JPH0463139B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a shape memory alloy, specifically a shape memory alloy in which a part or all of Ni in a Ti-Ni alloy having a shape memory effect is replaced with Pd. be.

Conventional technology A Ti-Ni alloy with a composition of 50-50 atomic percent or around it undergoes thermoelastic martensitic transformation, and the deformation imparted to the alloy in the martensitic phase is heated to the matrix region. It exhibits the so-called shape memory effect, where it instantly recovers to its pre-deformed shape. In addition to Ti-Ni alloys, this effect also applies to Cu-Al-Ni, Cu-Zn-
It is found in many alloys such as Al, Fe ₃ -Pt, Au-Cd, Ag-Cd, etc., but from practical aspects such as strength, ductility, and fatigue resistance, Ti-Ni alloy and some Cu
Base alloys are currently attracting attention as having useful properties. In addition, when comparing Ti-Ni alloys and Cu-based alloys, it is found that although Ti-Ni alloys are more expensive, they exhibit good workability and have better fatigue resistance than Cu-based alloys. Because of this, Ti-Ni alloys are used as industrial materials, medical materials,
Shape memory alloys are mainly used in the field of energy conversion materials.

Problems to be Solved by the Invention The maximum shape recovery temperature of Ti-Ni alloy is 390K at most, and currently its application as a shape memory alloy is limited to fields where shape recovery is below this temperature. be. Therefore, it is desired to develop a shape memory alloy having a higher shape recovery temperature for application in various fields.

By the way, the shape recovery temperature of Ti-Ni alloy is (1)
It is affected by Ni concentration, (2) heat treatment, (3) substitution of Ti or Ni by a third element, etc. for example
When annealed at a temperature of 1023K or higher for 2 hours (7.2Ks [kiloseconds]) and water quenched,
When the Ni concentration is 49.6 at% or less, the temperature shows a constant value of 390K, but in the concentration range of 49.6 to 51.0 at%
As the Ni concentration increases, it decreases linearly at a rate of 93.9K per atomic %. In addition, looking at the effects of heat treatment, in Ti-Ni alloys, when the annealing temperature decreases,
On the Ni-excessive side, a two-step transformation of parent phase → intermediate phase → martensitic phase appears, and as a result, the shape recovery temperature is
It increases as the annealing temperature decreases, independent of the Ni concentration. However, as mentioned above, it will never exceed 390K.

On the other hand, looking at the effect on shape recovery temperature when replacing Ti or Ni in Ti-Ni alloy with a third element, we find that
When 3d transition metals (V, Cr, Mn, Fe, Co) are selected as replacement elements, the shape recovery temperature decreases significantly with 1 to 3 at% substitution, and when Ni is replaced with Cu, this temperature almost decreases. The result is that there is no change.

Therefore, the purpose of the present invention is to
In a temperature range higher than the shape recovery temperature of Ni alloy,
The object of the present invention is to provide a new shape memory alloy that exhibits a shape recovery effect to solve the above problems.

Means for Solving the Problems The present invention solves the above problems by using a shape memory alloy containing Ti: 48.5 to 50.4 atomic % and Pd: 15 atomic % or more and less than 50 atomic %, with the balance being Ni. That's what I got.

The present invention will be explained in detail below.

Some of the inventors previously investigated Ti ₅₀ Ni _50-X Pdx (x = 0 to 12) alloys and
At a concentration χ _Pd = 0 to 5 mol%, the transformation temperature decreases rapidly as the Pd concentration increases, and when the Pd concentration χ _Pd = 5 to 12
It was revealed that the transformation temperature showed a slight increase in atomic percent.

The inventors have further determined that the Ti ₅₀ Ni _50-X Pdx alloy is
We conducted a detailed study in the composition range of χ _Pd = 15 to 50 atomic percent, and found that the shape recovery temperature of this alloy increases continuously and linearly with increasing Pd concentration.
Also, by firing in the temperature range of 773-1273K.
It was confirmed that the relationship between Pd concentration and shape recovery temperature is not affected, and that a shape memory effect exists in alloys with these compositions in the composition range of χ _Pd = 15 to 50 atomic %.

Regarding the Ti concentration, when the Ti concentration is around 50 atomic %, when the concentration increases to 50.4 atomic %, the transformation temperature decreases, and when it decreases to 48.5 atomic %, the transformation temperature increases.

The present invention has been achieved based on the above findings.

Next, the present invention will be specifically described with reference to Examples.

Examples Sponge Ti (99.7% purity), electrolytic Ni (99.95% purity), and plate-shaped Pd (99% purity) were used as raw materials for the samples. Each raw material was melted in advance for degassing. The manufacturing procedure is as follows. A Ti ₅₀ pd ₅₀ alloy is made using the raw materials Ti and Pd as one base material, and another using Ti, Ni and Pd.
A Ti-Ni-Pd alloy was made and used as the other base material. These two base materials are cut into small pieces, weighed and blended, and melted in an argon atmosphere arc furnace to form Ti ₅₀ Ni _50-X Pdx.
Alloy (x=15, 17.5, 20, 22.5, 27.5, 30, 35,
40, 45, 50) ingots (approximately 20 g) were made. These were subjected to homogenization heat treatment at 1273K for 4 hours, and then hot rolled at 1173K to a thickness of 1 mm to form each sample.

From these samples, specimens for differential scanning calorimetry (about 2 x 2 x 1 mm) for identifying the transformation temperature and samples (about 10 x 1 x 0.5 mm) for examining the shape memory effect were cut out. The specimens were annealed for 4 hours, water quenched, and subjected to the above test.

After the test, one that had been annealed at 1073K x 4 hours (14.4Ks) and water quenched was selected from all the samples and measured. The transformation temperature of this sample (Ms, Mf,
The relationship between As, Af) and Pd concentration χ _Pd was investigated. This relationship is shown in FIG.

Here, the transformation temperatures Ms and Mf represent the start and end temperatures of transformation in the cooling process, respectively, and As,
Af represents the start and end temperatures of reverse transformation in the heating process, respectively. Note that the shape recovery temperature corresponds to Af.

As shown in the figure, each transformation temperature increases linearly with increasing Pd concentration. In particular, the Af temperature, that is, the shape recovery temperature, is determined by the empirical formula Af/K=91+15.39×(χ _Pd /atomic%), χ _Pd = 15
~50atomic%, 322K (χ _Pd = 15atomic
%) to 861K (χ _Pd = 50atomic%) continuously,
Moreover, they found that it increases linearly.

Also, looking at the influence of annealing temperature on this,
The Af temperature of each sample annealed for 4 hours in the temperature range of 673K to 1273K excluding 1073K and water quenched is:
The specimens were annealed at 1073K for 4 hours as shown in Figure 1, and showed almost the same values as the quenched samples.

Therefore, no influence of annealing temperature on Af temperature is observed.

In the shape memory effect test, qualitative shape recovery was investigated by bending the above sample at room temperature and then heating it above the Af temperature. The results of testing samples annealed at 1073 K for 4 hours and subjected to water quenching showed that all samples with χ _Pd =15 to 50 atomic% exhibited a shape memory effect.

From the above test results, Ti ₅₀ Ni _50-x Pdx (χ=15
~50) It was found that the alloy can be stably used as a shape memory alloy in application fields where the shape recovery temperature is in the temperature range of 322 to 861K, without being affected by heat treatment.

Although the samples used in this example were melted in an arc furnace in an argon atmosphere, there is an industrial method for producing the alloy of the present invention by melting in a vacuum high-frequency induction furnace using a graphite crucible. . This method has been used in the production of conventional Ti--Ni alloys, but has the advantage that the alloy of the present invention can be obtained in large quantities at low cost. However, in this case, care must be taken during melting because the inclusion of carbon in the graphite crucible causes a decrease in the transformation temperature of the alloy.

Effects of the Invention The shape memory alloy according to the present invention has a shape recovery temperature higher than that of the Ti-Ni alloy, that is, 322K to 861K, by adjusting the PD concentration within the Pd concentration range. It can be applied at any temperature within the range. Moreover, this shape recovery temperature is not affected by heat treatment.

Therefore, the alloy of the present invention is suitably used in application fields that require shape recovery in a higher temperature range than Ti--Ni alloys.

[Brief explanation of drawings]

FIG. 1 is a chart showing the influence of Pd concentration on each transformation temperature in the alloy of the present invention.

Claims (1)

[Claims] 1 Ti: 48.5 to 50.4 at% and Pd: 15 at% or more
Ti-Pd- containing less than 50 atomic % with the balance being Ni
Ni shape memory alloy.