JPS61153249A - Ti-ni-cu shape memory alloy - Google Patents

Abstract

PURPOSE:To obtain reduced residual stress as well as a transformation temp. as low as <=30 deg.C As point by incorporating Ti, Ni, and Cu in a proportion shown in a prescribed formula and by carrying out heat treatment at prescribed temp. after cold working. CONSTITUTION:The Ti-Ni-Cu shape memory alloy has a composition represented by the formula Ti100-xNix-yCuy [where (x)=51-53 and (y)=5-10] in atom%, and is obtained by heat treatment at 400-600 deg.C after cold working. This alloy provides reduced residual stress as well as the low transformation temp. where prolonged repeatable life longevity can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a shape memory alloy consisting of Ni, Ti and Cu.

[Prior art and its problems]

It is known that T1Ni alloy exhibits a remarkable shape memory effect accompanying the reverse transformation of thermoelastic martensitic transformation. Also, Tl in which part of Ni is replaced with other elements such as Cu
It is widely known that Ni and -XCux alloys also exhibit similar effects. Regarding the transformation temperature of the T1Ni binary alloy, #Ti
In the 49''51 alloy, the I rutinsite transformation initiation temperature (
Hereinafter, it will be abbreviated as Ms point. ) has been shown to be approximately -50℃, and the reverse transformation start temperature (hereinafter referred to as the As7 point) is approximately -30℃ (Tohoku University Ore Processing and Refining Research Institute Report, Soruna Vol. 37, No. 1 (June 1981) p.
p79-88).

Furthermore, for the purpose of improving shape memory properties (improving fatigue properties), the temperature at which recrystallization does not occur after cold working (300 to 500°C) is
) is shown by Buehler (Wire J, Vol 2 + June
1969 pp41-49).

However, even if the above two conventional technologies are combined, the present invention has a low transformation function that operates at temperatures below 30°C.
-Ti-Cu shape memory alloys are difficult to obtain. That is, the Ti4. Ni51
Make an alloy and heat it at 700℃~1000℃40
When heat treatment is performed at a relatively low temperature of about 0℃, 5 Ms' (transformation start temperature associated with R phase transformation), which is related to R phase transformation.
appears, the 9M8' point exceeds approximately 50℃, and the As point exceeds 30℃, making it impossible to provide the desired low transformation function.Moreover, the transformation temperature fluctuates considerably due to repeated thermal cycles, and the As point exceeds 30℃. I learned that it has a short lifespan. Tl further heat-treated at this relatively low temperature 4. N151
For example, if the alloy is used as an actuator that operates reversibly between 30°C and 10°C, score A8 is 2.
If it is possible to set it to 5℃, then 700℃ to 1000℃
After heat treatment, the M8 point is approximately 150 degrees and the A8 point is approximately 120 degrees.
℃, so the residual load is large (approximately 50%) because martensitic transformation does not occur completely at 10℃.
, Even from this point of view, it is difficult to put it into practical use.

[Purpose of the invention]

The present invention has a low transformation temperature (A) with a high repeat life.

The purpose of the present invention is to provide a shape memory alloy that has a small residual load during cortin site transformation (point 30°C or lower) and cortinsite transformation.

[Structure of the invention]

The present invention is a shape memory alloy consisting of a total of 51 to 53 at% of Ni and Cu, with the remainder being Ti.

The composition of the shape memory alloy according to the present invention is expressed as follows.

51≦x53 I゛5 < Jt < 10 After cold working, heat treatment is performed at 400°C to 600°C.

〔Effect of the invention〕

The TiN1Cu alloy of the present invention exhibits a good shape memory effect similar to that of the T1Ni alloy, and at the same time exhibits a low transformation function.
It has the advantage that the residual stress (yield stress) during martensitic transformation is small, and the change in transformation temperature is small even when thermal cycles are applied.

〔Example〕

The present invention will be described in detail below with reference to examples.

Various alloys were obtained by high frequency vacuum melting, respectively, T1Ni binary alloy and TiN1Cu alloy. After heating them at 900° C. for 2 hours, they were processed with a diameter of 9.5 mm using a hot hammer and a hot roll. after that.

φ1,3 while performing intermediate annealing at 700℃~800℃
After that, cold working was performed from φ1.3 to φ1.0 (processing rate was 41 inches). A part of the obtained wire is 7
A homogenization treatment at 50°C was performed, and some were subjected to a medium temperature treatment at 500°C for 30 minutes.

Table 1 shows the above results. As you can see from this table *T
In the iN1Cu alloy, there is no noticeable deterioration in workability when Cu is present up to 10 at%, but when it exceeds *10 at%, it cannot be worked. Furthermore, when Cu was added at p 5 at % or less, a remarkable increase in the A8 point was observed under medium temperature treatment conditions of 500° C., and no effect of Cu addition was observed. Furthermore, Ti is 47 at% or less -1 *750℃XIhr heat treatment ◎Workability...Good I$
500°C There wasn't.

Table 2 shows some of the alloys obtained as described above (Ti49Ni
46Cu5 alloy r T148N145Cu5 alloy) 5
It shows the change in A8 temperature after thermal cycling (thermal cycle conditions, between 10°C and 40°C) after medium temperature treatment at 00°C. For comparison.

TI 49N151 alloy treated at 550℃ and 500℃
Thermal cycle data is also shown for processed samples. As is clear from Table 2, the TiN1Cu alloy shows no significant temperature change with repeated cycles.

Margin Table 2 below: 500°C x 30ml (1'): 550°C x 30ml Next, the above alloy was stretched by 3% in the range of 0°C to 40°C, and the yield stress at each temperature was determined.

FIG. 1 is a diagram showing the dependence of yield stress on temperature of the above alloy. In the figure, (1) is the alloy wire corresponding to A1 in Table 2 that has been heat treated at 500°C x 30m1n.
(3) is the Af alloy wire heat treated at 550°C x 30 m1n, (3) is the alloy wire from Ya 3 heat treated at 500°C x 30 m1n, and (7) is the alloy wire from Ya 7 heat treated at 500°C x 30 m1n.
The product that has been heat-treated for a minimum of 10 minutes is used as a raincoat. As is clear from FIG. 1, there is a clear difference in yield stress in the TiN1Cu alloy from approximately the vicinity of point A8. That is, there is a difference in deformation stress between the martensitic transformation temperature range and the reverse transformation temperature range. This shows that deformation is easy at low temperatures of 0 to 10°C, that is, residual stress is small. On the other hand, Ti4. In the Ni54 alloy, no clear difference in stress is observed near point AB, and the stress changes only approximately linearly. This indicates that the residual stress is large on the low temperature side.

In this way, the alloy of the present invention has an As point of 30°C or lower after 7 cycles.
It was possible to provide a shape memory alloy that is strong against L and has small residual stress.

Note that the optimum alloy composition of the present invention is T1 in view of workability.
is 49-48 at%, (Ni-+:Cu) is 51-48 at%
52 at%, and Cu is 5 to 7 at%.

Such devices that operate around or below room temperature (Z20° C.) can be applied to refrigerators, automobiles, and the like.

[Brief explanation of the drawing]

Figure 1 shows a graph showing the yield stress dependence on temperature for T1Ni and TiN1Cu alloys.

Claims (1)

[Claims] 1. Composition is Ti_1_0_0_ in atomic percent
-_xNi_x_-_yCu_y, where x and y are expressed as 51≦x≦53 5≦y≦10, are heat treated at 400 to 600°C after cold working, and have low transformation. A TiNiCu shape memory alloy that exhibits high performance, low residual stress, and small fluctuations in transformation temperature even when subjected to thermal cycles.