Amorphous alloy excelling in fatigue strength
An amorphous alloy having a composition represented by the general formula: XaMbAlc (wherein X represents at least one element selected from the group consisting of Zr and Hf, M represents at least one element selected from the group consisting of Ni, Nb, Cu, Fe, Co, and Mn, and a, b, and c represent such atomic percentages as respectively satisfy 25≦a≦85, 5≦b≦70, and 0<c≦35) and containing an amorphous phase in the range of 50-100% in a volumetric ratio contains hydrogen incorporated therein. Preferably the hydrogen is present in the amorphous alloy in an amount of 0.005-10% of the amorphous alloy in a weight ratio.
1. Field of the Invention
This invention relates to an amorphous alloy which exhibits high hardness and high strength, excels in working characteristics, has high resistance to corrosion and high fatigue strength, and further excels in vibration-damping properties.
2. Description of the Prior Art
Since an amorphous alloy being also called metal glass generally has such higher strength as the tensile strength about 3 times of a stainless steel and about twice of a titanium alloy and exhibits high resistance to corrosion and low Young's modulus, it has become of major interest as an industrial material.
Among the amorphous alloys heretofore known in the art, the amorphous alloys of Zr,Hf-M-Al system (M=Ni, Cu, Fe, Co, Mn) having a wide temperature width of a supercooled liquid region, which is a temperature width between a glass transition temperature (Tg) and a crystallization temperature (Tx), and excelling in various properties such as high hardness, high strength, high heat resistance, and high corrosion resistance are known as the amorphous alloys having excellent working characteristics (for example, see JP 3-158446,A).
However, the above-mentioned amorphous alloys and the metal glass which is now generally studied exhibit low fatigue strength and thus are not suitable as a material which is used in a place to be subjected to repeated stress for a long period of time. Further, since the metal glass is microscopically a non-defective material containing therein no “dislocation” or the like defects which are contained in a common crystalline metal, once vibration is applied to the material, the vibration will continue for a long period of time because the vibration will not be obstructed by “dislocation” etc. That is, the metal glass has such a problem that the “vibration-damping properties” thereof are poor.
SUMMARY OF THE INVENTIONIt is, therefore, an object of the present invention to provide amorphous alloys which, while retaining the excellent properties of the above-mentioned Zr-based and Hf-based amorphous alloys of exhibiting high hardness and high strength, excelling in working characteristics, and having high corrosion resistance, further exhibit improved fatigue strength and excel in the vibration-damping properties.
To accomplish the object mentioned above, the present invention provides an amorphous alloy having a composition represented by the following general formula and containing an amorphous phase in a volumetric ratio of 50-100%, characterized in that it contains hydrogen incorporated therein:
XaMbAlc
wherein X represents at least one element selected from the group consisting of Zr and Hf, M represents at least one element selected from the group consisting of Ni, Nb, Cu, Fe, Co, and Mn, and a, b, and c represent such atomic percentages as respectively satisfy 25≦a≦85, 5≦b≦70, and 0<c≦35.
Since the amorphous alloy of the present invention uses as a base material the amorphous alloy having the composition represented by the above-mentioned general formula and exhibiting a temperature width of a supercooled liquid region which is a temperature width between a glass transition temperature (Tg) and a crystallization temperature (Tx) and further contains hydrogen incorporated therein, it remarkably exhibits the following features and effects besides such excellent characteristic as high hardness, high strength, high heat resistance, and high corrosion resistance,
- greatly improved strength, thereby bringing about the long-term reliability as a material, and
- improved vibration-damping properties, as a result, even if vibration is added thereto, the vibration attenuates promptly and the sound simultaneously generated becomes small.
Other objects, features, and advantages of the invention will become apparent from the following description taken together with the drawings, in which:
The amorphous alloy of the present invention uses as a base material the amorphous alloy having the composition represented by the above-mentioned general formula and contains hydrogen incorporated therein. Since the hydrogen present in the metal glass has a small atomic radius (0.3 Å; oxygen and nitrogen: 0.74 Å) as compared with other metal atoms, it can move in the metal glass. As a result, it will bring about such an effect that when a crack caused by a fatigue fracture propagates, hydrogen concentrates in a tip portion of the fatigue crack and this portion hardens, thereby stopping propagation of the fatigue fracture.
A method of incorporating hydrogen into the metal glass may be suitably performed by adding hydrogen gas in an inactive atmosphere to be used in the preparation of a matrix alloy (preform) from a raw molten metal.
Since Zr and Hf which are the main raw materials of metal glass tend to be easily oxidized, raw materials should be melted in an inactive atmosphere. In accordance with the present invention, by using an inactive atmosphere (inert gas) containing hydrogen gas mixed therein when this preform is prepared, it is possible to uniformly mix hydrogen into a preform and eventually to manufacture a metal glass article containing a few amount of hydrogen. Since the hydrogen-containing metal glass produced by this method exhibits considerably improved fatigue strength and vibration-damping properties, it is possible to provide an amorphous alloy material which is reliable as a material to be put in practical use.
The unduly low content of hydrogen in the metal glass is not desirable because hydrogen can concentrate in a tip portion of a crack caused by a fatigue fracture only with difficulty due to its unduly low content and this portion will not easily harden and, as a result, it will be hardly possible to stop propagation of the fatigue fracture. Conversely, if the hydrogen content is too high, since the proportion of bonding between Zr or Hf and a hydrogen atom will increase, the hydrogenated Zr or Hf will be produced consequently, which will result in an undesirable effect of making the material brittle. Generally, the content of hydrogen in metal glass is properly in the approximate range of 0.005% to 10% in a weight ratio, though it depends on the alloy composition.
Although the content of hydrogen in the metal glass is mainly controlled by adjusting the amount of hydrogen gas in the inert gas at the time of production of a matrix alloy, it is also arbitrarily controllable by adjusting other conditions, such as a melting period and a melting temperature. Further, it is preferable that the content of oxygen in the metal glass be 1% or less in a weight ratio during the manufacturing process. If the oxygen content is unduly high so as to exceed 1%, the oxides contained in the metal glass will increase, which will result in an undesirable effect of making the material brittle. Furthermore, another reason is that, if the oxygen content is high, the hydrogen concentrated in the tip portion of the crack during the growth of fatigue fracture and the oxygen contained in the metal glass will cause a reaction and, as a result, the hydrogen which inhibits the propagation of crack will be discharged out of the metal glass as water.
As described above, the alloy which is a base material of the amorphous alloy of the present invention has a composition represented by the general formula: XaMbAlc (wherein X represents at least one element selected from the group consisting of Zr and Hf, M represents at least one element selected from the group consisting of Ni, Nb, Cu, Fe, Co, and Mn, and a, b, and c represent such atomic percentages as respectively satisfy 25≦a≦85, 5≦b≦70, and 0<c≦35) and contains an amorphous phase in a volumetric ratio of 50-100%. Here, the reasons for limiting the atomic percentages a, b, and c of elements X, M and Al to the above-mentioned ranges are that the alloy will become amorphous only with difficulty in the composition outside the above-mentioned range and that the alloy containing at least 50% (volumetric ratio) of amorphous phase will be obtained only with difficulty by an industrial quenching means using a liquid quenching process, for example.
The amorphous alloy of the present invention may be produced by preparing a hydrogen-containing matrix alloy having the above-mentioned composition and rapidly solidifying its molten metal by the liquid quenching process. This liquid quenching process means a method of rapidly cooling the molten alloy. For example, the amorphous alloy may be produced by the following methods.
(1) Roll Process or Twin-Roll Method
In these techniques the cooling rate of about 104-106 K/sec. is attained. When a thin ribbon is produced by this single roll method or the twin-roll method, the molten metal of the above-mentioned composition containing hydrogen incorporated therein in advance is injected through a nozzle hole onto a roll made of, for example, copper or stainless steel and having a diameter of 30-3,000 mm, which is rotating at a constant rate in the approximate range of 300 to 10,000 r.p.m. By this method, various thin ribbon materials having a width of about 1-300 mm and a thickness of about 5-500 μm can be readily obtained.
(2) In-Rotating-Liquid Spinning Method
When a thin wire material is produced by the in-rotating liquid spinning method, the molten metal of the above-mentioned composition containing hydrogen incorporated therein in advance is injected through a nozzle hole under application of a back pressure of argon gas into a liquid refrigerant layer having a depth of about 10-100 mm and retained by centrifugal force in a drum rotating at a rate of about 50-500 r.p.m. In such a manner, thin wire materials may be readily obtained. In this technique, the angle between the molten metal injected from a nozzle and the liquid refrigerant surface is preferred to be in the approximate range of 60° to 90° and the ratio of relative velocity of the injected molten metal to the liquid refrigerant surface is preferred to be in the range of 0.7 to 0.9.
(3) Die-Casting Method
When a metal glass article is produced by the die-casting process, first a preform (matrix alloy) is prepared in advance in an inactive atmosphere by uniformly melting the raw materials of the above-mentioned metal glass by a melting method such as arc melting, and this preform is subjected to die-casting to obtain a final article of metal glass. At this time, by using the inert gas containing hydrogen gas mixed therein as an inactive atmosphere, it is possible to uniformly mix hydrogen into a preform to prepare a hydrogen-containing preform. Subsequently, by using an apparatus as disclosed in JP 2001-246451,A, for example, a preform is supplied into a sleeve which is disposed so as to be reciprocated toward a spruce of a metal mold provided with a cooling means. The preform in the sleeve is melted by heating, injected into the metal mold by means of a plunger slidably disposed in the above-mentioned sleeve to effect casting, and then cooled in a supercooled region in the metal mold to form the amorphous structure peculiar to metal glass. Incidentally, the metal mold may be cooled or may not be cooled. As the case may be, a molten metal may be properly cooled even if the metal mold is heated, depending on the volume ratio of a cavity size to a die set.
Besides the above methods, a thin film may be produced by (4) a sputtering process. Further, a rapidly solidified powder may be obtained by various atomizing methods such as, for example, (5) a high-pressure gas atomizing process, or a spray process. In the case of the sputtering process, by introducing hydrogen into a melting atmosphere which is used for the preparation of a target material by melting, it is possible to similarly produce the metal glass thin film containing hydrogen incorporated therein. In the atomizing process, by using hydrogen-containing gas as the gas to be sprayed, it is possible to make a metal glass powder containing hydrogen incorporated therein.
Whether the rapidly solidified alloy thus obtained is amorphous or not can be known by checking the presence of the halo pattern peculiar to an amorphous structure by an ordinary X-ray diffraction method. Further, the amorphous structure is transformed into a crystalline structure by heating to or above a specific temperature (this temperature is called “crystallization temperature”).
Then, one example of the apparatus for the production of a metal glass article by the die-casting process of the above-mentioned processes will be described hereinbelow with reference to the appended drawings.
Moreover, a plurality of ejector pins 16 (although a pair of ejector pins are used in the embodiment shown in the drawings, they may be three or more according to the number of cavities) are inserted into the metal mold 1 so that they can thrust into the cavities 5 of the metal mold. A connecting rod 17 of these ejector pins 16 is inserted through the holes in the movable platen 11 and the fixing member 13 and constituted so that the lower end face of each ejector pin 16 may be in agreement with the top face of the corresponding metal mold cavity 5 by means of an upwardly urging means and a stopper means (not shown). Incidentally, if the movable platen 11 is elevated to a top dead center after completion of the injection-molding, the upper end face of the connecting rod 17 abuts on the lower end face of a cylinder rod 19 of an ejector cylinder 18 which is attached to the stationary platen 10 so as to align with the connecting rod 17. By actuating the ejector cylinder 18, the cylinder rod 19 depresses the connecting rod 17 and the ejector pins 16 thrust into the cavities 5 respectively.
Further, a cylindrical vacuum housing 20 is fixedly secured to the underside of the movable platen 11 through the medium of a sealing member 8 so as to be suspended therefrom to surround the movable upper mold 3. On the other hand, a sealing frame 21 is fixedly secured to the upper surface of the main platen 7 at the position corresponding to the cylindrical vacuum housing similarly through the medium of a sealing member 8. When the clamping of the movable upper mold 3 to the stationary lower mold 2 is performed by moving the movable platen 11 downward, the outside surface of the vacuum housing 20 may slide on the inner surface of the sealing frame 21 through the medium of a sealing member 8 to form a sealed injection-molding section space “X”.
To a predetermined position of the main platen 7, a molded article extraction cylinder 22 equipped with arm parts 23 which can access to and retreat from the injection-molding section at a predetermined height is attached.
On the other hand, a vacuum chamber 24 for hermetically forming a heat-melting section space “Y” is arranged under the main platen 7 and supported by a frame 48. The shut-off and intercommunication between the injection-molding section space “X” mentioned above and the heat-melting section space “Y” of the vacuum chamber 24 are performed by the closing and opening of the opening 6 by means of a shutter 26 which is actuated by a shutter cylinder 25 so as to move forward and rearward while sliding on the underside surface of the main platen 7.
In the vacuum chamber 24, a cylindrical injection sleeve 27 is disposed just under the position which is in alignment with the sprue 4 of the stationary lower mold 2 and the opening 6 of the main platen 7. The cylindrical injection sleeve 27 is provided with an injection plunger 28 which is slidably disposed therein. The injection plunger 28 is actuated by an injection cylinder 29 which is attached to the lower part of the vacuum chamber 24. Further, the lower end part of the injection sleeve 27 is fixedly secured to a sleeve holding member 30. This sleeve holding member 30 is actuated by a sleeve-moving cylinder 31 and vertically reciprocated while being guided with a sleeve movement guide pin 32. Accordingly, by actuating the sleeve-moving cylinder 31 to effect vertical reciprocation of the sleeve-holding member 30, the injection sleeve 27 is elevated toward the sprue 4 of the metal mold 1 and lowered to the starting position.
Further, a high-frequency induction heating coil 34 as a heating means is arranged around the upper part of the injection sleeve 27. The heating means is not restricted to the high-frequency induction heating and, of course, any known means such as one resorting to the phenomenon of resistance heating may be adopted.
Furthermore, in the vacuum chamber 24 a matrix alloy feeder 35 is disposed in alignment with a side opening 33 of the above-mentioned injection sleeve 27. This matrix alloy feeder 35 comprises a matrix alloy feed tubular body 36 installed in the height location connectable to the side opening 33 of the above-mentioned injection sleeve 27, a matrix alloy cassette 37 disposed on this matrix alloy feed tubular body 36, a matrix alloy supply plunger 38 slidably disposed in the matrix alloy feed tubular body 36 mentioned above, and a matrix alloy feed cylinder 39 which actuates the matrix alloy supply plunger mentioned above. The matrix alloy feed cylinder 39 and the matrix alloy supply plunger 38 actuated by it function as the forcibly transferring means to move the matrix alloy ingot “A” which has dropped into the matrix alloy feed tubular body 36 from the matrix alloy cassette 37 into the injection sleeve 27.
The matrix alloy cassette 37 comprises a turntable 41 rotatably disposed on a mount 40 which is fixedly secured to the matrix alloy feed tubular body 36 and a plurality (although four in the case of the embodiment shown in the drawings, two or three or five or more may be used) of vertical-type cylindrical matrix alloy-accommodating magazines 42 disposed on this turntable 41, as shown in
While the matrix alloy ingot “A” of the bottom which has dropped into the matrix alloy feed tubular body 36 is supplied into the injection sleeve 27 by means of the matrix alloy supply plunger 38, the matrix alloy ingots “A” accommodated in the matrix alloy-accommodating magazine 42 in the piled state do not drop into the matrix alloy feed tubular body 36 because the opening 45 of the mount 40 is closed by the matrix alloy supply plunger 38. However, when the matrix alloy supply plunger 38 retreats to open the opening 45 of the mount 40, the next ingot of the bottom will drop into the matrix alloy feed tubular body 36 and will be served for the next supply. In this way, the matrix alloy ingots “A” in the matrix alloy-accommodating magazine 42 will drop and supplied to the injection sleeve 27 one by one with a predetermined time interval. When the matrix alloy-accommodating magazine 42 becomes empty, the turntable 41 will rotate only a predetermined angle and the following matrix alloy-accommodating magazine 42 will be arranged in the supply position.
The above-mentioned matrix alloy feeder 35 is attached to a slide type lid 46 of the vacuum chamber 24. This lid 46 is slidably laid on guide rails 47 so that the whole matrix alloy feeder 35 can pull out by pulling the lid 46. Accordingly, after completion of the injection molding using the matrix alloy ingots “A” in all the matrix alloy-accommodating magazines 42, a large number of matrix alloy ingots “A” can be ready for supply by one operation which comprises opening a chamber air valve 53 connected to the vacuum chamber 24 to cancel the vacuum condition (the evacuation system L2 of the vacuum chamber 24 is shut off at this time), pulling out the lid 46, and exchanging the matrix alloy cassette 37 for a new one. Incidentally, if the lid 46 is set to the vacuum chamber 24, the leading end face of the matrix alloy feed tubular body 36 will abut on the peripheral part of the side opening 33 of the injection sleeve 27, and the sealing between the lid 46 and the vacuum chamber 24 will be effected by a sealing member 8.
Alternatively, the matrix alloy feeder may be constructed such that the matrix alloys accommodated in the matrix alloy-accommodating magazine are moved upward by a vertically reciprocating pin, for example, and the matrix alloy now in the top position is transferred to the position just over the sleeve by a transferring means such as an arm and charging the matrix alloy into the sleeve from above.
One line L1 (metal mold evacuation line) of the vacuum evacuation system L of a vacuum pump 50 (comprising a diffusion pump and a rotary pump) is connected to the metal mold exhaust holes 15 formed in the movable platen 11 and the fixing member 13 so that the evacuation is continued until the inside of the injection-molding section space “X” reaches a predetermined degree of vacuum. Other line L2 is connected to the vacuum chamber 24 so that the evacuation is continued until the inside of the heat-melting section space “Y” reaches a predetermined degree of vacuum. A metal mold air valve 54 for canceling the vacuum condition of the injection-molding section space “X” and also a vacuum reserve tank 51 are connected to the metal mold exhaust line L1 so that the injection-molding section space “X” can be changed to a vacuum condition instantaneously after the clamping of the movable upper mold 3 to the stationary lower mold 2.
Further, an inert gas container 52 is also connected to the vacuum chamber 24 so that the heat melting of the matrix alloy can be performed under an inert gas atmosphere, such as Ar, depending on the kind of matrix alloy to be used. Reference numerals 55-59 are solenoid valves.
Next, the injection-molding process using the apparatus mentioned above will be described.
<Matrix Alloy Supply Process>
First, After pulling out the lid 46 and setting the matrix alloy cassette 37 in the matrix alloy feeder 35 as described above, the lid 46 is shut. When the chamber air valve 53 is closed, the solenoid valve 58 is opened to effect vacuum suction of the heat-melting section space “Y” of the vacuum chamber 24. At this time, the shielding shutter 26 is closed and the matrix alloy feed section and the heat-melting section are incorporated in the one vacuum chamber 24.
When one of the matrix alloy-accommodating magazines 42 of the matrix alloy cassette 37 is set on a predetermined position, the matrix alloy feed cylinder 39 is actuated so that the matrix alloy ingot “A” which has dropped into the matrix alloy feed tubular body 36 from the matrix alloy-accommodating magazine 42 is pushed into the injection sleeve 27 by means of the matrix alloy supply plunger 38, as shown in
<Heat-Melting Process>
Next, the injection cylinder 29 is actuated so that the injection plunger 28 pushes up the matrix alloy ingot “A” to a melting zone, as shown in
<Injection-Molding Process>
After the molten metal in the injection sleeve 27 has reached a predetermined temperature (the measurement of its temperature may be performed by any suitable method such as, for example, a method of disposing a thermocouple in the injection plunger 28 or a method of using a radiation thermometer as in the case of the example described hereinafter), the high-frequency induction heating coil 34 is demagnetized and the shutter cylinder 25 is actuated to open the shielding shutter 26, thereby intercommunicating the injection-molding section space “X” and the heat-melting section space “Y”. At this stage, the sleeve-moving cylinder 31 and the injection cylinder 29 are promptly actuated synchronously to effect elevation of the injection sleeve 27 and the injection plunger 28, the upper end of the injection sleeve 27 closely contacts the peripheral part of the sprue 4 of the metal mold 1, as shown in
<Molded Article Extraction Process>
After completion of the injection-molding, as shown in
<Shot Cycle>
After extraction of the molded article, the mold-clamping cylinders 12 are actuated again to close the metal mold 1. Subsequently, the metal mold air valve 54 is closed and the solenoid valve 55 is opened. After the injection-molding section space “X” is connected with the vacuum reserve tank 51 and preliminarily evacuated, the solenoid valve 56 is closed, and thus the injection-molding section space is connected with a vacuum pump 50 (the solenoid valve 57 is usually in an opened state). Therefore, the vacuum condition of the injection-molding section space “X” is established for a very short period of time, and the apparatus returns to the condition shown in
On the other hand, in the matrix alloy feeder 35, since the next matrix alloy ingot “A” which has dropped into the matrix alloy feed tubular body 36 from the matrix alloy-accommodating magazine 42 when the matrix alloy supply plunger 38 has been retreated is pushed out of the tubular body by the matrix alloy supply plunger 38 and is supplied into the injection sleeve 27, it is subjected to the following shot cycle.
In the manner as described above, the shot cycle is repeated automatically and continuously until all the matrix alloy ingots “A” accommodated in respective matrix alloy-accommodating magazines 42 of the matrix alloy cassette 37 are used up. After the matrix alloy ingots “A” of the matrix alloy cassette 37 have been completely used up, the solenoid valve 58 is closed and the chamber air valve 53 is opened, and then the lid 46 is pulled out and the matrix alloy cassette 37 is exchanged for a new one, as described hereinbefore. After the exchange of cassette has been completed, the lid 46 is shut and the shot cycle as described above is repeated again.
EXAMPLEPreforms (matrix alloys) were prepared by homogeneously melting the metal glass raw materials (Zr, Al, Cu, etc.) by an arc melting process so as to have the respective compositions shown in the Table. In the preparation of these preforms, an inert gas containing 3 vol. % of hydrogen gas was used to uniformly incorporate hydrogen into the preforms. For the comparison, the preforms containing no hydrogen were also prepared by using an inert gas containing no hydrogen gas.
By using each preform obtained as described above, a test piece of metal glass was prepared by casting it with the apparatus as shown in
Each test piece of metal glass obtained as described above was subjected to the fatigue test. The results are shown in the Table and
The fatigue test was performed by using an Ono type rotating bending fatigue tester using sign wave repeated stress under the condition of the stress ratio R=−1. Cycle frequency was 13 Hz and the fatigue test was performed in the air at room temperature. As a test piece, a rod-like test piece (the sandglass type having a diameter of 16 mm and a constricted central portion, shoulder radius (curvature radius of a constriction transition part) R=16 mm, diameter of the portion to be held in the chuck part of the tester (diameter of the constricted part) φ=8 mm, the shortest diameter of the portion to be fractured, φ=4 mm, and gauge length L=20 mm) was used. Accordingly, the result means a fatigue test result of a smooth material (without notch).
As being clear from the results shown in the Table and
While certain specific embodiments and working examples have been disclosed herein, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The described embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are, therefore, intended to be embraced therein.
Claims
1. An amorphous alloy having a composition represented by the following general formula and containing an amorphous phase in a volumetric ratio of 50-100%, the improvement which comprises hydrogen incorporated therein: XaMbAlc wherein X represents at least one element selected from the group consisting of Zr and Hf, M represents at least one element selected from the group consisting of Ni, Nb, Cu, Fe, Co, and Mn, and a, b, and c represent such atomic percentages as respectively satisfy 25≦a≦85, 5≦b≦70, and 0<c≦35.
2. The amorphous alloy according to claim 1, wherein said hydrogen is present in said amorphous alloy in an amount of 0.005-10% of said amorphous alloy in a weight ratio.
Type: Application
Filed: Jun 9, 2005
Publication Date: Apr 20, 2006
Inventor: Yoshihiko Yokoyama (Himeji-shi)
Application Number: 11/148,655
International Classification: C22C 45/00 (20060101);
