape and dimensions of the billet. At the first step the deformation rate of the torsion component taken constant during the entire process of deformation and equal to {square root}3&ggr;=1.0×10.0−3 s−1 while the deformation rate of the compression component is also taken constant and equal to e=1.0×10−4 s−1. The deformation temperature at the first and second steps is taken equal to temperature T=950° C.
[0270] The rate of deformation by compression at the second step, as well as at the first step is constant and equal to e=1.0×10−4 s−1, and the deformation is completed upon attaining the deformation intensity equal to ei=1.25.
[0271] The program and the corresponding loading conditions described in this example are shown in FIGS. 8 a, b.
[0272] After the first working step the specimen is cooled in air to room temperature. Then the specimen is repeatedly heated to a temperature of 950° C. at an average heating rate of 50° C./min, held at this temperature for 15 minutes and deformed by uniaxial tension under the conditions and program of the second step, FIGS. 8 a, b.
[0273] Having completed the second step, the specimen is removed from the furnace and cooled in air.
[0274] The results of the metallographic study conducted after the working of the billets are similar to the results of Example 1. The shape factor of the &agr;-lamellae K&agr; for the central part of the processed billet is equal to 2.9 and for the peripheral part 2.1. The thickness of the &agr;-lamellae in the central part is equal to 2.1 microns in the peripheral part 2.4 microns.
[0275] Thus, we may draw a conclusion that the microstructure in the processed billet has been transformed uniformly throughout the billet volume and has a microcrystalline structure with a mean grain size of d=3.5-4.0 microns.
EXAMPLE 3[0276] Subjected to the working is a cylindrical billet of two-phase (&agr;+&bgr;) titanium alloy of martensite class VT6 (Ti-base; 5.3-6.8 Al; 3.5-5.3 V).
[0277] A cylindrical billet with a diameter and a length of the working part equal to 20.0 mm and 100.0 mm respectively in the initial state has a coarse laminated microstructure. FIG. 9 illustrates the billet microstructure in the initial state. The mean grain size of the transformed &bgr;-phase is equal to D=10.0-15.0 mm.
[0278] It is necessary to obtain a fine-grained microcrystalline structure with a mean grain size of d=4.0-8.0 microns in the peripheral part of the billet. A laminated microstructure is permissible in the central part of the billet.
[0279] In this example, like in examples 1 and 2, the extent of deformation and the loading temperature-and-rate conditions are selected proceeding from the conditions of transformation of the structure in the process of loading.
[0280] To attain the set task, a two-step working is selected (FIG. 10 a). The specimen is deformed by a single-component loading (FIG. 10 b). The single loading component is torsion. The deformation temperature is taken equal to 930° C. The billet is deformed at a constant deformation rate corresponding to its value on the lateral surface or {square root}3&ggr;=10−3 s−1.
[0281] According to the expression (1), the extent ei of the accumulated deformation on the lateral surface is taken equal to 2.0. The preset extent of deformation is sufficient for working the microstructure in the billet for a half of its volume. The heating rate is taken equal to 50° C./min and after the working the billet is cooled in air.
[0282] FIG. 11 illustrates the macrostructure of the deformed specimen and FIG. 12 illustrates the microstructure of the same. The results of the conducted metallographic study have shown that the shape factor of the &agr;-lamellae K&agr; for the central part of the processed billet is equal to 7.6 and for the peripheral part to 2.5. The thickness of the &agr;-lamellae in the central part is equal to 2.9 microns and of the peripheral part to 3.3 microns.
[0283] Thus, we may draw a conclusion that the structure in the working part of the processed billet has been transformed non-uniformly through the cross-section. The morphology of the structure in the central part has a laminated structure and on the periphery is has a equiaxial microcrystalline structure with a mean grain size of d=4.0-6.0 microns.
EXAMPLE 4[0284] Subjected to the working is a billet of two-phase (&agr;+&bgr;) titanium alloy VT9 (Ti-base; 5.8-7.0 Al; 2.8-3.8 Mo; 0.8-2.0 Zr; 0.2-0.35 Si).
[0285] The appearance and geometric dimensions of the billet in the initial state were as in Example 1 (FIG. 4).
[0286] The billet has a coarse laminated microstructure with a grain size of the transformed &bgr;-phase equal to D=1.0-2.0 microns (FIG. 3). The temperature of the polymorphic transformation (&agr;+&bgr;→&bgr;) or the point Ac3 is determined by the method of trial hardening and for this material is equal to T=1000° C.
[0287] It is necessary to obtain a fine-grained microcrystalline structure with a mean grain size of d=3.0-7.0 microns uniformly distributed throughout the billet volume. Therefore, taking into account that in the initial state the billet has a coarse laminated structure and its plasticity reserve is limited to development of the dynamic re-crystallization processes in the &agr;-phase, a two-step working is selected with three passes at the first step. In all three passes of the first working step, and also at the second step, the extent of deformation and the loading temperature-and-rate conditions are selected so as to provide structure transformation in the process of loading at the expense of the dynamic re-crystallization in the &bgr;-phase.
[0288] The passes are separated by heat treatment operations aimed at development of phase transformations in the course of change of temperature and at the absence of a deforming effect on the billet.
[0289] The deformation temperature in all three passes of the first step, as well as at the second step, is taken equal to T=960° C. During the first pass of the first step the billet is deformed by torsion at a constant deformation rate of {square root}3&ggr;=1.0×10.0−3 s−1 to a value of deformation intensity ei1=0.5.
[0290] After the first pass the billet is heated for 15 minutes to a temperature on 1010° C. above the point Ac3. After the furnace has brought to a preset temperature, heating is switched off and the temperature is reduced to the preceding value by steps of 2.0° C./min.
[0291] The working of the billet in the second pass is carried out by proportional loading (torsion with simultaneous tension). The deformation rate of the torsion component is constant and equal to {square root}3&ggr;=1.0×10.0−3 s−1. The deformation rate of the tension component is also kept constant and equal to e=10−4 s−1. The ratio the components of the rates of deformation of torsion to tension is taken from the relation: 4 √ 3 Υ e = 10.0 1.0
[0292] The deformation is carried out to a value ei2=0.6. After the second pass the billet is cooled by 40-60° C. below the working temperature by steps of 2.0° C./min by reducing the heating rate of the furnace. Upon achieving a preset temperature, the heating rate of the furnace is increased up to the working temperature of the next pass.
[0293] The working of the billet in the final third pass of the first step is carried out using a uniaxial tensile force, deforming the billet at a deformation rate e=1.0×10−4 s−1 to a value of deformation intensity ei3=0.2.
[0294] The working scheme and the respective loading scheme in passes and at steps are shown in FIGS. 13 a, b.
[0295] The choice of the three-pass working scheme at the first step with an intermediate heat treatment aimed at development of the phase transformations has allowed us not only to increase the plasticity reserve and the accumulated deformation at the step due to reduction of the structure resulting from additional division of the lamella of the &agr;-phase during the reverse and direct phase transformations but also to increase the extent and uniformity of the transformation of the lamellae of the &agr;-phase in the surface layers of the billet.
[0296] After the first working step the specimen is cooled in air to room temperature, heated to the temperature of the second step and then deformed by uniaxial compression like in Example 1 under the second step operating conditions.
[0297] Having completed the working process, the billet is removed from the furnace and cooled in air.
[0298] It should be noted that the billet worked at the first step under the specified conditions, compared to Example 1, at the second step is deformed more uniformly with a less pronounced deformation relief on the lateral surface.
[0299] The results of the qualitative and quantitative metallographic studies of the processed billets have shown that the shape factor of the &agr;-lamellae K&agr; for the central part of the processed billet is equal to 3.0 and for the peripheral part 2.1 microns. The thickness of the &agr;-lamellae in the central part is equal to 2.4 and the peripheral part 2.4 microns.
[0300] Thus, we may draw a conclusion that the microstructure in the processed billet has been transformed uniformly throughout the billet volume and has a microcrystalline structure with a mean grain size of d=3.0-4.0 microns.
EXAMPLE 5[0301] Subjected to the working is a cylindrical billet of a two-phase (&agr;+&bgr;) titanium alloy VT5-1 (Ti-base; 5.8-0.0 Al; 2.8-3.8 Mo; 0.8-2.0 Zr; 02-0.35 Si) having a diameter of 40.0 mm and a length of the working part of 80.0 mm.
[0302] The billet has a coarse laminated microstructure with a grain size of the transformed &bgr;-phase equal to D=1.2-2.0 mm (FIG. 3). The temperature of the polymorphic (&agr;+&bgr;→&bgr;) transformations, point Ac3, is determined by the method of trial hardening. For this material the point Ac3 is equal to T=1000° C.
[0303] It is necessary to obtain a uniform microcrystalline structure in the billet volume with a mean grain size of 2.0-4.0 microns. Taking into account that in the initial condition the billet has a coarse laminated structure and the plasticity reserve is insufficient for using the temperature-and-rate working conditions for development of dynamic re-crystallization in the &agr;- and &bgr;-phases, the two-step working is chosen. The first step is effected in two passes. The passes are separated by heat treatment operations for static re-crystallization amplifying the insignificant dynamic re-crystallization occurring in the process of deformation aimed at formation of boundaries of grains in the &bgr;-phase and this, in a combination with the additional heat treatment, provide direct phase transformations in the process of a varying temperature and the absence of a deforming effect on the billet, thereby accelerating the separation of the laminae of the &bgr;-phase and forming a microcrystalline structure.
[0304] The loading of the billet at the first step is effected by a combination of alternating torsion with alternating axial force, i.e. at the first step the billet is deformed by clockwise torsion with subsequent compression, and at the second step the billet is deformed by counterclockwise torsion with tension. The deformation path at such loading is a closed circuit. The choice of such a loading scheme in the process of working is aimed at intensification of transformation of the laminated structure and at formation of a microcrystalline structure close to the non-structural state. At the second step billet is deformed by tension.
[0305] The temperature of deformation at the first and second step is chosen the same equal to T=960° C.
[0306] In the first pass of the first step the billet is deformed by clockwise torsion with constant speed of deformation equal to {square root}3&ggr;=1.0×10−3 s−1 up to a value of deformation intensity ei1=0.9. The torsion is followed by compression. The deformation rate is maintained constant and equal to e=1.0×10−4s-1. The deformation is effected to value ei2=0.2.
[0307] After the first pass has been completed, the billet is held at the working temperature for 15 minutes. Then the billet is cooled to a temperature of 900° C. stepwise at a cooling rate of 1.5° C./min. After cooling the billet to a preset temperature, it is heated again to the working temperature in the second pass.
[0308] In second pass of the first step the billet is deformed by counter-clockwise torsion at a constant deformation rate equal to {square root}3&ggr;=1.0×10−3 s−1 to a value of deformation intensity ei3=0.9. The torsion is followed by tension. The deformation rate is held constant and equal to e=1.0×10−4 s−1. The deformation is carried out to value ei4=0.2.
[0309] After the second pass the billet is held at a working temperature for 15 minutes then it is cooled to room temperature in air.
[0310] The billet at the second step is deformed by tension at a deformation rate corresponding to appearance in the worked material of superplasticity e=1.0×10−4 s−1 to a value of the deformation intensity equal to ei3=1.0. Having completed the process of working, the billet is removed from the furnace and cooled in air.
[0311] The scheme of working and loading of the billet in passes and at steps is shown in FIGS. 14 a, b. The choice of the loading scheme at the first step with an intermediate cooling aimed at development of phase transformations making it possible not only to increase the plasticity reserve and to increase the accumulated deformation at the step due to reduction of the structure as a result of additional separation of the lamellae of the &agr;-phase during the reverse and direct phase transformations, but also to increase the extent and uniformity of transformation of the lamellae of the &agr;-phase in the surface layers of the billet.
[0312] The results of qualitative and quantitative metallographic studies of the processed billets have shown that the values of the shape factor of the &agr;-lamellae and K&agr;-lamellae for the central part of the processed billet is equal to 2.8 microns and for the peripheral part to 2.5 microns. The thickness of the &agr;-lamellae in the central part is equal to 2.4 microns and in the peripheral part 2.5 microns.
[0313] Thus, we may draw a conclusion that the microstructure in the processed billet has been transformed uniformly throughout its volume and has a microcrystalline structure with a mean grain size of d=3.0-4.0.
EXAMPLE 6[0314] A billet of &agr;-titanium alloy VT5-1 (Ti-base; 4.3-6.0 Al; 2.8-3.8 Zr; 0.2-0.35 Si) having a diameter of 40.0 mm and a length of the working part of 80.0 mm is subjected to working.
[0315] The billet has a coarse laminated microstructure with a transformed &bgr;-phase grain size equal to D=1.2-2.0 mm (FIG. 3). The temperature of the reverse polymorphic transformation (&agr;+&bgr;→&bgr;), point Ac3, and direct polymorphic transformation (&agr;+&bgr;→&agr;), point Ar3, is determined by the method of trial hardening. For this material the point Ac3 is equal to T=1000° C.
[0316] It is necessary to obtain a uniform microcrystalline structure in the billet volume with a mean grain size of 2.0-4.0 microns.
[0317] In this example the billet is worked in one step consisting of three passes. Taking into account a narrow range of the two-phase region, as well as the initial coarse microstructure, the billet in the first pass is worked at a temperature of 950° C., in the second pass at a temperature of 1050° C., in the third pass at a temperature of 980° C.
[0318] The passes are separated by heat treatment operations aimed at development of reverse and direct phase transformations. The additional heat treatment in a combination with hot deformation under conditions of complex loading aimed at acceleration of the process of reduction of the structure.
[0319] In each of the three passes the billet is deformed by proportional two-component loading (reverse torsion with simultaneous tension).
[0320] In the first pass clockwise torsion is used as a primary component and uniaxial tension is used as a secondary component. The ratio the component of rate of deformation by torsion to that by tension is taken equal to: 5 √ 3 Υ e = 10.0 1.0
[0321] The deformation rate of the torsion component is taken constant and equal to {square root}3&ggr;=1.0×10−3 s−1, and the deformation rate of the tension component is also taken constant and equal to e=2.0×10−4 s−1. The deformation intensity at this step is taken equal to ei=1.2.
[0322] After the first pass the billet is heated at a rate of 5° C./min to the temperature of the second pass and the billet is deformed under the conditions of the second pass.
[0323] In the second pass counterclockwise torsion is used as a primary component and uniaxial tension is used as a secondary component. The ratio the component of rate of deformation by torsion to that by tension is taken equal to: 6 √ 3 Υ e = 10.0 1.0
[0324] The deformation rate of the torsion component is taken constant and equal to {square root}3&ggr;=1.0×10−3 s−1, and the deformation rate of the tension component is also taken constant and equal to e=2.0×10−4 s−1. The deformation intensity at this step is taken equal to ei=1.2.
[0325] After the second pass the billet is heated at a rate of 1° C./min to the temperature of the third pass, and the billet is deformed under the conditions of the third pass.
[0326] In the third pass clockwise torsion is used as a primary component and uniaxial tension is used as a secondary component. The ratio of torsion component to the tension component is taken equal to: 7 √ 3 Υ e = 10.0 1.0
[0327] The deformation rate of the torsion component is taken constant and equal to {square root}3&ggr;=1.0×10−3 s−1, and the deformation rate of the tension component is also taken constant and equal to e=2.0×10−4 s−1. The deformation intensity at this step is taken equal to ei=1.2.
[0328] The working of the billet is effected under conditions presented in FIGS. 16 a, b. After the working the billet is cooled in air.
[0329] The results of the qualitative and quantitative metallographic studies of the processed billets have shown that the average grain size in the center and at the periphery is d=5.0-7.0 microns.
EXAMPLE 7[0330] Subjected to the working is a billet of a two-phase (&agr;+&bgr;) alloy VT9 (Ti-base; 5.8-7.0 Al; 2.8-3.8 Mo; 0.8-2.0 Zr; 0.2-0.35 Si) having a diameter of 40.0 mm and a length of the working part of 80.0 mm. The billet has a coarse laminated microstructure with a grain size of the transformed &bgr;-phase equal to D=1.0-2.0 mm (FIG. 3). The temperature of the polymorphic transformation (&agr;+&bgr;+&bgr;), point Ac3, is determined by the method of trial hardening. For this material the point Ac3 is equal to T=1000° C.
[0331] Since the billet in the initial state has a coarse laminated structure with a limited plasticity reserve and it is necessary to obtain a sufficiently small size of the grain in order of d=1.0-2.0 microns, a two-step working is selected with a decrease of temperature during the passes. The first step is effected in three passes. The extent of deformation and the temperature-and-rate conditions of the working per pass are selected so as to provide dynamic re-crystallization. The passes are separated by heat treatments aimed at development of direct phase transformations amplifying the process of reduction of the microstructure due to formation of &agr;-grains along the boundaries of the re-crystallized &bgr;-phase.
[0332] The working temperature of the first pass is taken equal to 960° C., the second—930° C., the third—900° C. In each of the three passes the billet is deformed by proportional two-component loading (torsion with simultaneous reverse axial action or torsion with tension). The use of this scheme makes it possible to provide adequate working of the billet at the first step.
[0333] In the first pass the billet is deformed by torsion with simultaneous tension. The torsion is a primary component and the uniaxial tension is a secondary component. The ratio of the torsion component to the tension component is taken equal to 8 √ 3 Υ e = 10.0 1.0
[0334] The deformation rate of the torsion component is taken constant and equal to {square root}3&ggr;=1.0×10−3 s−1. The deformation rate of the tension component is also taken constant and equal to e=2.0×10−4 s−1. The deformation intensity per pass is taken equal to ei=0.6. After the first pass the billet is cooled to a temperature of the next pass at a rate of 1° C./min and deformed in the second pass mode.
[0335] In the second pass the billet is deformed by torsion with simultaneous tension. The torsion is a primary component and the uniaxial tension is a secondary component. The ratio of the torsion component to the tension component is taken equal to 9 √ 3 Υ e = 10.0 40.0
[0336] The deformation rate of the torsion component is taken constant and equal to {square root}3&ggr;=1.0×10−3 s−1. The deformation rate of the tension component is also taken constant and equal to e=4.0×10−4 s−1. The deformation intensity at the step is selected equal to ei=1.2. After the second pass has been completed, the billet is cooled to a temperature of the next pass at a rate of 1° C./min and deformed under the third pass conditions.
[0337] After the first step the billet is cooled in air to room temperature.
[0338] At the second step the billet is heated to a temperature of 900° C. in the furnace, held at this temperature for 15-20 minutes and deformed by uniaxial tension at a rate of 5.5×103 s−1 to an extent of deformation equal to ei=1.0.
[0339] The schematic diagrams of the working and loading are shown in FIGS. 16 a, b.
[0340] After the working the billet is removed from the furnace and cooled to room temperature in air.
[0341] The results of the qualitative and quantitative metallographic studies of the processed billets have shown that the average grain size in the center and at the periphery is d=5.0-7.0 microns.
EXAMPLE 8[0342] Subjected to the working is a billet of titanium alloy VT8 (Ti-base; 5.8-7.0 Al; 2.8-3.8 Mo; 0.2-0.35 Si) having a diameter of 30.0 mm and a length of the working part of 100.0 mm. The appearance of this billet is not shown in the figure.
[0343] FIG. 17 illustrates a microstructure of the material in the initial state. The grain size of the transformed &bgr;-phase is D=1.0-2.0 mm. The temperature of the Ac3 (&agr;+&bgr;→&bgr;), is determined by the method of trial hardening and for this material is equal to T=1010° C.
[0344] It is necessary to obtain a uniform fine-grain microcrystalline structure with a mean grain size of 5.0-7.0 microns uniformly distributed throughout the billet volume.
[0345] Taking this fact into account, a two-step working is chosen (FIGS. 18 a, b) with two passes at the first step. At the first step a microstructure in the surface layer is prepared, and at the second step the structure is preconditioned to obtain a preset grain size including the central part of the billet.
[0346] The amount of the processed layer at the first step and the corresponding extent of the accumulated deformation are determined like in Example 1.
[0347] The first step is effected in two passes. The deformation in the first and second passes is effected at a variable temperature. The temperature at the beginning of the working in the first pass is T=900° C. In the process of deformation the temperature is gradually increased to 960° C., then, in the second pass it is again decreased to the initial level. The working at the second step is performed by uniaxial tension at an optimal deformation rate corresponding to the superplasticity of the billet material.
[0348] The loading scheme, extent and rate of deformation in the first and second passes are the same: two-component proportional loading (FIGS. 18 a, b). The primary component is simple torsion, the secondary component is uniaxial tension. The ratio of the torsion component to the tension one is taken equal to 10 √ 3 Υ e = 10.0 2.0 i . e . less than 0 .2 .
[0349] The deformation rate of the torsion component is taken constant and equal to {square root}3&ggr;=4.0×10−3 s−1. The deformation rate of the tension component is also taken constant and equal to e=8.0×10−3 s−1. The deformation intensity per step is taken equal to ei1=ei2=0.8. After the first pass the billet is cooled to room temperature. At the second working step the billet is heated to a temperature of 900° C. in a furnace, held at this temperature for 10-15 minutes and deformed by uniaxial tension at a rate of 5.5×10−3 s−1 to an extent of ei=0.8.
[0350] The results of the qualitative and quantitative metallographic studies conducted are given in FIG. 19. The quantitative metallographic studies of the billets conducted after the final treatment at the second step have shown that the shape factor of the &agr;-laminae K&agr; for the central part is equal to 2.0 and for the peripheral part 2.1. The thickness of the &agr;-laminae in the central part is equal to 2.3 and in the peripheral part 2.4 microns.
EXAMPLE 9[0351] A large-size cylindrical billet of titanium alloy VT6 (Ti-base; 5.3-6.8 Al; 3.5-5.3 V) is subjected to working.
[0352] The billet has the following dimensions: a diameter of 140.0 mm and a length of 300.0 mm.
[0353] In the initial state the billet has a cast microstructure with a mean grain size of the transformed &bgr;-phase equal to 10.0-15.0 mm.
[0354] The temperature Ac3, (&agr;+&bgr;→&bgr;) of transformation for alloy VT6 is determined by the method of trial hardening and for this material is equal to T=990° C.
[0355] It is necessary to obtain a microcrystalline structure uniformly distributed throughout the billet volume and having a mean grain size of d=6.0-9.0 microns.
[0356] Since the material (alloy VT6) is delivered as a washer cut off from an ingot with diameter of 500.0 mm and a length of 200.0 mm, which had the shape and dimensions unacceptable for working in the available equipment, the washer is preliminarily cut into four parts. One part is subjected to a high-temperature deformation by compression with a change of the loading axes and subsequent drawing on a hydraulic press with a maximum capacity of 1600 ton force, on flat hammer blocks of the UISHB-510 isothermal stamp block. The temperature of start of the workings is taken equal to Ts=1100° C. and temperature of the end of the working is Te=930° C. After the working the forging is cooled in air. The forging had the following dimensions: diameter Ø 180.0 mm; length—320.0 mm. Then the forging is subjected to turning to the billet size.
[0357] The macrostructure of the billet cross section before the basic working is shown in FIG. 20. The billet had a coarse laminated microstructure with a grain size of the transformed &bgr;-phase equal to D=1.5-2.5 mm (FIG. 21) uniformly distributed throughout the billet cross section.
[0358] Prior to the working the billet is welded to the deforming tool made of heat-resistant titanium alloy by diffusion welding. The diffusion welding is effected using local sealing and evacuation in the joint zone. The conditions of the diffusion welding were as follows: temperature T=950° C.; welding force P=2.0 MPa; welding time &tgr;=15 minutes; negative pressure level B=1.010−3 Pa.
[0359] The working consisted of two steps (FIGS. 22, a, b) The working temperature at the first step is taken equal to T=950° C., and at second one T=930° C.
[0360] At the first step the billet is deformed by proportional two-component loading. The primary component is torsion and the secondary component is tension.
[0361] The ratio of the torsion component to the tension component is taken equal to 11 √ 3 γ e = 10.0 0.5
[0362] The deformation rate of the torsion component is taken constant and equal to {square root}3&ggr;=1.0×10−3 s−1. The deformation rate of the tension component is also taken constant and equal to e=5.0×10−5 s−1. The deformation is effected up to a value of intensity at the first step equal to ei=4.0.
[0363] After the first step the billet is cooled to room temperature. At the second step the billet is heated to a temperature of 930° C., held for 30 minutes and deformed by tension to an extent of deformation equal to ei=0.4. After the working the billet is cooled in a furnace to room temperature. Then the billet is separated from the tool using an electric process.
[0364] The appearance of the billet with welded separable clamps (tool) after the working at the final pass is shown in FIG. 23. A half of the processed billet cut along its axis is also shown in this figure.
[0365] FIG. 24 illustrates the billet macrostructure after the working. At the face end of the billet at a distance of approximately 30 mm there is seen the non-processed part of the structure, because the billet is selected of a larger size by length for carrying out the comparative analysis and subsequent metallographic studies.
[0366] The microstructure in the billet after the working is shown in FIG. 25. The quantitative metallographic study of the billets which has been performed after completing the second step of the final working step has shown that shape factor of the &agr;-lamellae K&agr; for the central part is equal to 2.0 and for the peripheral part 2.1. The thickness of the &agr;-lamellae in the central part is equal to 5.0 microns and in the peripheral part 4.9 microns.
[0367] Thus, we may draw a conclusion that the microstructure in the processed billet is transformed uniformly throughout its volume and has a microcrystalline structure with a mean grain size of d=8.0-9.0 microns.
EXAMPLE 10[0368] Subjected to the working is a cylindrical billet of two-phase (&agr;+&bgr;) titanium alloy VT9 of the martensite class (Ti-base; 5.8-7.0 Al; 2.8-3.8 0; 0.8-2.0 Zr; 0.2-0.35 Si) having a diameter of 50.0 mm and a length of the working part of 200.0 mm.
[0369] The material and the initial microstructure are similar those in Example 1. The microstructure has coarse laminated morphology with a grain size of the transformed &bgr;-phase equal of D=1.0-2.0 microns (FIG. 3).
[0370] The temperature Ac3 of the (&agr;+&bgr;→&bgr;) transformation is equal to T=1000° C.
[0371] It is necessary to obtain a microcrystalline structure with a mean grain size of d=2.0-3.0 microns uniformly distributed throughout the billet volume.
[0372] The billet (FIG. 26) is worked at two steps in a sheath having a thickness of 4.0 mm, with internal diameter of 52.0 mm and a length of 200.0 mm made of titanium alloy VT14 with a microcrystalline structure and a mean grain size of d=1.0-2.0 microns. The first step is effected at a reduced temperature T=880° C. and the second step at a temperature of 920° C.
[0373] It is taken into account that the working of the billet in a sheath not only increases the uniformity of the deformation along the length of the billet at its torsion with a slight tension but also the plasticity resource due to exception of formation riffles on the surface of the billet being worked similar to those observed when working the cylindrical billets after the first step in Example 1 (FIG. 6) and in Example 9 (FIG. 23). The exclusion of the formation of deformation relief suppresses the process of crack development.
[0374] A two-step working is selected as in similar Example 1 (FIGS. 5 a, b). At the first step a microstructure in the surface layer is prepared and at the second step the structure is prepared to a preset grain size throughout the billet volume including its central part.
[0375] The billet is put into the sheath in the space between sheath and billet create vacuum, the assembly is heated up to a temperature of 860° C., then the sheath is deformed by uniaxial tension before formation of a tight contact with the billet. The rate of deformation of the sheath is taken equal to 1.0×10−4c−1. Having completed the deformation, the temperature is brought to the working temperature of the billet at the first step. The billet and sheath are deformed jointly using two-component loading: torsion with simultaneous tension. The loading scheme, extent of deformation, as well as the rate of working the billet at the first step are selected as in Example 1.
[0376] Having completed the working at the first step, the billet in the sheath heated to a temperature of the second step and deformed using uniaxial tension. The loading scheme, the extent of deformation, as well as the rate of working the billet at the second step are selected as in similar Example 1.
[0377] After the working, the billet is removed from the furnace and cooled to room temperature in air. Then the sheath is removed by turning.
[0378] The metallographic analysis has shown that after the working the billet has a uniform microcrystalline structure throughout its volume with a mean grain size equal to d=1.5-3.0 microns.
EXAMPLE 11[0379] Subjected to the working is A tubular billet of two-phase (&agr;+&bgr;) titanium alloy VT9 of the martensite class (Ti-base; 5.8-7.0 Al; 2.8-3.8 Mo; 0.8-2.0 Zr; 0.2-0.35 Si) is subjected to working.
[0380] The billet has the following dimensions: an external diameter of 50.0 mm, an internal diameter of 40.0 mm; a length of the working part of 200.0 mm.
[0381] In this example use is made of a material with an initial microstructure similar to the microstructure of Example 1 (FIG. 3) having coarse laminated morphology with a grain size of the transformed &bgr;-phase equal to D=1.0-2.0 microns. The temperature Ac3 (&agr;+&bgr;→&bgr;) of transformation is equal to T=1000° C.
[0382] It is necessary to obtain a microcrystalline structure with a mean grain size d=2.0-3.0 microns, uniform throughout the billet volume.
[0383] Taking this into account, a two-step process is selected similar to that of Example 1 (FIGS. 6 a, b). At the first step a microstructure is prepared in a billet volume in the external layer, and at the second step the structure is processed to a preset grain size including the internal layers of the tubular billet.
[0384] At the first step the billet, like in Example 1, is deformed by a proportional two-component loading. The torsion is a primary component and the tension is a secondary component. The ratio of the torsion component to the tension component is selected as in Example 1.
[0385] In order to exclude the loss of stability of the tubular billet during its deformation at the first step and to increase the efficiency of transformation of the structure at the second step at the expense of complication of the deformation scheme while preserving rather a simple loading scheme, before the working, a solid core in placed inside the billet. The core is made of heat-resistant nickel VT14 and has an internal diameter of 38.0 mm and a length of 200.0 mm (FIG. 27). A layer of glass lubricant is applied on the external surface of the core. After that, the billet and core are heated to the first step temperature and deformed using the scheme and loading conditions of the first step. It should be noted that during the working only the billet is deformed.
[0386] After the working at the first step, the billet is cooled in air to room temperature. Then the billet is heated again to the second step temperature and is deformed by uniaxial tension. Having completed the deformation at the second step, the billet is expanded by pressure-feeding of the working fluid into the internal space, the fluid pressure varying within 2.0 to 3.0 MPa.
[0387] This movement can be combined with tension. In so doing the efficiency of transformation of the structure due to development of the grain-limited slip.
[0388] Then the billet with the core is cooled to room temperature and disassembled by removing the core.
[0389] The metallographic analysis has shown that the processed billet has a microcrystalline structure uniform throughout the billet volume with a mean grain size of d=2.0-3.0 microns.
EXAMPLE 12[0390] Subjected to the working is a tubular billet of two-phase (&agr;+&bgr;) titanium alloy VT9 of the martensite class (Ti-base; 5.8-7.0 Al; 2.8-3.8 Mo; 0.8-2.0 Zr; 0.2-0.35 Si).
[0391] The billet has the following dimensions: an external diameter of 50.0 mm, an internal diameter of 40.0 mm; a length of the working part of 200.0 mm.
[0392] In this case, like in preceding one, use is made of a material with an initial microstructure similar to the microstructure of Example 1 (FIG. 3) having coarse laminated morphology with a grain size of the transformed &bgr;-phase equal to D=1.0-2.0 microns. The temperature Ac3 (&agr;+&bgr;→&bgr;) of transformation is equal to T=1000° C.
[0393] It is necessary to obtain a microcrystalline structure with a mean grain size of d=2.0-3.0 microns, uniform throughout the billet volume.
[0394] Taking this into account, a two-step process is selected similar to that of Example 1 (FIGS. 6 a, b). At the first step a microstructure is prepared. At the second step the structure is processed to a preset grain size.
[0395] At the first step the billet, like in Example 1, is deformed by a proportional two-component loading. The torsion is a primary component and the tension is a secondary component. The ratio of the torsion component to the tension component is selected as in Example 1.
[0396] The tubular billet is worked in two steps jointly with a hollow core made of titanium alloy VT14 having a microstructure with a mean grain size of d=1.0-2.0 microns. The first step is performed at a reduced temperature T=880° C., the second step at a temperature of 930° C.
[0397] The use of a hollow core is necessary to exclude the loss of stability of the tubular billet during its deformation, particularly, at the first step and to increase the efficiency of transformation of the structure at the expense of complication of the deformation scheme while preserving rather a simple loading scheme. Therefore, before the working, a hollow core in placed inside the billet. The core is made of titanium alloy VT14 and has an internal diameter of 38.0 mm and a length of 200.0 mm (FIG. 28).
[0398] When the process of working is not associated with a significant change in the shape of the billet and core, it is advisable to apply a layer of a separating material, for example, glass lubricant on the external surface of the core to facilitate the process of separation of the billet and core after the working.
[0399] Then the billet and core are heated to the first step temperature and deformed using the scheme and loading conditions of the first step.
[0400] Prior to the working, the core is expanded inside the billet providing a uniform contact over the entire surface of billet and core by supplying gaseous argon under pressure. The pressure is varied in a range of P=2.3-3.0 MPa.
[0401] It should be noted that during the working both the billet and the core are deformed.
[0402] After the first step the billet is cooled in air to room temperature. Then the billet is heated again to the second step temperature and is deformed by uniaxial tension.
[0403] The controlled supply of gaseous argon during the movement of the billet with the core allows one not only to increase the efficiency of the process of transformation of the structure, but also to change the final shape of the billet.
[0404] Then the billet with the core are cooled to room temperature and disassemble. The core is removed by turning.
[0405] The metallographic analysis has shown that after this working, the billet has a uniform microcrystalline structure throughout the billet volume with a mean grain size of d=2.0-3.0 microns.
EXAMPLE 13[0406] Subjected to the working is a thin-walled billet having an external diameter of 50.0 mm, an internal diameter of 46.0 mm and a length of the working part of 200.0 mm made of titanium gamma aluminide (TiAl). In the initial state the billet has a coarse microstructure with a mean grain size of d=0.3-0.5 mm.
[0407] It is necessary to obtain in the billet a microcrystalline structure with a mean grain size of d=5.0-10.0 microns uniformly distributed throughout the billet volume.
[0408] The analysis of the reference data has allowed us to make a conclusion that the conditions of the working of titanium alloy VT9 can as a first approximation be used for working the titanium gamma aluminide.
[0409] Taking this fact into account, a two-step working is selected as in Example 1 (FIGS. 6 a, b). At the first step, preliminary preparation of the microstructure is effected. At the second step the preparation of the structure to a preset grain size is carried out.
[0410] Since the plasticity resource of the processed material is insufficient for effecting the whole cycle of loading, the working of the billet is effected between the sheath and the core having a necessary plasticity resource (FIG. 29).
[0411] Before the working, a hollow rod is placed inside the billet. The core has the following dimensions: an external diameter of 44.0 mm; an internal diameter of 34.0 mm; a length of the core of 250.0 mm. The billet and core are placed in a sheath. The sheath has the following dimensions: an external diameter of 62.0 mm; an internal diameter of 52.0 mm; a length of 250.0 mm. Both the sheath and the core are made of titanium alloy VT9 having a microcrystalline structure with a mean grain size of d=5.0-10.0 microns. Then the assembly is heated to a temperature of 900° C., and the sheath is deformed by uniaxial tension at a rate of 5.0×10−4 s−1. At the same time, gaseous argon is supplied into the core at a pressure of 2.0-3.0 MPa.
[0412] After the temperature has reached the working level, the billet is worked using the program, loading scheme and temperature-and-rate conditions of Example 1.
[0413] It should be noted that during the working the entire assembly is deformed simultaneously. After the working, the assembly is removed from the furnace and cooled in air to room temperature. The sheath and core are removed by turning.
[0414] The metallographic analysis has shown that after the working the billet has a uniform microstructure throughout its volume with a mean grain size equal to d=5.0-10.0 microns.
EXAMPLE 14[0415] Subjected to the working is a thin-walled tubular billet of two-phase (&agr;+&bgr;) titanium alloy VT9 of the martensite class (Ti-base; 5.8.-7.0 Al; 2.8-3.8 Mo; 0.8-2.0 Zr; 0.2-0.35 Si).
[0416] The billet has the following dimensions: an external diameter of 50.0 mm, an internal diameter of 46.0 mm, a length of the working part of 200.0 mm. The billet is made of a sheet by preliminary bending into a pipe with subsequent argon-arc welding along the generating line.
[0417] To obtain in the billet an initial uniform microstructure similar to the structure of Example 1, the billet is preliminarily annealed in a vacuum furnace at a temperature of 1100° C. for 2 hours. After the heat treatment the structure has coarse laminated morphology with a grain size of the transformed &bgr;-phase equal to D=0.5-1.0 mm.
[0418] It is necessary to obtain a microcrystalline structure with a mean grain size of d=2.0-3.0 microns, uniform throughout the billet volume.
[0419] Taking this into account, a two-step working is selected similar to that in Example 1 (FIGS. 6 a, b). Preliminary preparation of the microstructure is effected at the first step. At the second step the structure is reduced to a preset grain size.
[0420] Like in Example 1, at the first step the billet is deformed by proportional two-component loading. Torsion is used as a primary component and tension is used as a secondary component. The ratio of the loading components at the working steps, the extent and rate of the deformation are taken the same as in Example 1.
[0421] The working of the thin-walled tubular billet is carried out jointly with a hollow sheath and a hollow core (FIG. 29) made of titanium alloy VT14 with a microcrystalline structure, having a mean grain size of d=1.0-2.0 microns, in two steps. The first step is carried out at a reduced temperature T=880° C., the second step at a temperature of 930° C.
[0422] The use of the hollow sheath and hollow core is necessary for preventing a loss of stability of the tubular billet at its deformation, particularly at the first step, as well as for increasing the efficiency of transformation of the structure of complication of the deformation scheme while preserving a simple loading scheme. Besides, the use of the sheath makes the stressed state scheme more favorable, i.e. conditions close to the uniform compression state are realized. At the same time, an increase of the plasticity resource is attained due to the exclusion of the deformation relief on the surface of the billet itself.
[0423] The sheath and core have the following dimensions.
[0424] The sheath: an internal diameter of 52.0 mm, a wall thickness of 5.0 mm, a length of 200.0 mm.
[0425] When the process of working is not associated with any significant change in the form of the billet, sheath and core, it is advisable to apply a layer of a separating material, for example, yttrium oxide, aluminum oxide, boron nitride, etc. on the internal surface of the core to facilitate the process of separation of the billet and core after the working.
[0426] Prior to the working, the billet is placed between the sheath and the core. Then the billet and core are heated to the first step temperature and deformed using the scheme and loading conditions of the first step.
[0427] Directly before the loading by the first step scheme, the billet and core are expanded to provide a uniform contact over the entire surface of the sheath, billet and core by supplying into the core space gaseous argon under pressure. The pressure is varied in a range of P=2.0-3.0 MPa.
[0428] It should be noted that during the process of working the whole assembly is deformed (sheath, billet and core).
[0429] After the first step the billet is cooled in air to room temperature. Then the billet is heated again to the second step temperature and is deformed by uniaxial tension.
[0430] Then the billet with the core are cooled to room temperature and disassemble. The sheath and core are removed by turning.
[0431] The metallographic analysis has shown that after this working, the billet has a uniform microcrystalline structure throughout the billet volume with a mean grain size of d=2.0-0.3 microns.
EXAMPLE 15[0432] Subjected to the working is a sheet billet of technically pure titanium of grade VT1-0 having a thickness of 2.0 mm.
[0433] It is necessary to obtain in the sheet billet a microcrystalline structure with a mean grain size of d=0.3-0.5 micron uniform throughout the billet volume.
[0434] The loading consists of intensive shift realized by torsion of the billet between a non-deformable sheath and non-deformable rod (FIG. 3O).
[0435] For this purpose, the billet is prepared by bending on three-roll sheet-bending machine by imparting a shape close to the shape of a pipe with the following dimensions: an external diameter of the pipe—50.0 mm, a height of the pipe—25.0 mm. A braze material based on Pb—Sn is applied onto the external and internal surfaces of the pipe by the vacuum deposition method. A core made of stainless steel with the billet preliminarily installed thereon is cooled liquid nitrogen and put into an assembled separable sheath also made of stainless steel and heated to a temperature of 250° C.
[0436] After the brazing, the assembly is cooled to room temperature and the billet deformed at a temperature of T=25° C. by turning the core and sheath relative to each other clockwise and counterclockwise at a speed of 0.1 to 0.5 rpm.
[0437] The extent of deformation per pass (a turn in one direction) is taken equal to 1.0. and y
[0438] The number of passes is taken equal to 10. After the working, the assembly is heated to a temperature of T=300° C., held at this temperature to complete the processes of re-crystallization and disassembled in a hot state.
[0439] The metallographic analysis has shown that after this working, the billet has a uniform microcrystalline structure throughout its volume with a mean grain size of d=0.3-0.6 microns.
EXAMPLE 16[0440] Subjected to the working are three thin-walled sheet billets made of titanium gamma aluminide (TiAl) using special pressing equipment (FIG. 31). The billets have the following dimensions: a thickness o 2.0 mm, a height of 25.0 mm, a width of 50.0 mm.
[0441] It is necessary to obtain in the billets a microcrystalline structure with a mean grain size of d=5.0- 10.0 microns uniform throughout the billet volume.
[0442] The billets are placed between the sheath and the core. They are heated to a temperature T=930° C. and deformed by applying an axial force to the sheath. In this case the core is stationary. This operation imparts to the billets a conical shape whose dimensions are closed to those of the working surface of the sheath and core.
[0443] The internal surface of the sheath and the external surface of the core are made conical with a cone angle of 30°. The contact surfaces of the sheath and core have notches along the radius and along the generating line of the cone in order to enhance the contact of the billet with the sheath and core. After the preliminary shaping operation the billets are cooled to room temperature and turned so that they form a conical unit with a minimum gaps between the elements.
[0444] It is well known that during the deformation of intermetallides of the Ti—Al system at a high temperature, for example, at 900-950° C. and higher under conditions of intensive slip of the processed billet along the surface of contact with the tool, titanium starts interact with nickel, which is an obligatory component of the composition of heat-resistant Ti—Ni alloys widely used in the machining tools. The interaction of Ti with Ni results in formation low-melting eutectic compounds leading to melting of the billet and the metal working equipment, development of processes of the so-called reactive braze material and formation of a compound between the billet and the tool. The application of lubricants does not prevent the formation of scratches. The example is deprived of this disadvantage, because there is no slip of the billet and the tool contact surface under high pressure since they are conical. Therefore, in this case it is possible to effectively use various layers not only as a material preventing development of diffusion processes on the contact surface but also as a means increasing the friction coefficient.
[0445] In this example, before assembly, the contact surfaces of the sheath and core are coated with an yttrium oxide emulsion in ethanol.
[0446] The billets are again placed between the sheath and the core, heated to a temperature of starting the working or T=950° C. and deformed. Directly before the working, the billet is tightly clamped between the conical sheath and the conical core and is deformed by shearing due to rotation of the sheath around the stationary core and, at the same, deforming it by compression by applying a constant axial force within 0.2-0.5 MN to the core. The deformation of the billet at the first step is carried out under isothermal conditions at T=950° C. At the second step the working is carried out with a temperature drop at the end of the working to T=750° C. At the first step the rate of the shear deformation is taken equal to 5.0×10−4 s−1 and a value of the accumulated deformation equal to e=2.5. The shear at the first and second steps is carried out by alternating rotation of the sheath and core relative to each other by the value of deformation intensity per turn ei=0.5. At the second step the billet is deformed using the scheme of the first step. The final value of the accumulated deformation is taken equal to 5.0. Having completed the working, the assembly is removed from the furnace and cooled in air to room temperature.
[0447] The metallographic analysis has shown that after this working, the billet has a uniform microcrystalline structure throughout its volume with a mean grain size equal to d=5.0-10.0 microns.
[0448] While preferred embodiments of the invention have been described, the present invention is capable of variation and modification and therefore should not be limited to the precise details of the Examples. The invention includes changes and alterations that fall within the purview of the following claims.
Claims
1. A multiple stage method for plastic working of a blank, comprising:
- applying a torsional loading to the blank at a first stage in multiple steps at loading conditions selected to effect microstructure transformation; and
- applying a tensile or compression loading at a second stage subsequent to the torsional loading stage.
2. The method of claim 1, wherein the steps and loading conditions are selected to effect microstructure transformation in the course of a heat-treatment between steps.
3. The method of claim 1, wherein the steps and loading conditions are selected to effect microstructure transformation in the course of a deforming selected from the torsional loading, tensile loading and compression loading.
4. The method of claim 1, comprising applying the loadings in a number of operating stages so that a microstructure transformation is provided at a first stage and a wrought layer deformation in a subsequent operating stage proceeds under conditions of superplasticity.
5. The method of claim 1, comprising selecting a number of operating stages and types of loadings according to a configuration of a primary blank, grain size of the primary blank and a desired configuration of a final blank.
6. The method of claim 1, comprising selecting a number of operating stages and types of loadings according to a preset grain size distribution over a blank cross-section.
7. The method of claim 1, comprising working a titanium blank at a deformation heat-treatment comprising cooling the blank until a temperature of a next step is attained that is equal to a temperature of a preceding step.
8. The method of claim 1, comprising working a titanium blank at a deformation heat-treatment comprising cooling the blank until a temperature of a next step is attained that is below a temperature of a preceding step followed by heating to the temperature of the next step.
9. The method of claim 1, comprising working a titanium blank at a deformation heat-treatment comprising cooling the blank to room temperature followed by heating to a temperature of a next step.
10. The method of claim 1, comprising working a titanium blank at deformation ratio and temperature-and-rate conditions selected to effect dynamic recrystallization in beta-phase and heat-treating to provide phase transformation, wherein the blank is heated to a temperature exceeding a temperature of blank working at a preceding step and subsequently cooling to a temperature of a next step.
11. The method of claim 1, comprising working a titanium blank at deformation ratio and temperature-and-rate conditions selected to effect static recrystallization in beta-phase, recrystallization annealing between steps and heat-treating to provide phase transformation, wherein the blank is heated to a temperature exceeding a temperature of blank working at a preceding step and subsequently cooling to a temperature of a next step.
12. The method of claim 1, comprising working the blank at a first stage deformation temperature and working the blank at a subsequent stage below the deformation temperature of the first stage.
13. The method of claim 1, comprising effecting deformation in two stages wherein, an amount of first stage deformation is selected to provide a value of microstructure reduction determined from the relationship
- 12 v 1 ≥ v 0 σ 2 ( σ 1 + σ 2 )
- where Vo is the volume of the entire blank;
- V1 is the volume of the transformed blank portion;
- &sgr;1 is the flow stress of a material having a microcrystalline structure;
- &sgr;2 is the flow stress of the material in the primary blank; furthermore, the temperature of a second stage is selected to be not in excess of the first deformation stage.
14. The method of claim 1, further comprising applying an axial loading component to the blank in at least a third stage.
15. The method of claim 1, wherein the blank is an axisymmetric blank in the shape of a rod having a cross-sectional dimension that is smaller than a preset grain size.
16. The method of claim 1, wherein the blank is a washer-shaped blank with a smaller height dimension than a preset grain size.
17. The method of claim 1, wherein the blank is a washer-shaped blank and the second stage comprises applying a uniaxial compression.
18. The method of claim 1, wherein the first stage comprises applying a compressional loading with the torsional loading.
19. The method of claim 1, wherein the first stage comprises applying a tension loading with the torsional loading.
20. The method of claim 1, wherein the first stage comprises alternately applying a torsion loading and an axial loading.
21. The method of claim 1, wherein the first stage comprises alternately applying a monotonic torsion loading and an axial loading.
22. The method of claim 1, wherein the first stage comprises alternately applying a torsion loading and a monotonic axial loading.
23. The method of claim 1, wherein the first stage comprises monotonic two-component loading wherein a ratio between an axial component of the loading force and the torsional component is not in excess of 0.2.
24. The method of claim 1, wherein the second stage comprises applying a combined compression and torsion loading.
25. The method of claim 1, wherein the second stage comprises applying a combined tension and torsion loading.
26. A multiple stage method for plastic working of a titanium blank, comprising:
- working a titanium blank by applying a torsional loading to the blank at a first stage in multiple steps at loading conditions selected to effect microstructure transformation; and applying a tensile or compression loading at a second stage subsequent to the torsional loading stage, wherein the working is at a deformation ration and under temperature-and-rate conditions selected to effect dynamic recrystallization in beta-phase; and
- heat treating to provide phase transformation.
27. The method of claim 26, comprising working a titanium blank at deformation ratio and temperature-and-rate conditions selected to effect static recrystallization in beta-phase, recrystallization annealing between steps and heat-treating to provide phase transformation.
28. The method of claim 26, comprising working a (&agr;+&bgr;) titanium blank, at a deformation temperature not exceeding [TAc3−(20÷30)]° C.
29. The method of claim 26, comprising working an alpha or pseudo-alpha titanium at a constant deformation temperature that ranges within TAc3+TAr3 for the titanium being worked.
30. The method of claim 26, comprising working a titanium blank at a deformation heat-treatment comprising cooling the blank at a specified rate that provides for a direct phase transformation according to a diffusion mechanism.
31. The method of claim 26, comprising working a titanium blank at a deformation heat-treatment comprising cooling the blank at a specified rate that is not in excess of martensite transformation in the beta-phase and corresponding to a maximum intensity of forming annealing twins in the alpha phase.
32. The method of claim 26, comprising working a titanium blank at a deformation heat-treatment comprising cooling the blank until the temperature of a next step is attained.
33. The method of claim 26, comprising working a titanium blank at a deformation heat-treatment comprising cooling the blank until the temperature of a next step is attained that is below the temperature of a preceding step.
34. The method of claim 26, comprising working a titanium blank at deformation ratio and temperature-and-rate conditions selected to effect dynamic recrystallization in beta-phase and heat-treating to provide phase transformation, wherein the blank is wrought at a variable temperature.
35. The method of claim 26, comprising working a titanium blank at deformation ratio and temperature-and-rate conditions selected to effect static recrystallization in beta-phase, recrystallization annealing between steps and heat-treating to provide phase transformation, wherein the blank is wrought at a variable temperature.
36. The method of claim 26, comprising working a (&agr;+&bgr;) titanium blank, at a deformation temperature not exceeding [TAc3−(20÷30)]° C., wherein the blank is wrought at a variable temperature.
37. The method of claim 26, comprising working a titanium blank having an original cast structure, comprising a first stage working preceded by a preconditioning step to provide dynamic recrystallization in the beta phase and heat-treating to cause reverse phase transformation.
38. A multiple stage method for plastic working of a blank, comprising:
- working the blank by applying a torsional loading to the blank at a first stage in multiple steps at loading conditions selected to effect microstructure transformation; and applying a tensile or compression loading at a second stage subsequent to the torsional loading stage,
- wherein the blank is deformed by working in a uniaxial tension sheath of a material, capable of undergoing superplastic deformation, wherein the sheath is in contact along the lateral surface of the blank to prevent displacement between the sheath and blank during working.
39. The method of claim 38, comprising placing the blank within a sheath capable of undergoing superplastic deformation, subjecting the sheath to uniaxial tensioning until a blank-to-sheath contact along a blank lateral surface is attained that prevents the sheath and blank from displacement relative to each other during the working.
40. The method of claim 38, comprising placing the blank within a sheath capable of undergoing superplastic deformation, subjecting the sheath to uniaxial tensioning until a blank-to-sheath contact along a blank lateral surface is attained that prevents the sheath and blank from displacement relative to each other and working the blank within the sheath according to said first and second stage.
41. The method of claim 38, wherein said blank is hollow and the method comprises placing a core within the blank and subjecting the blank and core to plastic deformation according to said first and second stage.
42. The method of claim 38, wherein said blank is hollow and the method comprises placing a core within the blank and subjecting the blank and core to plastic deformation according to said first and second stage, wherein said core comprises a material that is deformable under conditions of superplasticity at the plastic deformation temperature and rate.
43. The method of claim 38, wherein said blank is hollow and the method comprises placing a core within the blank and placing the blank and core within a sheath capable of undergoing superplastic deformation, subjecting the sheath to uniaxial tensioning until a blank-to-sheath contact along a blank lateral surface is attained that prevents the sheath and blank from displacement relative to each other and working the blank with core within the sheath according to said first and second stage.
44. The method of claim 38, wherein said blank is hollow and the method comprises placing a core of hollow construction within the blank and placing the blank and core within a sheath capable of undergoing superplastic deformation, subjecting the sheath to uniaxial tensioning until a blank-to-sheath contact along a blank lateral surface is attained that prevents the sheath and blank from displacement relative to each other and working the blank with core within the sheath according to said first and second stages.
45. The method of claim 38, wherein said blank is hollow and the method comprises placing a core of solid construction within the blank and placing the blank and core within a sheath capable of undergoing superplastic deformation, subjecting the sheath to uniaxial tensioning until a blank-to-sheath contact along a blank lateral surface is attained that prevents the sheath and blank from displacement relative to each other and working the blank with core within the sheath according to said first and second stages.
46. The method of claim 38, wherein said blank is hollow and the method comprises placing a core within the blank, expanding the core by pressure feeding of a working fluid into the core interior space and working the blank with core according to the first and second stages.
47. The method of claim 38, wherein said blank is hollow and the method comprises placing a core within the blank, interposing a material having viscous-flow properties between the blank and the core and working the blank with core according to the first and second stages.
48. The method of claim 38, wherein said blank is hollow and the method comprises placing a core within the blank, interposing a material having viscous-flow properties between the blank and the core and placing the blank, core and interposed material within a sheath capable of undergoing superplastic deformation, subjecting the sheath to uniaxial tensioning until a blank-to-sheath contact along a blank lateral surface is attained that prevents the sheath and blank from displacement relative to each other and working the blank with core within the sheath with interposed material according to said first and second stages.
49. The method of claim 38, wherein said blank is hollow and the method comprises placing a core within the blank, subjecting the blank and core to plastic deformation according to said first and second stage and expanding the blank by pressure-feeding a working fluid into a space between the blank and the core.
50. The method of claim 38, wherein said blank is hollow and the method comprises placing a core within the blank and placing the blank and core within a sheath capable of undergoing superplastic deformation, subjecting the sheath to uniaxial tensioning until a blank-to-sheath contact along a blank lateral surface is attained that prevents the sheath and blank from displacement relative to each other, working the blank with core within the sheath according to said first and second stage and expanding the blank within the sheath by pressure-feeding a working fluid into a space between the blank and the core.
51. The method of claim 38, wherein said blank is a hollow thin-walled blank comprising placing the blank within a sheath capable of undergoing superplastic deformation, subjecting the sheath to uniaxial tensioning until a blank-to-sheath contact along a blank lateral surface is attained that prevents the sheath and blank from displacement relative to each other during a process of working.
52. The method of claim 38, wherein said blank is hollow and the method comprises placing a core within the blank and placing the blank and core within a sheath capable of undergoing superplastic deformation, subjecting the sheath to uniaxial tensioning until a blank-to-sheath contact along a blank lateral surface is attained that prevents the sheath and blank from displacement relative to each other and working the blank by displacing the blank and the core relative to each other.
53. The method of claim 38, wherein said blank is hollow and the method comprises placing a core within the blank and placing the blank and core within a sheath capable of undergoing superplastic deformation, subjecting the sheath to uniaxial tensioning until a blank-to-sheath contact along a blank lateral surface is attained by a brazed joint that prevents the sheath and blank from displacement relative to each other, working the blank with core within the sheath according to said first and second stage and expanding the blank within the sheath by pressure-feeding a working fluid into a space between the blank and the core.
54. The method of claim 38, wherein said blank is hollow and the method comprises placing a core within the blank and placing the blank and core within a sheath capable of undergoing superplastic deformation, subjecting the sheath to uniaxial tensioning until a blank-to-sheath contact along a blank lateral surface is attained by a brazed joint that prevents the sheath and blank from displacement relative to each other, working the blank with core within the sheath according to said first and second stage and expanding the blank within the sheath by pressure-feeding a working fluid into a space between the blank and the core, wherein an initial thickness &Dgr; of a brazing solder interlayer is such that &Dgr;≦0.005 t, where t is thickness of the blank.
55. The method of claim 38, wherein the blank is a plate interposed between a sheath and a rod, wherein contact there between is provided by prestraining the plate, and displacing the sheath and the rod relative each other in the course of working of the blank.
56. The method of claim 38, wherein the blank is a plate interposed between a conical sheath and a conical rod, wherein contact there between is provided by prestraining the plate during assembly, and displacing the sheath and the rod relative each other in the course of working of the blank.
57. The method of claim 38, wherein the blank is a plate interposed between a conical sheath and a conical rod, wherein contact there between is provided by prestraining the plate during assembly, and displacing the sheath and the rod relative each other in the course of working of the blank comprising applying a uniform deforming force to an end face of the blank over an area having radius r equal to 0.7<r<R, where R is the radius of the blank being worked.
58. A multiple stage method for plastic working of a blank, comprising:
- deforming by working the blank by applying a torsional loading to the blank at a first stage in multiple steps at loading conditions selected to effect microstructure transformation; and applying a tensile or compression loading at a second stage subsequent to the torsional loading stage,
- wherein a deforming force is imparted to the blank through an inseparable joint with a tool.
59. The method of claim 58, wherein a deforming force is imparted to the blank through an inseparable fusion welded joint.
60. The method of claim 58, wherein a deforming force is imparted to the blank through an inseparable solid-phase welded joint.
61. The method of claim 58, wherein a deforming force is imparted to the blank through an inseparable brazed joint.
62. The method of claim 58, wherein a deforming force is imparted to the blank through an inseparable brazed joint, wherein the joint is formed with a brazing solder having a melting point that exceeds the temperature of working the blank.
63. The method of claim 58, wherein a deforming force is imparted to the blank through an inseparable brazed joint, wherein the joint is formed with a brazing solder having a melting point that exceeds the temperature of working the blank, wherein the joint thickness is (0.005÷0.01)D, where D is the transverse dimension of the joint.
64. A method for plastic working of blanks, comprising:
- determining deformation accumulated in working a blank;
- determining depth of a layer of the blank being wrought;
- determining the plasticity reserve of the blank being wrought;
- and further applying a number of deformation steps to the blank according to the determined accumulated deformation, layer depth and plasticity reserve.
65. An article, comprising:
- a hollow blank with a hollow core emplaced within the blank and expanded by pressurized fluid contained within the core interior and a sheath encompassing the blank in a blank to sheath contact along a blank lateral surface that prevents the sheath and blank from displacement relative to each other.
66. The article of claim 65, further comprising a viscous flow material between the blank and the core.
Type: Application
Filed: Jan 9, 2003
Publication Date: Jul 15, 2004
Inventors: Oskar Akramovich Kaibyshev (Ufa), Valeriy Kuzmich Berdin (Ufa)
Application Number: 10338683
