JP2680832B2 - Method for producing Cu-Zn-Al sintered superelastic alloy - Google Patents

Description

The present invention relates to a method for producing a Cu-Zn-Al sintered superelastic alloy which is inexpensive and can be produced by a simple process of forming-sintering. is there.

[Conventional technology]

Usually, a metallic material undergoes plastic deformation when a stress above the elastic limit is applied, and residual strain remains even after unloading.

However, shape memory alloys recover their original shape when heated above the critical temperature. Moreover, in the case of this shape memory alloy, due to the property called pseudoelasticity, the shape returns to its original shape even if a large strain of 5% or more is applied in the temperature range above the Af point,
There is a so-called superelastic phenomenon in which residual strain does not remain. This phenomenon is due to the stress-induced martensitic transformation above the Af point and its inverse transformation.

Ti has been practically used in shape memory alloys.
Both the -Ni alloy and the Cu-Zn-Al alloy were manufactured by the melting method. Among them, Ti-Ni alloy is Cu-Zn-
Reciprocating stress, fatigue strength and other mechanical properties are remarkably superior to Al alloys, and by utilizing the large superelastic function of 5% or more, the so-called Ti-Ni superelastic wire is already used to name the eyeglass frame. In addition, it has been put to practical use as a biofunctional material for bone grafting or orthodontics. However, since Ti-Ni alloys are expensive and difficult to work, they have not been widely used except in special cases.

On the other hand, as a Cu-based shape memory alloy, Cu-Zn produced by the melting method
-Al alloys have been put to practical use. However this Cu
-Zn-Al alloy is cheaper than Ti-Ni alloy,
Generally, coarsening of crystal grains is likely to occur in the solution treatment process, which causes a grain boundary fracture due to stress concentration, and therefore has low mechanical properties and a small superelasticity of 5% or less. Application to the same field as Ti-Ni alloy is not considered.

[Problems to be solved by the invention]

The present inventors, when variously examining the Cu-Zn-Al alloy to develop a superelastic function, this superelastic function can be surely imparted by going through a specific manufacturing process by powder metallurgy. And completed the present invention.

[Means for solving the problem]

The present invention includes (1) Zn25 to 28 wt%, Al4 to 4.2 wt%, balance C
Cu-Zn-Al sintered superelastic alloy having composition of u and (2) Cu-Zn alloy powder of -280 mesh containing Zn in an amount of 30 to 50 wt% and the balance being Cu, and Al in an amount of 30 to 50 wt% and the balance Cu is -280 mesh Cu-Al alloy powder, and -250 mesh Cu
Powder and blended in a predetermined proportion, 0.05 to 1 wt% of a fluoride as a sintering aid is mixed therein, and the green compact obtained by molding the obtained mixed powder is sintered at 850 to 950 ° C, and then, The obtained sintered member was heated to 500 to 850 ° C. and then rapidly cooled at a cooling rate of 10 ³ ° C./s or more, and then tensile stress was applied to the sintered member within a range in which a residual strain of 1 to 3% was generated, and 500 after heating to to 850 ° C., a Cu-Zn-Al sintering method for manufacturing a superelastic alloy, characterized in that quenching at 10 ³ ° C. / s or more cooling rate.

[Action]

-280 mesh Cu with 30 to 50 wt% Zn and balance Cu
-Zn alloy powder and Al 30 to 50 wt% and the balance Cu-280
The main material is a mixture of mesh Cu-Al alloy powder and -250 mesh Cu powder in a predetermined ratio. Among these, Cu-
The Zn alloy powder and the Cu-Al alloy powder serve as a master alloy powder for allowing the Zn and Al components to be diffused uniformly during sintering and to be uniformly diffused. Therefore, in the case of Cu-Zn alloy powder, Zn
Is less than 30%, the necessary amount of Zn is added, so that the mixing amount becomes large and the mixing amount of the Cu-Al alloy powder becomes relatively small. This means that the distribution of Al in the mixed powder becomes coarse and, as a result, the diffusion of Al becomes slow. In such a case, the desired superelastic function is not exhibited, which is not preferable. Conversely, Zn is 50%
Above, the phenomenon of Zn removal during sintering is extremely unfavorable.

In the case of Cu-Al alloy powder, if the Al content is 30% or less, the mixing amount becomes large in order to add the required amount of Al, as in the case of the Cu-Zn alloy powder, and the mixing amount of the Cu-Zn alloy powder is relatively large. Is less.
This is not preferable because the distribution of Zn in the mixed powder becomes rough and, as a result, the diffusion of Zn is slowed down, and in such a case, the desired superelastic function is not exhibited. Conversely, Al is 50%
In the above case, the melting point of the Cu-Al alloy powder becomes 600 ° C. or less, the Cu-Al alloy powder melts early at the time of sintering, relatively coarse residual pores are formed, and the superelastic function is not uniformly exhibited, which is not preferable. In the present invention, the main raw material Cu powder, Cu-Zn alloy powder and Cu-
As for the Al alloy powder, powder with a particle size of -250 mesh or smaller is used, especially Cu-Zn alloy powder and Cu-Al.
As the alloy powder, -280 mesh fine powder is used. Thus, a superelastic alloy was obtained by using powder of -250 mesh or smaller. Although the cause is not clear, the crystal grains of the melting material are usually 100 to 400 μm, and it is necessary that the crystal grains be at least 100 μm or less in view of the fact that the melting material does not have a superelastic function.
Further, in the present invention, regarding the Cu-Zn alloy powder and the Cu-Al alloy powder, when the powder of +280 mesh is included, the distribution of Al and Zn in the mixed powder becomes rough, and in such a case, the purpose and It is not preferable because it does not exhibit the superelastic function.
Further, the present inventors, when completing the present invention, studied Cu-Zn-Al alloy powder by the water atomizing method, but the compressibility is poor, the density ratio after sintering is 90% or less,
It was confirmed that it became a porous sintered member and no superelastic function was exhibited. Regarding this, in the case of Cu-Zn-Al alloy powder by the water atomizing method, it is very hard because it has a crystal structure having a fine quenching composition of several μm, and as a result, in a normal die molding method, Since a high-density green compact cannot be molded, it is presumed that a high-density sintered body cannot be obtained, and therefore superelasticity does not develop. Next, in the production method of the present invention, fluoride was added to the raw material powder as a sintering aid in an amount of 0.05
Need to mix ~ 1wt%. This fluoride has the effect of decomposing the Al ₂ O ₃ coating formed on the particle surface and promoting sintering. Fluoride used for this includes AlF ₃ , NaF, KF, etc.,
It shows almost the same effect. If this fluoride content is 0.05% or less, it does not have such a function and a dense sintered body cannot be obtained, so that the superelastic function cannot be exhibited. On the other hand, even if 1% or more of this fluoride is added, the above-mentioned improvement effect is not improved, but conversely, the corrosion of the alloy itself is caused, or the fluoride component that volatilizes in the sintering atmosphere increases, so that It is not preferable because it corrodes the inner wall and damages the sintering equipment. Next, the formed green compact is sintered at 850 to 950 ° C in a reducing atmosphere. Sintering at 850 ° C. or lower is not preferable because the diffusion of Zn and Al is insufficient, segregation occurs in the structure, and a uniform superelastic function cannot be obtained, and as a result, the superelastic function of the entire alloy cannot be exhibited.

If sintering is performed at 950 ° C. or higher, the Zn removal phenomenon becomes active, a predetermined amount of Zn cannot be maintained by volatilization of Zn, and the superelastic function is not exhibited, which is not preferable. Then, the obtained sintered member is heated to 500 to 850 ° C. and then rapidly cooled at a cooling rate of 10 ³ ° C./s or more, so-called solution treatment is performed. The heat treatment in this solution treatment must be performed at 500 to 850 ° C. At 500 ° C., uniform solution treatment cannot be performed, and at 850 ° C. or higher, the crystal grains become coarse, which is not preferable. Further, the rapid cooling after the heat treatment in the solution treatment must be performed at a cooling rate of 10 ³ ° C / s or more. If the cooling rate is less than this, uniform solution treatment cannot be performed. For the sintered member that has been subjected to the solution heat treatment as described above, 1
Apply tensile tension to the extent that residual strain of ~ 3% occurs, and reapply 50
After heating to 0 ~ 850 ℃, it is necessary to quench at a cooling rate of 10 ³ ℃ / s or more. By this operation, a superelastic function of 5% or more can be exhibited. First, although it is not theoretically clarified that a tensile stress that gives a residual strain of 1 to 3% is applied, the slip resistance generated in the grain boundaries is released by an operation required only for the sintered member. Therefore, it is presumed that the resistance during the slip deformation is relaxed, and as a result, the stress-induced martensite formation is facilitated. If the residual strain is 1% or less, the releasing effect is small, while if it is 3% or more, grain boundary fracture occurs, which is not preferable. The reason for applying the tensile stress in this step is to uniformly release the slip resistance of each grain boundary, and it is not preferable because stress is not uniformly applied to each grain boundary due to compression or bending stress. The sintered member to which the tensile stress is applied in this way becomes a Cu-Zn-Al sintered superelastic alloy capable of exhibiting a superelastic function by performing solution treatment next. The effect of the solution treatment after the slip resistance cancellation treatment has not been theoretically clarified, but if this operation is not performed, the slip resistance cancellation treatment performed in the previous step may not be performed uniformly. It may occur, and the superelastic function may be insufficient in the entire alloy, which is not preferable. For this reason, the final solution treatment is performed in order to make the entire alloy have a uniform structure, and this solution treatment is performed under the same conditions as the solution treatment after sintering. By repeating the treatment for releasing the sliding resistance of the grain boundary and the subsequent solution treatment, a Cu-Zn-Al sintered superelastic alloy having high elongation can be obtained.

〔Example〕

The electrolytic Cu powder of -250 mesh shown in Table 1, Cu-Zn alloy powder of -280 mesh Zn35% by the water atomization method and the balance Cu, and -280 mesh Al4 of the grinding method
A Cu-Al alloy powder containing 8% and the balance Cu was blended in a ratio shown in Table 2, and 0.1 W of fluoride AlF ₃ was added to this main raw material powder.
t% was added and mixed with a V-type mixer for 30 minutes. The resulting mixed powder was molded into a tensile test piece of a sintered body according to the JSPM standard 2-64 at a molding pressure of 7 t / cm ² , and the mixture was heated in a hydrogen atmosphere in a tubular electric furnace.
Sintering was performed at 0 ° C for 60 minutes to obtain a sintered member having a density ratio of 97%. Then, the obtained sintered member was heated in a tubular electric furnace at 80 in Ar atmosphere.
After heating and holding at 0 ° C. for 10 minutes, it was rapidly cooled in ice water at 0 ° C. After this series of solution heat treatments, tensile stress is applied with an Instron tester so as to give a residual strain of 2% after unloading, and finally the solution heat treatment is performed under the same conditions as after sintering. −
A Zn-Al sintered alloy member was obtained. Next, as a functional test, Zn, A
As a result of performing a tensile test on three types of sintered members No. 1, 2, and 3 shown in Table 2 having different composition of l using an Instron tester, from the stress strain curve, No. 1, 2, 3 Super elastic elongation of 5% or more was observed in all three types of
Regarding the alloy having the composition of No. 2 containing 26% Zn and 4.1% Al and the balance being Cu, as shown in FIG. 1, a remarkable superelastic elongation of 7.8% was observed.

[Effects of the Invention] As described above, the present invention has an effect that a superelastic alloy can be easily manufactured by a simple manufacturing process of an inexpensive Cu-Zn-Al sintered superelastic alloy.

The Cu-Zn-Al sintered superelastic alloy produced by the present invention is an industrially useful invention because it can be provided at a low cost for the same use as the Ti-Zi alloy.

[Brief description of the drawings]

FIG. 1 shows the stress-strain curve of the sintered member sample No. 2 of the example of the present invention measured by an Instron tester.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 59-185743 (JP, A) JP 59-31856 (JP, A) JP 59-145744 (JP, A) JP 54- 100908 (JP, A)

Claims (1)

(57) [Claims] 1. A Zn containing 30 to 50 wt% and the balance being Cu -280
Cu-Zn alloy powder for the mesh and 30-50 wt% of Al and the balance
Cu of -280 mesh Cu-Al alloy powder and -250 mesh
Cu powder was mixed in a predetermined ratio, and 0.05 to 1 wt% of a fluoride was mixed as a sintering aid, and a green compact obtained by molding the obtained mixture was sintered at 850 ° C to 950 ° C, and then, The obtained sintered member was heated to 500 to 850 ° C. and then rapidly cooled at a cooling rate of 10 ³ ° C./s or more, and then tensile stress was applied to the sintered member within a range in which a residual strain of 1 to 3% was generated, and 500 After heating to ~ 850 ° C, 10 ³ ° C /
Cu-Zn-A characterized by rapid cooling at a cooling rate of s or more
l Manufacturing method of sintered superelastic alloy.