JPH0665740B2 - Method for manufacturing NiTi-based shape memory material - Google Patents

Description

The present invention relates to a method for manufacturing a NiTi-based shape memory material, particularly a shape memory material exhibiting a reversible shape memory effect.

An NiTi alloy containing Ni and Ti in an atomic ratio of about 1: 1 or an alloy in which a part of the Ni or Ti content of the alloy is replaced with a transition metal causes martensitic transformation, which is accompanied by Shows a unique phenomenon called shape memory effect. The shape memory effect is a constant shape above the martensite transformation temperature (hereinafter abbreviated as high temperature), and after it is deformed below the martensite transformation temperature (hereinafter abbreviated as low temperature), it becomes a constant shape at high temperature. It is a phenomenon of recovery.

Such shape memory effect is usually an irreversible phenomenon, and when the shape memory material deformed at low temperature is heated, it recovers to a constant shape at high temperature. I can't go back to. However, from the viewpoint of using the shape memory material as a functional element, it is desirable to remember both the high temperature shape and the low temperature shape and to repeatedly and reversibly operate with respect to the temperature cycle. Therefore, various efforts have been made to reversibly operate the shape memory material, and one of them is a method of giving the shape memory material itself a reversible shape memory effect.

In order to obtain the reversible shape memory effect, the shape memory material is subjected to strong working with a certain amount of strain by cold deformation, or it is subjected to heat treatment while being mechanically constrained while adding the amount of strain due to cold deformation. It is known that However, none of them can accurately set the steady state at high temperature and low temperature, and have not been put to practical use.

As a result of various studies in view of this, the present invention has found that a steady state at high temperature and low temperature can be accurately set by combining controlled cold deformation and heat treatment, and exhibits a reversible shape memory effect. A method for manufacturing a NiTi-based shape memory material was developed. An alloy consisting of Ni 49.2 to 51.5 at% and the balance Ti, or an alloy in which any of Ni and Ti contents of the alloy is replaced with a transition metal of 3% or less is used. , 5 to 120 cold annealing at 350 to 1000 ℃, and then add deformation strain by deformation, in manufacturing shape memory material, add 8 to 20% deformation strain by cold deformation, It is characterized in that the heat treatment is carried out at a temperature 5 to 20 ° C. higher than the temperature at which the temperature reaches a high temperature steady state by extending the amount of change in the rapid change portion of the deformation recovery amount when the temperature is constrained and unheated. It is a thing.

That is, the present invention is a NiTi alloy having the above composition range according to a conventional method.
Annealing treatment is performed at a temperature of 350 to 1000 ° C. for 5 to 120 minutes, and a deformation strain amount of 8 to 20% is added by cold deformation, and the strain amount is restricted as it is. This is heat-treated at a temperature 5 to 20 ° C. higher than the following temperature.

This temperature is 8% due to cold deformation of the annealed NiTi alloy.
When a deformation strain amount of ~ 20% is added and the temperature is raised as shown in the first step, a gradual change from the low temperature steady state (1) (2)
Then, a rapid change (3) occurs, and after a gradual change (4), the high temperature steady state (5) is reached. This rapid change (3) is extended linearly to reach a high temperature steady state.
The temperature is _one point of Af, and heat treatment is performed at a temperature 5 to 20 ° C. higher than this temperature.

However, the reason why the composition of the NiTi alloy is limited as described above in the present invention is to obtain a good shape memory effect,
If it is out of this range, a good reversible shape memory effect cannot be obtained. Moreover, the reason why this alloy is annealed at a temperature of 350 to 1000 ° C. for 5 to 120 minutes is to remove the strain generated in the manufacturing process of the shape memory material. If it exceeds, the shape memory effect is deteriorated due to the coarsening of crystal grains. It should be noted that as the annealing temperature is higher, the strain amount due to the subsequent cold deformation is increased, and good results are obtained.

After annealing, 8-20% of deformation strain is added by cold deformation, and the strain amount is restrained as it is and 5-20 ° C from the temperature of Af ₁ point.
The heat treatment at a high temperature is to obtain a reversible shape memory effect and to accurately set the steady state at high temperature and low temperature. It is difficult to set the state accurately. In particular, when the deformation strain amount is less than 8%, the shape memory effect becomes unclear. The Af ₁ point is about 40 ° C higher than the martensite reverse transformation temperature (Af) of the shape memory material.

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

Fig. 2 shows that a wire made of Ti-49.6at% Ni alloy with a diameter of 1.0mm was annealed at a temperature of 950 ° C for 60 minutes and then strained at room temperature.
The figure shows the thermal expansion curve of a shape-memory material in a 6.6% tensile-deformed and strongly-worked state. As is clear from the figure, as the shape-memory material is heated, the length of the shape-memory material becomes a low temperature steady state (1 ), A gradual contraction (2) occurs, then a rapid contraction (3) in the direction of the arrow occurs, and then a gradual contraction (4) again occurs to reach the high temperature steady state (5). The point at which the high temperature steady state (5) is reached by extending the change in the portion that causes the rapid contraction (3) is defined as the Af ₁ point. Although Af ₁ point is not shown in the figure, it is located on the high temperature side of about 40 ° C. or more from the martensite reverse transformation temperature Af of the shape memory material. Next, when the temperature is lowered, a rapid expansion (6) in the arrow direction is caused from a temperature of about 50 ° C., and then a low temperature steady state (7) is reached. The point at which the high temperature steady state (5) is reached by extending the change in the portion causing the rapid expansion (6) is defined as the Ms point. The temperature rises again, and then a rapid contraction (8) in the arrow direction occurs at a temperature lower than the temperature at which contraction (3) occurs due to the first temperature rise, and then a high temperature steady state (5) occurs. The point at which the rapid change in contraction (8) is extended to reach the high temperature steady state (5) is defined as Af ₂ . After that, if the temperature is lowered and the temperature is raised repeatedly, the rapid expansion (6) in the arrow direction and the contraction (8) in the arrow direction are repeated, which shows a so-called reversible shape memory effect, and Af ₁ point and Ms point. Contracts and expands at.

However, the position of the low temperature steady state (1) at the beginning and the low temperature steady state (7) during repeated operation of the reversible shape memory effect due to such strong working are different from each other. It is difficult to set it in place.

Fig. 3 shows the same wire rod as in Fig. 2 at a temperature of 950 ℃.
Minutes after annealing, the 16.6% of the tensile deformation in the strain amount was added at room temperature to mechanically fixed directly across the Af ₁
The thermal expansion curve of the shape memory material heat-treated at the same temperature as the point is shown. When the shape memory material is heated, it shrinks from the low temperature steady state (1) in the direction of the arrow (2) in the same manner as in FIG.
(3) and (4) are caused to become a high temperature steady state (5), and as the temperature is lowered, expansion (6) in the arrow direction is caused to become a low temperature steady state (7). When the temperature is raised again, contraction (8) in the direction of the arrow occurs and a high temperature steady state (5) is reached, and thereafter, when the temperature is lowered and the temperature is repeated, expansion (6) and contraction (8) in the direction of the arrow are repeated.

What is noticeable in this reversible shape memory effect is that the positions of the low temperature steady states (1) and (7) are close to each other.

Fig. 4 shows the same operation as in Fig. 3, but after tensile deformation of 16.6% in strain at room temperature, mechanically fixing both ends to Af.
The thermal expansion curve of the shape memory material heat-treated at a temperature of ₁ + 10 ° C is shown. As in the case of Fig. 3, the first temperature rise causes a contraction (2) in the arrow direction from the low temperature steady state (1),
The high temperature steady state (5) is brought about by causing (3) and (4), and thereafter, the expansion (6) and the contraction (8) in the arrow direction are repeated by repeating the temperature decrease and the temperature increase. What is noticeable in this reversible shape memory material is that the positions of the low temperature steady states (1) and (7) are almost the same.

Fig. 5 shows the strain amount 1 at room temperature by the same operation as in Fig. 3.
After tension deformation of 6.6%, mechanically fix both ends to Af ₁ +25
The thermal expansion curve of the shape memory material heat-treated at a temperature of ℃ is shown. As in the case of FIG. 3, the initial temperature rise causes a contraction (3) in the arrow direction from the low temperature steady state (1) to a high temperature. The steady state (5) is reached, and thereafter, expansion (6) and contraction (8) in the arrow direction are repeated by repeating the temperature decrease and temperature increase. What is noticeable in this reversible shape memory material is that the low temperature steady state (7) is at a higher position than the low temperature steady state (1).

When heat treatment was performed at Af + 10 ° C. while changing the strain amount at room temperature, the reversible shape memory effect became unclear even when the strain amount was less than 8% or more than 20%. When heat treatment was performed at various temperatures with a strain amount of 15%, Af ₁ + 5 ° C to Af ₁ +20
It was not possible to match the low temperature steady state outside the temperature range of ℃.

As is clear from FIGS. 2 to 5, 8 to 8 due to cold deformation.
Add 20% deformation strain and constrain the strain as it is, Af ₁ +
It can be seen that the shape memory material of the present invention heat-treated in the temperature range of 5 to 20 ° C. exhibits a good reversible shape memory effect and can be installed in a steady state at low temperature accurately.

The above shows the case of Ti-49.6 at% Ni alloy.
Ni alloy and Fe, Cr, Mn, Co,
The thermal expansion curve of the shape memory material manufactured by the method of the present invention for the alloy substituted with any one kind or two or more kinds of Pd etc. was also obtained, and the same result as in FIG. 4 was obtained.

As described above, according to the present invention, it is possible to easily provide a NiTi-based shape memory material that has a good reversible shape memory effect and that can be easily set in a low temperature steady state, and has a remarkable effect industrially. Is.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the relationship between the temperature rise and the deformation of the NiTi-based shape memory material, and FIGS. 2 to 5 are the thermal expansion curves of the NiTi-based shape memory material. FIG. 2 shows the shape memory material according to the conventional method, FIGS. 3 and 5 show the shape memory material according to the comparative method, and FIG. 4 shows the shape memory material according to the method of the present invention. (1) (7) ...... Low temperature steady state (3) (8) ...... Rapid contraction (5) ...... High temperature steady state (6) ...... Rapid expansion

Claims (1)

[Claims] 1. An alloy consisting of 49.2 to 51.5 at% Ni and the balance Ti or an alloy in which any of Ni and Ti contents of the alloy is replaced by 3% or less of a transition metal, at a temperature of 350 to 1000 ° C. After annealing for ~ 120 minutes, in the production of shape memory material that adds deformation strain by cold deformation, 8-20% of deformation strain amount is added by cold deformation and the strain amount is constrained as it is. A method for producing a NiTi-based shape memory material, characterized in that heat treatment is performed at a temperature that is 5 to 20 ° C. higher than the temperature at which a high temperature steady state is reached by extending the rapid change amount of the deformation recovery amount when the temperature is raised.