OXIDE-DISPERSION-STRENGTHENED ALLOY
The present invention provides an oxide dispersion strengthened alloy in which even with aluminum contained, the particle diameter and dispersion spacing of the oxide are decreased, and the strength at high temperature, the high temperature oxidation and the corrosion resistance can be improved. An oxide dispersion strengthened alloy being a nickel-base alloy containing aluminum, hafnium, and yttrium oxide, wherein a complex oxide of the yttrium oxide and hafnium oxide is dispersed in a matrix of the nickel-base alloy, with the aluminum contained.
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This application is a U.S. national application of PCT International Application PCT/JP2009/064410, filed Aug. 17, 2009, which claims priority to Japanese Application No. 2008-212185, filed Aug. 20, 2008, the contents of each of which are incorporated by reference in their entirety for all purposes.
FIELD OF THE INVENTIONThe present invention relates to an oxide dispersion strengthened alloy and particularly to an oxide dispersion strengthened alloy that is preferred as a material for the rotor blade or stator blade of a gas turbine, a high temperature heating furnace member, or the like used at high temperature.
BACKGROUND OF THE INVENTIONConventionally, the research and development of materials called oxide dispersion strengthened (hereinafter referred to as “ODS”) alloys, as high temperature-resistant materials used for gas turbines and the like, have been performed. For these ODS alloys, an alloy powder and an oxide powder are subjected to mechanical alloying treatment by a ball mill, and then, particles of an oxide, such as yttrium oxide, are finely dispersed in a base material, such as nickel, by annealing treatment so as to improve high temperature strength.
As such an ODS alloy, for example, an ODS alloy described in Japanese Patent Laid-Open No. 7-90438 is proposed (Patent Literature 1). This ODS alloy comprises 2% or less of one or more elements selected from the group consisting of titanium, zirconium, and hafnium, 15 to 35% of chromium, 0.01 to 0.4% of carbon, and 0.1 to 2.0% of an oxide comprising yttrium, by weight, and the remainder substantially comprising nickel, and is formed by dispersing an oxide comprising yttrium, as particles, in the matrix of a nickel-base alloy containing one or more elements selected from the group consisting of titanium, zirconium, and hafnium, chromium, and carbon.
SUMMARY OF THE INVENTIONHowever, in the invention described in Patent Literature 1, aluminum is excluded from the alloy composition, focusing on the problem that when a complex oxide of aluminum oxide and yttrium oxide is formed, the oxide particles are coarsened, and the high temperature strength decreases. Therefore, a problem of the above Patent Literature 1 is that a positive effect of the addition of aluminum on an ODS alloy, that is, the effect of improving high temperature oxidation and corrosion resistance, is not obtained.
In other words, it is known that in an ODS alloy containing aluminum, the high temperature oxidation and the corrosion resistance are improved by the action of the aluminum. Therefore, there is a high practical demand to add aluminum to an ODS alloy. On the other hand, a problem is that in the presence of aluminum having low oxide formation energy, aluminum oxide forms a complex oxide with yttrium oxide, decreasing the high temperature strength, as pointed out in Patent Literature 1,
In addition, in a nickel-based ODS alloy, the so-called gamma prime (y′) phase is precipitated, depending on the content of aluminum. This gamma prime phase has a property that as the temperature increases, the yield strength increases, but a problem of this gamma prime phase is that at a high temperature of 900° C. or more, it dissolves, and therefore, the high temperature strength decreases. Conventional ODS alloys are put to practical use for high temperature members, such as gas turbine blades, but a decrease in strength occurs at a high temperature of 900° C. or more, as described above, and therefore, the situation is that the limit point is set in the temperature range. This is an important problem to be solved, particularly in industries where more efficient energy conservation has been required in recent years.
On the other hand, it is known that in a nickel-based ODS alloy, yttrium oxide particles govern high temperature strength at 1000° C. or more. However, the yttrium oxide particles have an average particle diameter of about 16 nm and are relatively coarse. In addition, it is known that when yttrium oxide forms a complex oxide with aluminum oxide, the oxide particles are coarsened. Therefore, a problem of conventional ODS alloys is that the effect of improving high temperature strength by the dispersion of oxide particles is not sufficiently obtained.
In the invention in Patent Literature 1, it is described that by adding 2.0 wt % or less of titanium oxide, zirconium oxide, or hafnium oxide, a complex oxide with yttrium oxide is formed. But, in addition to containing no aluminum, actually, only experiments in which the amount of zirconium oxide and hafnium oxide added is 0.05 wt % and 0.30 wt % respectively are performed, and moreover, their creep rupture strength at 900° C. is considerably lower, compared with other test pieces, and only a lower result is obtained, even compared with nickel-based ODS alloys, such as MA6000 (Special Metals Corporation) and TMO-2 (National Institute for Materials Science), put to practical use.
The present invention has been made to solve such problems, and it is an object of the present invention to provide an oxide dispersion strengthened alloy in which even with aluminum contained, the particle diameter and dispersion spacing of the oxide are decreased, and the strength at high temperature, the high temperature oxidation and the corrosion resistance can be improved.
An oxide dispersion strengthened alloy according to the present invention is a nickel-base alloy containing aluminum, hafnium, and yttrium oxide, wherein a complex oxide of the yttrium oxide and hafnium oxide is dispersed in a matrix of the nickel-base alloy, with the aluminum contained.
In addition, in the present invention, the complex oxide may have an average particle diameter of 7 to 11 nm and an average dispersion spacing of 47 to 97 nm.
In addition, in the present invention, less than 2% of an aluminum element, 0.4 to 3.2% of a hafnium element, and 0.5 to 2.0% of yttrium oxide by weight may be contained.
Further, in the present invention, the ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide may be 1:0.5 to 1:4.
In addition, in the present invention, 0.5% of an aluminum element, 0.8% of a hafnium element, and 1% of yttrium oxide by weight may be contained.
Further, in the present invention, the ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide may be 1:1.
In addition, in the present invention, 26% or less by weight of one or two or more elements selected from the group consisting of chromium, titanium, tantalum, tungsten, molybdenum, iron, zirconium, carbon, and boron may be further contained.
According to the present invention, even with aluminum contained, the particle diameter and dispersion spacing of the oxide are decreased, and the strength at high temperature, the high temperature oxidation and the corrosion resistance can be improved.
The present inventors have repeated trial and error and studied diligently in order to solve the above-described problems, and, as a result, found that the above-described problems can be solved by an oxide dispersion strengthened alloy being a nickel-base alloy containing aluminum, hafnium, and yttrium oxide, wherein a complex oxide of the above yttrium oxide and hafnium oxide is formed and dispersed in the matrix of this nickel-base alloy, with the aluminum contained.
First, the basic principle of the present invention will be described. It is found that in an ODS alloy, in a case where the volume fraction f of the oxide particles is fixed, as the radius r of the oxide particles is decreased, the dispersion spacing ls of the oxide particles decreases proportionally, as shown in the following formula (1).
lsβ(r/√f) formula (1)
wherein β is a constant.
In addition, the yield stress σ of the ODS alloy increases in inverse proportion to the dispersion spacing ls of the oxide particles, as shown in the following formula (2).
σ ∝ l/ls formula (2)
Therefore, it is found that as the size of the oxide particles decreases, the yield stress σ of the ODS alloy is improved inversely proportionally, as shown in the following formula (3) obtained from the above formulas (1) and (2).
σ ∝(√f/r) formula (3)
From the above, it is found that when a nickel-based ODS alloy containing oxide particles smaller than oxide particles that conventional nickel-based ODS alloys put to practical use contain can be manufactured, an ODS alloy having higher yield stress is obtained. Specifically, adding an element that has a lower free energy of oxide formation (forms an oxide more easily) and a smaller diffusion coefficient than aluminum has been conceived as a method for suppressing the growth and coarsening of yttrium oxide.
In the present invention, hafnium (Hf) has been selected as an element that satisfies the above conditions, based on the relationship between the free energy of oxide formation and diffusion ability of alloy elements shown in
The function of each element contained in an oxide dispersion strengthened alloy according to the present invention will be described below.
Aluminum (Al) is an element that is effective for improving high temperature oxidation and corrosion resistance. In addition, aluminum is an element that causes a gamma prime (γ′) phase to be precipitated in the matrix of a nickel-base alloy, depending on the amount of aluminum added. In this embodiment, by adding aluminum in a range in which this gamma prime phase is not precipitated, dispersion strengthening by oxide particles is intended, while the high temperature oxidation and the corrosion resistance are maintained.
Yttrium oxide (Y2O3) is dispersed in the matrix of a nickel-base alloy and improves strength particularly in a high temperature environment at more than about 900° C. If the content of yttrium oxide is less than 0.5 wt %, sufficient high temperature strength may not be obtained. On the other hand, if the content of yttrium oxide is more than 2.0 wt %, the ductility and the working and forming properties may degrade significantly. Therefore, the content of yttrium oxide is preferably selected in the range of 0.5 to 2.0 wt %. In this embodiment, 1 wt % is selected, but the content of yttrium oxide is not limited to this, and may be appropriately changed and selected in a range in which a preferred effect of yttrium oxide is obtained, and in a range in which the demerit is acceptable.
Hafnium (Hf) serves the function of suppressing the growth and coarsening of yttrium oxide particles. In this embodiment, hafnium forms a complex oxide with yttrium oxide in the form of hafnium oxide (HfO2). Therefore, yttrium oxide is prevented from forming a complex oxide with aluminum oxide (Al2O3), and the particle diameter and dispersion spacing of the oxide particles are small.
In this embodiment, the amount of hafnium added is selected so that the ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide is 1:0.5 to 1:4 in order to effectively form a complex oxide of yttrium oxide and hafnium oxide. More preferably, the amount of hafnium added is preferably such that the ratio of the number of molecules is 1:1. However, the amount of hafnium added is not limited to this, and the amount of hafnium formulated may be appropriately changed and selected as long as the dispersion spacing of the above complex oxide can be decreased to maintain high temperature strength.
Next, a method for manufacturing the oxide dispersion strengthened alloy in this embodiment will be described.
First, in addition to a nickel powder that is a matrix, predetermined amounts of aluminum, hafnium, and yttrium oxide powders that are basic components are formulated. At this time, when aluminum is added at an added weight at which the gamma prime phase is not precipitated, the gamma prime phase is not precipitated, and dispersion strengthening by the oxide phase alone is intended.
Next, the formulated mixed powders are introduced into a planetary ball mill, and mechanical alloying treatment is performed. This mechanical alloying treatment is treatment in which the collision energy of balls provided in the planetary ball mill is used to repeatedly cause the folding and rolling of the powders for alloying. By this mechanical alloying treatment, the mixed powders are alloyed on the atomic order even under room temperature conditions.
Then, the alloyed mixed powders are sintered by hot pressing. At this time, aluminum and hafnium are each oxidized, and aluminum oxide and hafnium oxide are each formed, and the above hafnium oxide forms a complex oxide with yttrium oxide. Thus, the complex oxide is finely dispersed in the matrix of the nickel-base alloy, and the growth and coarsening of the oxide particles are suppressed. Therefore, the size and dispersion spacing of the oxide particles decrease, and the yield stress of the oxide dispersion strengthened alloy itself is improved.
When the stator blade of a gas turbine is manufactured using the oxide dispersion strengthened alloy in this embodiment, it is possible to form a blade shape from an ingot after final heat treatment by machining. In addition, when a combustor liner and a transition piece are manufactured, it is possible to repeat hot rolling to make a thin plate, then hot-work the thin plate into a cylindrical shape, and then perform heat treatment. In addition, when a cylinder without a joining portion is manufactured, it is possible to hollow the central portion of a cylindrical ingot to make a thick cylinder, and perform hot ring rolling.
According to this embodiment as described above, such effects are achieved that even with aluminum contained, the particle diameter and dispersion spacing of the oxide are decreased, and the strength at high temperature, the high temperature oxidation and the corrosion resistance can be improved, and the like.
EXAMPLESNext, Examples of the oxide dispersion strengthened alloy according to the present invention will be described. Specifically, in order to confirm a preferred content of the oxide dispersion strengthened alloy according to the present invention and its effect, oxide dispersion strengthened alloys having various formulation components shown in
In these Examples, in the manufacture of the oxide dispersion strengthened alloys with formulation amounts allocated, mechanical alloying treatment was performed using a planetary ball mill (manufactured by Fritsch). For the treatment conditions, the number of revolutions of the ball mill was 400 rpm, and the treatment time was 24 hours, at room temperature in an Ar gas atmosphere. Then, at a temperature of 1200° C., hot pressing under a load of 1 ton for 3 hours was performed for sintering.
In the measurement of the average particle diameter and the average dispersion spacing, the sintered sample was cut, then a thin film sample was fabricated by electropolishing, and the oxide particles were observed using a transmission electron microscope (JEL-2000EX/T: manufactured by JEOL Ltd.). The complex oxide particles in these Examples are present in a polygonal shape or an elliptical shape, to be exact, but they are in a range in which they can be approximated by a circular shape. Therefore, in these Examples, each particle in images obtained by the transmission electron microscope was approximated by a circular shape, and the average particle diameter and the average dispersion spacing were calculated by statistical processing and analysis. Specifically, from four TEM (Transmission Electron Microscope) photographs having a field-of-view size of about 300 μm×300 μm, statistical processing and analysis with circle approximation were performed using image processing software (Mac-view: manufactured by Mountech Co., Ltd.).
In addition, for the yield stress, the yield stress at 1000° C. was tentatively calculated according to a void strengthening theory based on the above formula (3). For the measurement of the Vickers hardness, the Vickers hardness was measured under a load of 1 kg at room temperature, using a Vickers hardness tester (Micro Vickers: manufactured by SHIMADZU CORPORATION).
Comparative Example 1First, various properties were measured for a nickel-based ODS alloy put to practical use (PM1000: manufactured by PLANSEE) as Comparative Example 1. This PM1000 is a nickel-base alloy and contains 0.6 wt % of yttrium oxide, 0.3 wt % of aluminum, and, in addition, 23.5 wt % of chromium and the like.
As shown in
Next, as Comparative Example 2, the present inventors manufactured a nickel-based oxide dispersion strengthened alloy containing no hafnium and aluminum. Specifically, 1 wt % of yttrium oxide was contained in a nickel-base alloy.
As shown in
As Comparative Example 3, the present inventors manufactured a nickel-based oxide dispersion strengthened alloy containing no hafnium. Specifically, 1 wt % of yttrium oxide and 0.5 wt % of aluminum were contained in a nickel-base alloy.
As shown in
As described above, in the ODS alloys of Comparative Example 2 and Comparative Example 3 containing only the basic components, the diameter of the oxide particles is almost equal to that of Comparative Example 1 put to practical use. According to the results of the Comparative Examples described above, it was confirmed that in the simple basic components, the formation of oxide particles in a nickel-based ODS alloy was appropriately reproduced.
Example 1Next, as Example 1, one obtained by further adding hafnium to the formulation of Comparative Example 3, that is, a nickel-based ODS alloy containing aluminum, hafnium, and yttrium oxide was manufactured. Specifically, 1 wt % of yttrium oxide, 0.5 wt % of aluminum, and 0.8 wt % of hafnium were contained in a nickel-base alloy.
The amount of hafnium added was determined so that the ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide was 1:1 in order to effectively form a complex oxide of yttrium oxide (Y2O3) and hafnium oxide (HfO2).
As shown in
In addition, in the sample of this Example 1, the electron beam diffraction spots obtained from the oxide particles match the diffraction spots of Y2Hf2O7 that is a complex oxide of yttrium oxide and hafnium oxide, and the oxide particles in the ODS alloy of this Example 1 are of a complex oxide of yttrium oxide and hafnium oxide.
According to this Example 1 as described above, it was shown that by the addition of hafnium, even with aluminum oxide contained, yttrium oxide forms a complex oxide with hafnium oxide and is dispersed in the matrix of a nickel-base alloy. In addition, it was shown that by the addition of hafnium, the average particle diameter and average dispersion spacing of the oxide particles are minimized, and the yield stress and Vickers hardness of the ODS alloy are improved.
Example 2In Example 2, the amount of hafnium added was reduced with respect to the formulation of Example 1, and a nickel-based ODS alloy containing aluminum, hafnium, and yttrium oxide was manufactured. Specifically, 1 wt % of yttrium oxide, 0.5 wt % of aluminum, and 0.4 wt % of hafnium were contained in a nickel-base alloy. The amount of hafnium added was determined so that the ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide was 1:0.5.
As shown in
According to this Example 2 as described above, it was shown that even if the amount of hafnium added, with respect to 1 wt % of yttrium oxide, is 0.4 wt %, the average particle diameter and average dispersion spacing of the oxide particles are reduced, and the yield stress and Vickers hardness of the ODS alloy are improved.
Example 3In Example 3, the amount of hafnium added was increased with respect to the formulation of Example 1, and a nickel-based ODS alloy containing aluminum, hafnium, and yttrium oxide was manufactured. Specifically, 1 wt % of yttrium oxide, 0.5 wt % of aluminum, and 1.6 wt % of hafnium were contained in a nickel-base alloy. The amount of hafnium added was determined so that the ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide was 1:2.
As shown in
According to this Example 3 as described above, it was shown that even if the amount of hafnium added, with respect to 1 wt % of yttrium oxide, is 1.6 wt %, the average particle diameter and average dispersion spacing of the oxide particles are reduced, and the yield stress and Vickers hardness of the ODS alloy are improved.
Example 4Next, in Example 4, the amount of aluminum added was increased with respect to the formulation of Example 1, and a nickel-based ODS alloy containing aluminum, hafnium, and yttrium oxide was manufactured. Specifically, 1 wt % of yttrium oxide, 4.5 wt % of aluminum, and 0.8 wt % of hafnium were contained in a nickel-base alloy. The amount of aluminum added was determined, based on the aluminum content of MA6000 (Special Metals Corporation) that was a gamma prime precipitation strengthened alloy, among ODS alloys put to practical use.
In addition, in this Example 4, 25.71 wt % of one or two or more elements selected from the group consisting of chromium, titanium, tantalum, tungsten, molybdenum, iron, zirconium, carbon, and boron were contained. Chromium is effective for the improvement of oxidation resistance and corrosion resistance. Titanium and tantalum are effective for the stabilization of the gamma prime phase. Tungsten, iron, and molybdenum are effective as a solid solution strengthening element. Carbon, boron, and zirconium are effective in strengthening grain boundaries.
As shown in
According to this Example 4 as described above, it was shown that in a case where aluminum is contained at an added weight at which the gamma prime phase is precipitated, even if 0.8 wt % of hafnium is added, the growth and coarsening of the oxide particles are not sufficiently suppressed, and the average particle diameter and the average dispersion spacing cannot be minimized, and therefore, the yield stress of the ODS alloy also cannot be improved.
Example 5Next, in Example 5, the amount of hafnium added was further reduced with respect to the formulation of Example 2, and a nickel-based ODS alloy containing aluminum, hafnium, and yttrium oxide was manufactured. Specifically, 1 wt % of yttrium oxide, 0.5 wt % of aluminum, and 0.08 wt % of hafnium were contained in a nickel-base alloy. The amount of hafnium added was determined so that the ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide was 1:0.1.
As shown in
According to this Example 5 as described above, it was shown that although 0.08 wt % of hafnium is added with respect to 1 wt % of yttrium oxide, the average particle diameter and average dispersion spacing of the oxide particles are not so small, and the yield stress and Vickers hardness of the ODS alloy are not improved.
Example 6In Example 6, the amount of hafnium added was further increased with respect to the formulation of Example 3, and a nickel-based ODS alloy containing aluminum, hafnium, and yttrium oxide was manufactured. Specifically, 1 wt % of yttrium oxide, 0.5 wt % of aluminum, and 3.2 wt % of hafnium were contained in a nickel-base alloy. The amount of hafnium added was determined so that the ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide was 1:4.
As shown in
According to this Example 6 as described above, it was shown that although the amount of hafnium added, with respect to 1 wt % of yttrium oxide, is 3.2 wt %, the average particle diameter and average dispersion spacing of the oxide particles are minimized, and the yield stress and Vickers hardness of the ODS alloy are improved.
Example 7In Example 7, the amount of hafnium added was increased with respect to the formulation of Example 4, and a nickel-based ODS alloy containing aluminum, hafnium, and yttrium oxide was manufactured. Specifically, 1 wt % of yttrium oxide, 4.5 wt % of aluminum, and 5 wt % of hafnium were contained in a nickel-base alloy. This is to check whether there is an improvement in average dispersion spacing and yield stress at 1000° C. by increasing the amount of hafnium even if the content of aluminum is increased. In addition, as in Example 4, 25.71 wt % of one or two or more elements selected from the group consisting of chromium, titanium, tantalum, tungsten, molybdenum, iron, zirconium, carbon, and boron were contained.
As shown in
According to this Example 7 as described above, in a case where aluminum was contained at an added weight at which the gamma prime phase was precipitated, by adding 5 wt % of hafnium, the average particle diameter and average dispersion spacing of the oxide particles decreased slightly, and an improvement was also seen in the yield stress at 1000° C. of the ODS alloy.
Example 8In Example 8, in order to clarify the effect of the aluminum content, the amount of aluminum added was made larger than that of Example 1 and smaller than that of Example 4, and a nickel-based ODS alloy containing aluminum, hafnium, and yttrium oxide was manufactured. Specifically, 1 wt % of yttrium oxide, 2 wt % of aluminum, and 0.8 wt % of hafnium were contained in a nickel-base alloy. For the amount of hafnium and yttrium oxide formulated, Example 1 with the best effect was referred to. The amount of aluminum added was determined so that the weight ratio of hafnium to aluminum was 0.8:2.
As shown in
According to this Example 8 as described above, it is found that when 2 wt % of aluminum is contained in 1 wt % of yttrium oxide and 0.8 wt % of hafnium, some improvement effect is seen, in view of the balance between aluminum and hafnium, but cannot be said to be sufficient.
Example 9In Example 9, in order to clarify the effect of the aluminum content as in Example 8, the amount of aluminum added was made larger than that of Example 8, and a nickel-based ODS alloy containing aluminum, hafnium, and yttrium oxide was manufactured. Specifically, 1 wt % of yttrium oxide, 4 wt % of aluminum, and 0.8 wt % of hafnium were contained in a nickel-base alloy. The amount of aluminum added was determined so that the weight ratio of hafnium to aluminum was 0.8:4.
As shown in
According to this Example 9 as described above, it was shown that in a case where 4 wt % of aluminum is contained in 1 wt % of yttrium oxide, even if 0.8 wt % of hafnium is added, the average particle diameter and average dispersion spacing of the oxide particles are not minimized, and the yield stress of the ODS alloy is not improved.
Here, the dependence of various properties on hafnium concentration is considered for Comparative Example 3 and Examples 1 to 3, 5, and 6 containing 0.5 wt % of aluminum and 1 wt % of yttrium oxide, among the above Examples.
As shown in
Next, in order to consider the dependence on aluminum concentration, the data of Examples 8 and 9 in which the aluminum concentration is increased with respect to the formulation of Example 1 are shown in
As shown in
From the above, it was shown that the high temperature strength, the high temperature oxidation and the corrosion resistance can be improved by an oxide dispersion strengthened alloy containing less than 2 wt %, an added weight at which the gamma prime phase is not precipitated, of an aluminum element, 0.4 to 3.2 wt % of a hafnium element, and 1 wt % of yttrium oxide. In addition, in this oxide dispersion strengthened alloy, the ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide is 1:0.5 to 1:4.
Further, it was shown that the high temperature strength, the high temperature oxidation and the corrosion resistance can be most improved by an oxide dispersion strengthened alloy containing 0.5 wt % of an aluminum element, 0.8 wt % of a hafnium element, and 1 wt % of yttrium oxide. In addition, in this oxide dispersion strengthened alloy, the ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide is 1:1.
In addition, 26 wt % or less of one or two or more elements selected from the group consisting of chromium, titanium, tantalum, tungsten, molybdenum, iron, zirconium, carbon, and boron may be contained, as in the above Examples 4 and 7. It is considered that this secondarily improves the high temperature strength, the high temperature oxidation and the corrosion resistance, and the like.
Further, from the results of the above Examples, it was shown that the high temperature strength, the high temperature oxidation and the corrosion resistance can be improved by an oxide dispersion strengthened alloy in which a complex oxide of yttrium oxide and hafnium oxide has an average particle diameter of 7 to 11 nm and an average dispersion spacing of 47 to 89 nm.
In addition, as shown in
In Example 10, a nickel-based ODS alloy having a composition similar to that of the alloy put to practical use (PM1000: manufactured by PLANSEE) used in the above Comparative Example 1 was fabricated, and the effect of the addition of hafnium was verified together. Specifically, as the nickel-based ODS alloy corresponding to the alloy put to practical use, 0.6 wt % of yttrium oxide and 0.3 wt % of aluminum were contained in a nickel-base alloy. In addition, 0.5 wt % of hafnium was further contained in this alloy.
For the fabrication method, the element powders were mixed, and then, mechanical alloying (MA) treatment was performed in an Ar gas atmosphere, using the planetary ball mill, for 24 hours. Then, the MA powder was consolidated and formed by hot pressing (1200° C., 10 kN, 3 hours), also for the precipitation treatment of the oxide particles. The consolidated and formed sample was cut, then a thin film sample was fabricated by electropolishing, and the oxide particles were observed using the transmission electron microscope (TEM).
As shown in
In this Example 10, the content of yttrium oxide is 0.6 wt %, and the content of hafnium is 0.5 wt %, and therefore, the ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide is equal to 1:1. In addition, it is considered that the average dispersion spacing is larger, compared with the above-described other Examples because the content of yttrium oxide in other Examples is 1 wt %, whereas in this Example 10, the content of yttrium oxide is as low as 0.6 wt %, and the volume fraction of yttrium oxide is small.
According to this Example 10 as described above, it was confirmed that also for an alloy corresponding to a nickel-based ODS alloy put to practical use, the addition of hafnium is effective in making the oxide particles finer and narrowing the average dispersion spacing. In addition, it was shown that the yield stress and Vickers hardness of the ODS alloy are improved.
Further, from the results of the above Examples 1 to 3, 6, and 10, it was shown that the high temperature strength, the high temperature oxidation and the corrosion resistance can be improved by an oxide dispersion strengthened alloy in which a complex oxide of yttrium oxide and hafnium oxide has an average particle diameter of 7 to 11 nm and an average dispersion spacing of 47 to 97 nm.
Example 11In this Example 11, for the nickel-base alloy (Ni-0.5Al-0.8Hf-1Y2O3) manufactured in the above Example 1, an experiment for identifying the oxide particles that were made finer was performed. Specifically, an X-ray diffraction test was performed on the sample obtained by solidifying the mechanically alloyed powder of the nickel-base alloy by hot pressing, manufactured in the above Example 1. The result is shown in
As shown in
The oxide dispersion strengthened alloy according to the present invention is not limited to the above-described embodiment and Examples, and can be appropriately changed.
Claims
1. An oxide dispersion strengthened alloy being a nickel-base alloy comprising aluminum, hafnium, and yttrium oxide, wherein a complex oxide of the yttrium oxide and hafnium oxide is dispersed in a matrix of the nickel-base alloy, with the aluminum contained.
2. The oxide dispersion strengthened alloy according to claim 1, wherein the complex oxide has an average particle diameter of 7 to 11 nm and an average dispersion spacing of 47 to 97 nm.
3. The oxide dispersion strengthened alloy according to claim 1, comprising less than 2% of an aluminum element, 0.4 to 3.2% of a hafnium element, and 0.5 to 2.0% of yttrium oxide by weight.
4. The oxide dispersion strengthened alloy according to claim 1, wherein a ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide is 1:0.5 to 1:4.
5. The oxide dispersion strengthened alloy according to claim 3, comprising 0.5% of an aluminum element, 0.8% of a hafnium element, and 1% of yttrium oxide by weight.
6. The oxide dispersion strengthened alloy according to claim 4, wherein the ratio of the number of molecules of yttrium oxide to the number of molecules of hafnium oxide is 1:1.
7. The oxide dispersion strengthened alloy according to claim 1, further comprising 26% or less by weight of one or two or more elements selected from the group consisting of chromium, titanium, tantalum, tungsten, molybdenum, iron, zirconium, carbon, and boron.
Type: Application
Filed: Aug 17, 2009
Publication Date: Jun 16, 2011
Applicant: NATIONAL UNIVERSITY CORPORATION HOKKAIDO UNIVERSITY (Hokkaido)
Inventors: Shigeharu Ukai (Hokkaido), Soumei Oonuki (Hokkaido), Shigenari Hayashi (Hokkaido), Takeshi Hoshino (Hokkaido)
Application Number: 13/059,774