JPS6187839A - Shape memory alloy - Google Patents

Abstract

PURPOSE:To obtain a shape memory Ti-Ni alloy having superior workability, a high transformation temp. and a long repetition life by adding specified amounts of Ni and Cu to Ti, substituting B for part of the Ti, and heat treating the resulting alloy at a specified temp. CONSTITUTION:A Ti-Ni-Cu-B alloy having a composition consisting of 48-50atom% Ni+Cu (Cu<10atom%) and the balance Ti and further contg. B substituted for 0.1-5atom% of the Ti is refined by high frequency vacuum melting. An ingot of the alloy is homogenized at 900 deg.C for 2hr and hot rolled to 9.5mmphi. It is process-annealed, cold rolled to 2.0mmphi, and cold rolled again to 1.6mmphi without carrying out annealing. The resulting rough wire is heat treated at >=700 deg.C to obtain a shape memory alloy having superior hot workability, a high transformation temp. and a long repetition life. The alloy is suitable for use as a material for an actuater working at high temp. such as a steam pressure regulating valve.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a shape memory alloy consisting of r Nr + T+ + Cu and B.

[Prior art]

T1Ni alloy is a reverse-transformation Fe of thermal externalization type martensitic transformation.
It has been revealed that a TiN1-X alloy substituted with a Cu #Co, V, Cr, etc.) also exhibits a similar effect ("Metal J February 13, 1966 issue PP4").
4-48゜Tohoku University Senken Awaho, 28 (1972) 209
~219. Japanese Patent Publication No. 47-2102. Japanese Patent Publication No. 53-285
18° Japanese Patent Publication No. 53-149732).

It is known that the transformation temperature of T1Ni alloy increases as the N1 concentration decreases. However, when the Ni concentration decreases in terms of the stoichiometric amount and the 1τL value, the second phase of Ti2Ni precipitates and makes the alloy brittle, resulting in poor workability.

In addition, 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
℃) is known.

However, according to this heat treatment, homogenization heat treatment (700 ~
The transformation temperature obtained at 1000°C) shows a reverse transformation start temperature (hereinafter referred to as the As point) of +100 to -196°C (depending on the Ni concentration), whereas it converges in the range of +30 to +60°C. As a result, it has become difficult to obtain an alloy that exhibits an As point of +60°C or higher.

For TiNi-X alloys, most of the added elements tend to lower the transformation temperature of the alloy, but Cu, C
o shows no significant dependence on transformation temperature, and Si
.

It is clear that B and Be increase the transformation temperature.

In order to obtain a highly transformed functional alloy (As point of 60°C or higher),
A method of adding one or more kinds of S+ r B and Be + a method of reducing the Nr 17N+ degree can be considered, but both of these methods deteriorate workability (cold workability and machinability such as coiling). In addition, according to the above-mentioned medium temperature heat treatment, the As point is currently 60°C or lower. [Object of the Invention] The present invention aims to provide a high transformation temperature (As of 60°C or higher) with good workability and repeated repetition. The purpose of the present invention is to provide a T1Ni-based shape memory alloy with a long life.

[Structure of the invention]

In the present invention, the total content of Ni and Cu is 48 to 50 at%.

In an alloy where the balance is Ti, a part of Ni is replaced with B by 0.1
It is a shape memory alloy with ~5 at% substitution.

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

Ti100-xNix-(y+z)CuyBzHowever,
48≦X≦50 0<y≦10 0.1≦2≦5 [Effects of the Invention] The TiN1CuBe alloy of the present invention exhibits a good shape memory effect similar to that of the T1Ni alloy, and is also highly workable.

As shown in Tables 1 and 2, it has the advantage of exhibiting a high transformation function.

The present invention will be explained below based on Examples.

〔Example〕

The TiN1CuB composite obtained by high frequency vacuum melting was homogenized at 900°C for 2 hours, then hot...
It was processed to a diameter of φ9.5 using hot rolls. After that 700～
Intermediate annealing was performed at 800° C. and cold working was performed to φ2.0, followed by cold working to φ1.6 without annealing.

Part of the obtained wire was subjected to a homogenization treatment at 750°C,
A portion was subjected to medium temperature treatment at 700° C. for 30 minutes.

The results are shown in Table 11 and Table 2.

Regarding T1Ni alloy, its workability tends to deteriorate as it deviates from the stoichiometric value.

TI 52N+ 48 could not be hot worked (hot working conditions = 850°C).

On the other hand, this alloy shows a tendency for workability to worsen when B addition exceeds 3 at%, but much better results were obtained than with conventional T1Ni alloys.

In the scope of the claims of the present invention, the addition of B is within 5 at%.
This is because if it is more than at%, the workability will be significantly deteriorated and there will be problems with cold workability, so the optimum content is 3 at% or less. Further, if the amount is less than 0.1 at%, the effect of addition is hardly noticeable.

Regarding the amount of CU added, up to +10 at% does not cause significant deterioration in workability or decrease in transformation temperature;
If it exceeds 10 at%, there will be a noticeable deterioration in workability and it will be difficult to obtain the desired high transformation material.

Table 2 shows the results of investigating changes in transformation temperature due to repeated heating and cooling thermal cycles for materials heat-treated at 700°C for 30 minutes.

A significant change in transformation temperature is observed for the T51''49 alloy, but no significant change is observed for the claimed alloy.

In this way, the alloy of the present invention made it possible to provide a shape memory alloy that is resistant to cycling at temperatures above 60°C. This can be applied to actuators that operate at high temperatures, such as steam pressure regulating valves.

Remaining days table below-1 ◆ 750℃X1hrfi treatment ・) Workability...
Good O〃 ・・Fair △ 〃 ・・Difficult

Claims (2)

[Claims] (1) Ni and Cu total 48 to 50 at% (Cu:1
0 at% or less), and a TiNi-Cu alloy consisting of residual Ti, in which Ni is replaced with B at 0.1 to 5 at%. (2) The shape memory alloy according to claim 1, which maintains thermal cycle life characteristics even when heat treated at a temperature of 700°C or higher.