JPS622027B2 - - Google Patents

Description

[Detailed description of the invention] The present invention has two phases: a TiNi phase and a TiNi ₃ phase.
After solution treatment in a temperature range of 500 to 1100℃ and aging treatment in a temperature range of 200 to 700℃ to a Ti-Ni alloy with excessive Ni composition, recrystallization does not occur at temperatures above 200℃. Warm processing with
The present invention also relates to a method for manufacturing a Ti-Ni superelastic alloy, which is heat-treated without causing recrystallization after warm working, thereby making it difficult to cause slip deformation due to the movement of dislocations and significantly improving the superelastic properties. be.

Ti-Ni exhibits thermoelastic martensitic transformation
and Ti-Ni-X (hereinafter referred to as Ti-Ni alloy)
is known to exhibit good superelastic alloys and shape memory effects, and studies are underway to utilize these properties in various applications.

Superelasticity is characterized by stress-induced martensitic transformation caused by external stress, resulting in apparent plastic deformation of more than ten percent, and when the stress is removed, the material returns to its original shape through reverse transformation. . Such superelasticity is generally evaluated by the magnitude of stress hysteresis and the critical stress at which no sliding deformation occurs, and it is said that the smaller the stress hysteresis and the higher the critical stress at which no sliding deformation occurs, the more desirable. Therefore, it is necessary to make it difficult to cause slip deformation due to the movement of dislocations. However, as conventional superelastic alloys, alloys with a composition of 50.0 to 51.0 at% Ni are selected depending on the operating temperature, and this alloy is used after being heat treated at a high temperature of about 1000°C. As a result, recrystallization occurs and dislocations become more mobile, which has the disadvantage that the critical stress at which slip deformation does not occur is low.

Recently, in Ti-Ni alloys with excessive Ni composition, solution treatment and aging treatment cause the precipitation of TiNi ₃ particles, which increases the critical stress at which no sliding deformation occurs, and improves superelastic alloy properties. It was reported that the improvement [Bulletin of the Japan Institute of Metals, Vol. 22,
33 (1983)].

Although this method of using precipitated particles to prevent slip deformation from occurring is very effective, it is possible for dislocations to slip between the precipitated particles in the initial stage of loading, and in order to obtain excellent superelasticity. It is also necessary to prevent the movement of dislocations.

On the other hand, recently, a method has been announced in which heat treatment is performed at a temperature of 250°C or higher without causing recrystallization after cold working, in order to make it difficult for dislocations to move and increase the critical stress that does not cause slip deformation (Japanese Patent Application Laid-Open No. 161753/1983). (see publication).

The purpose of this method is to add processing such as cold rolling and drawing to create a processed structure that is less prone to slip deformation. However, Ti--Ni alloys have extremely poor workability, especially cold workability, so the degree of workability is limited to about 20% at most. For this reason, it is difficult to uniformly obtain a processed structure in the alloy that sufficiently inhibits the movement of dislocations and makes slip deformation difficult to occur.

From this point of view, the present inventors investigated a method with the aim of obtaining a uniform processed structure in the alloy that is unlikely to undergo sliding deformation due to the movement of dislocations, as well as the pinning effect of dislocations by precipitated particles, and found the following results: They have found a way to have a beneficial effect.

In other words, the method of the present invention involves adding 500% to a Ti-Ni alloy with a Ni-excess composition and having two phases: a TiNi phase and a TiNi _three phase.
Solution treatment in the temperature range of ~1100℃ and 200~
After aging treatment in the temperature range of 700℃, 200℃
It is characterized by warm working without causing recrystallization at a temperature above 100%, and heat treatment after warm working without causing recrystallization. This makes it difficult for sliding deformation due to the movement of the metal to occur, making it possible to obtain an excellent superelastic alloy.

Note that the warm working in the present invention is to obtain a sufficient processed structure that cannot be obtained by cold working, and is carried out at a temperature that does not cause recrystallization in order to prevent the movement of dislocations and make slip deformation difficult to occur. There is a need. Further, for the same reason, the heat treatment after warm working must be performed at a temperature that does not cause recrystallization.

Next, the reasons for limiting the processing conditions in the present invention will be described.

Regarding the solution treatment temperature, if the temperature is lower than 500℃, sufficient solid solution of TiNi ₃ cannot be obtained in the TiNi matrix, and enough TiNi ₃ particles can be precipitated to prevent the movement of dislocations during the next aging treatment. do not have. Furthermore, when the temperature exceeds 1100°C, loss of Ti element due to oxidation becomes a problem. From the above point of view, the temperature range was limited to 500 to 1100°C.

Regarding the aging treatment temperature, sufficient precipitation of TiNi ₃ particles does not occur at temperatures below 200℃, and at temperatures below 700℃.
If the temperature exceeds 100%, over-aging occurs and the TiNi ₃ precipitated particle-matrix interface loses integrity, making it impossible to sufficiently prevent dislocation movement. From the above point of view, the temperature range was limited to 200 to 700°C.

As for the warm working temperature, at temperatures below 200°C, it is difficult to obtain a sufficient processed structure to prevent slip deformation due to large deformation resistance, and at temperatures where recrystallization occurs, dislocations move. This is considered to be easy, and good superelasticity cannot be obtained.

Although the effect of warm working is recognized even at a degree of working of a few percent, working to a degree of 30% or more is desirable in order to obtain a sufficient working structure that cannot be obtained with cold working. In addition, the temperature at which recrystallization does not occur during warm working and heat treatment after warm working is
The temperature is preferably around 500°C, but good superelasticity can be obtained even at temperatures higher than this in the case of short-time treatment without recrystallization.

The present invention will be explained below based on examples.

Example 1 A Ti-50.7at%Ni alloy with a Ni-excess composition having two phases, a TiNi phase and a TiNi ₃ phase, was subjected to high-frequency induction melting in argon, and then vacuum annealed at 1000°C for 2 hours to homogenize it. After that, it was forged at 900℃ to make a 12φ rod. This rod was further processed to 4φ by hot swaging, and then heated to 850°C for 2 hours.
It was subjected to time solution treatment and cooled in water. Next, the wire was aged at 500°C for 2 hours, and then warm wire drawn at 400°C to obtain a 1φ wire, and a portion of the wire was used as a tensile test piece. After that, add 200 to the remaining alloy (1φ wire).
℃, 400℃ and 550℃ for 1 hour to obtain a tensile test piece.

Figure 1a shows the stress-strain curve in the warm wire drawing state. For comparison, alloys made using conventional methods include an alloy that was heat-treated at 400°C for 1 hour after cold working, and an alloy that was solution-treated at 850°C for 2 hours and then aged at 500°C for 2 hours. The stress-strain curves of the alloy heat-treated at 1000°C for 1 hour are shown in Figures 1b, c, and d.

As is clear from the figure, the alloy heat-treated at 1000°C for 1 hour suffers permanent deformation due to sliding deformation, as shown in d, and does not return to its original shape, whereas the alloy prepared by the method of the present invention suffers from permanent deformation, as shown in a. No permanent deformation was observed, and excellent superelasticity was obtained.
In addition, alloys heat treated at 400℃ for 1 hour after cold working and 500℃ after solution treatment at 850℃ for 2 hours.
The alloys treated at ℃ for 2 hours have relatively good superelasticity as shown in b and c, but the critical stress at which no sliding deformation occurs is lower than that of the alloy of the present invention, and the stress hysteresis is also large. It's summery.
It is clear from this that the superelasticity of the alloy produced by the method of the present invention is very excellent.

Figure 2 a, b, c are respectively 200℃, 400℃ and
The stress-strain curve of the alloy heat-treated at 550°C for 1 hour is shown.

As is clear from the figure, excellent superelasticity is obtained as shown in a and b in heat treatments at 200°C and 400°C, where no recrystallization is considered to have occurred, but at 550°C, recrystallization occurs. As shown in c, permanent deformation is observed and it is no longer possible to return to the original shape.

Example 2 A Ti-51.0at%Ni alloy was made into a 1φ wire in the same manner as in Example 1, and then heat treated at 300° C. for 1 hour to obtain a stress-strain curve. The results are shown in Figure 3a. For comparison, the following alloys were prepared using the conventional method: an alloy heat-treated at 400°C for 1 hour after cold working, an alloy aged at 850°C for 2 hours, and an alloy heat-treated at 1000°C for 1 hour. The stress-strain curves are shown in Figure 3b, c, and d.

As is clear from the figure, the alloy produced by the method of the present invention is thought to be less prone to slip deformation due to the movement of dislocations than the alloy produced by the conventional method, has a high critical stress at which slip deformation does not occur, has small stress hysteresis, and has excellent superelasticity. is obtained.

As described in the examples above, the method of the present invention has the effect of pinning dislocations due to precipitated particles, and at the same time prevents the movement of dislocations within the alloy and creates a processed structure in which slip deformation is difficult to occur, thereby producing an excellent superelastic alloy. This makes it possible to obtain this material, and it is extremely useful for applications such as spring materials.

[Brief explanation of the drawing]

FIG. 1a is a diagram showing the stress-strain curve of a superelastic alloy produced by the method of the present invention, and FIGS. 1b, c, and d are diagrams depicting the stress-strain curve of a superelastic alloy produced by the conventional method.
Figures 2a and b are diagrams showing the stress-strain curves of the superelastic alloy produced by the method of the present invention, Figure 2c is a diagram showing the stress-strain curve when recrystallization is caused, and Figure 3a
Figure 3b, c and d are diagrams showing stress-strain curves of superelastic alloys produced by the method of the present invention, and Figures 3b, c and d are diagrams showing stress-strain curves of superelastic alloys produced by the conventional method.

Claims (1)

[Claims] 1. A Ti--Ni alloy with a Ni-excess composition having two phases, a TiNi phase and a TiNi ₃ phase, is subjected to solution treatment in a temperature range of 500 to 1100°C, followed by rapid cooling treatment, and then quenched at a temperature of 200°C. It is characterized by being subjected to aging treatment in a temperature range of ~700°C and then warm working at a temperature of 200°C or higher without causing recrystallization.
Manufacturing method of Ti-Ni superelastic alloy. 2. A Ti-Ni alloy with a Ni-excess composition having two phases, a TiNi phase and a TiNi ₃ phase, is subjected to solution treatment in a temperature range of 500 to 1100°C, followed by rapid cooling treatment, and then in a temperature range of 200 to 700°C. After aging treatment at , warm working is performed at a temperature of 200°C or higher without causing recrystallization, and then further heat treatment is performed without causing recrystallization.
Manufacturing method of Ti-Ni superelastic alloy.