JPH0686639B2 - Shape memory alloy - Google Patents

Description

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

[Conventional technology]

It is known that TiNi alloy exhibits a remarkable shape memory effect accompanying the reverse transformation of thermoelastic martensitic transformation. In addition, a part of Ni may be replaced with another element X (eg Fe, Cu, Co, V, Cr, etc.)
It is known that the TiNi-X alloy substituted with is similar in effect. ("Metal" February 13, 1966, pp44-48, Tohoku University Research Bulletin 28 (1972) 209-219, JP-A-47-2102,
See JP-A-53-28518 and JP-A-53-149732. ) Unlike other TiNi-X alloys, the TiNi-Cu alloy has a close martensitic transformation start temperature (hereinafter abbreviated as M _s point) and a reverse transformation start temperature (A _s point) as the Cu content increases. However, it has the feature that it will eventually reverse.

For _{example, Ti 50 Ni 50-x Cu} x In x = 10 in the alloy M _s point and A _s
The points are reversed and the M _s point becomes higher than the A _s point.

[Problems to be solved by the invention]

The feature of using a TiNi-Cu alloy as a shape memory element is that the hysteresis can be reduced because the M _s point and the A _s point are close to each other or reversed. (The hysteresis of TiNi alloy is 20
-30 ℃, 5-10 ℃ for TiNiCu alloy) It is generally known that the transformation temperature of TiNi alloy rises as the Ni concentration decreases. However, if the Ni concentration is reduced below the stoichiometric value, the second phase of Ti ₂ Ni precipitates and the alloy becomes brittle, resulting in poor workability.

This tendency is remarkable also in TiNi-Cu alloy. Also Cu
The workability deteriorates as it becomes brittle with the added amount.
If it exceeds at%, it cannot be processed.

INDUSTRIAL APPLICABILITY The present invention has excellent workability and has a small hysteresis.
An object is to provide a system shape memory alloy.

[Means for solving problems]

According to the present invention, Ni and Cu total 48 to 50 at% (provided that Cu
In the TiNi-Cu alloy consisting of the balance Ti and at least 3 at% but not more than 10 at%), Ni is replaced by Ru by 0.25 to 3 at% to obtain a shape memory alloy.

The composition of the shape memory alloy according to the present invention can be shown by a formula as follows.

Ti _100-x Ni _{x- (y + z)} Cu _y Ru _z However, 48 ≦ x ≦ 50 3 ≦ y ≦ 10 0.25 ≦ z ≦ 3 [Effect of the invention] The TiNiCu-Ru alloy of the present invention is the same as the TiNiCu alloy. In addition to exhibiting a shape memory effect with a small hysteresis, a working rate of 40% or more is possible in cold working, which has the advantages of rich workability and high transformation function.

〔Example〕

 Examples of the present invention will be described below.

Each TiNiCuRu alloy having the composition shown in Table-1 and obtained by high-frequency vacuum melting was processed to a diameter of 9.5 with a hot hammer and hot roll after homogenizing treatment at 900 ° C for 2 hours. After that 700 ℃
Intermediate annealing was performed at 0, and cold working was performed to φ1.0 to obtain a functional evaluation wire and at the same time the workability was investigated. For the hot workability, the forging ratio was measured and 1.2 for TiNi alloy was normal, and for the cold workability, a workability of 40% was normal.

The obtained wire was heat-treated at 750 ° C for 0.5 hr. The results of cold workability and transformation temperature obtained by these
Shown in 1.

The TiNi-Cu alloy gradually deteriorates in workability up to a Cu addition amount of 10 at%, and is markedly deteriorated if the Cu addition amount exceeds 10 at%.

On the other hand, this alloy showed cold workability similar to that of the Ti ₅₀ Ni ₅₀ alloy, and obtained much better results than the conventional TiNiCu alloy.

In the claims of the present invention, the addition amount of Cu is set to 10 at% or less.
This is because the effect of the addition of more than at% was not recognized so much with respect to hysteresis and only deteriorated the workability.

The Ru addition amount is set to 3 at% or less because the effect of the addition on the characteristics (M _s point, hysteresis) is not observed any more than 3 at% and the optimum value is 0.5 to 1 at. %. Also, if it is less than 0.25 at%, the effect of the addition is hardly noticeable.

Thus, in the alloy according to the present invention, Ni is 0.25 to 3 at% in Ru.
By substituting, the three conditions of high workability and hysteresis of 15 ° C or less are realized at the same time without lowering the high martensitic transformation start temperature, which is a characteristic of conventional TiNiCu alloys.

Next, embodiments of the present invention will be listed below.

(1) The shape memory alloy according to claim 1, which is capable of obtaining a martensite transformation start temperature of 50 ° C. or higher and a hysteresis (difference between the martensite transformation start temperature and the reverse transformation completion temperature) of 15 ° C. or lower.

(2) Hot work is easy and intermediate annealing (strain relief annealing)
In the post-cold working, a working rate of 40% or more is possible (1)
Shape memory alloy according to.

Claims (1)

[Claims] 1. A total of 48 to 50 at% of Ni and Cu (provided that Cu is 3a
A shape memory alloy, characterized in that, in a TiNi-Cu alloy consisting of at least t% but not more than 10 at%) and the balance of Ti, Ni is replaced by 0.25 to 3 at% with Ru.