JPH059687A - Production of two-directional shape memory niti alloy - Google Patents

Abstract

PURPOSE:To remarkably improve the two-directional characteristics of a two- directional shape memory NiTi alloy used for an actuator, etc., and the durability under a temp. cycle. CONSTITUTION:An NiTi alloy consisting of, by atom, 49.5-51.5% Ni and the balance Ti or 38.2-52.0% Ni, <=12% Cu and the balance Ti is subjected to shape memory treatment and 6-13% deformation strain is imposed in an environment at a temp. of the Ms point + 30 deg.C or below to produce a two-directional shape memory NiTi alloy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a bidirectional NiTi type shape memory alloy having excellent bidirectionality and durability.

[0002]

2. Description of the Related Art Shape memory alloys have a cubic crystal structure in the parent phase of a high temperature phase, and when cooled, they transform at the martensite transformation temperature and have a monoclinic structure martensite phase (hereinafter M phase). Becomes When this alloy is heated, it undergoes reverse transformation and returns to the parent phase via the reverse transformation temperature. When the Ni-Ti alloy is subjected to ordinary casting, hot working, cold working and then subjected to shape memory treatment, the operation of the shape memory alloy is irreversible. That is, when the alloy deformed in the martensite phase is heated to a high temperature and transformed into a high temperature phase, the shape recovers, but even if the alloy is cooled, the shape does not return to the low temperature phase. However, it is known that a bidirectional characteristic can be obtained by performing a special process such as a training method in which the strain amount is recoverable and the temperature cycle is added. However, in the conventional method, two directions could not be stably obtained due to complicated processing. Also, the amount of bidirectional strain is as small as 3% or less, and when used as an actuator for energizing a robot,
It was a big problem. As described above, the shape memory alloy is used as an actuator instead of a motor or a solenoid. In this case, heating the alloy by directly energizing it,
Causes shape change. Therefore, a major feature is that it can be made smaller than a motor or solenoid. But,
This application is currently used only partly, and the main reason for this is that the amount of strain of shape change is small and the durability with repetition is poor.

[0003]

In order to solve the above-mentioned problems of the prior art, the present invention provides a bidirectionality with a strain amount of 4% or more, a simple processing step, and a repetitive shape by temperature cycle. The present invention provides a manufacturing method capable of obtaining a Ni—Ti-based shape memory alloy having excellent recovery durability.

[0004]

SUMMARY OF THE INVENTION The present invention is directed to atomic percent Ni.
After shape memory treatment of a NiTi-based alloy composed of 49.5 to 51.5% balance Ti at a temperature of 500 to 800 ° C.,
A method for producing a bidirectional NiTi-based shape memory alloy, characterized in that a deformation strain of 6 to 13% is applied in a temperature environment of Ms point + 30 ° C. or lower, is claim 1, and Ni 38.2 in atomic% is used.
~ 52.0%, Cu 12% or less NiT consisting of the balance Ti
A bidirectional NiTi-based shape memory characterized by applying a deformation strain of 6 to 13% in a temperature environment of Ms point + 30 ° C. or less after performing shape memory treatment on an i-based alloy at a temperature of 500 to 800 ° C. A method for producing an alloy is defined as claim 2.

[0005]

That is, according to the present invention, the NiTi alloy having the above composition is processed into a predetermined shape, and the shape memory treatment is performed at 500 ° C. or higher.
It is characterized in that a deformation strain of 6% or more and 13% or less is given in a temperature environment of Ms point + 30 ° C. or less by performing the temperature at 00 ° C. or less. Especially for wire materials, shape memory processing is performed linearly under the same conditions, and in a temperature environment of Ms point + 30 ° C or less,
By giving a tensile deformation strain of 6 to 13% in the longitudinal direction, it is possible to obtain an alloy wire rod that is shortened by 4% or more at high temperature as compared with at low temperature. The composition range of the alloy targeted by the present invention is a NiTi-based shape memory alloy composed of 49.5 to 51.5% of Ni in atomic% and the balance of Ti. Also,
By applying the manufacturing method of the present invention to a NiTi-based shape memory alloy consisting of 38.0 to 52.0% Ni in atomic% and 12% or less Cu, and the balance Ti, the martensitic transformation temperature during cooling and the heating time A two-way shape memory alloy is obtained in which the temperature, which is the difference between the reverse transformation temperatures, and hysteresis are narrower than those of the Ni-Ti binary alloy. If the memory heat treatment temperature is less than 500 ° C., sufficient bidirectional strain cannot be obtained. Also 800 ° C
If it exceeds, the oxidation of the alloy surface becomes severe, which is not preferable in terms of material. If the deformation strain amount after shape memory processing is less than 6%, sufficient bidirectional strain cannot be obtained, and if it exceeds 13%, the recovery strain amount decreases significantly. The deformation temperature is preferably lower than the Ms temperature, and when it exceeds Ms + 30 ° C, it is 2
The amount of directional distortion is reduced. If the Ni content is less than 49.5% or more than 51.5%, the workability deteriorates, which is not industrially preferable. In the Ni-Ti-Cu alloy, the Ni content is 3
If it is less than 8.2% or more than 52.0% and Cu exceeds 12%, the workability is similarly deteriorated.

[0006]

【Example】

[Embodiment 1] Next, an embodiment of the present invention will be described. Alloys having the compositions shown in Table 1 were cast, hot-worked, and then repeatedly annealed and cold-worked to produce an alloy wire having a wire diameter of 1 mm.

[0007]

[Table 1]

This alloy was subjected to a linear memory heat treatment under the treatment conditions shown in Tables 2 and 3. Further, tensile deformation was applied by a tensile tester at an atmospheric temperature controlled by a constant temperature bath as shown in Tables 2 and 3. The transformation temperature Ms and As point of the alloy before deformation were determined by the DSC method. A weight corresponding to a constant load of 1 kgf / mm ² which is a stress for stabilizing the alloy wire to attach an extensometer is applied to the treated alloy wire, and a temperature cycle test is performed at a speed of 3 ° C / min. The change in strain was measured with a strain gauge type extensometer. The obtained temperature-strain curve is shown in FIG. As shown in the figure, the As point, the Ms point, and the bidirectional shape recovery strain amount were determined. The results are shown in Tables 2 and 3. In the comparative example in the table, the bidirectional strain amount does not reach 4% or more because either the shape memory processing temperature of the present invention or the deformation strain imparting condition is lacking.

[0009]

[Table 2]

[0010]

[Table 3]

Sample No. The relationship between the tensile deformation strain amount and the bidirectional strain amount in 2 to 7 is shown in FIG. 6 from this figure
It is clear that a tensile deformation strain of 13% to 13% gives a bidirectional strain amount of 4% or more. 3 and 4 show the relationship between deformation temperature and bidirectional strain. In FIG. 3, alloy B
No. No. 11 to 16 and alloy C. 19 ~ 22 results,
In FIG. 4, alloy D No. The results of 22 to 25 are described. In each case, the horizontal axis represents the temperature difference between the deformation temperature and the Ms point. It is clear that when the deformation temperature exceeds Ms + 30 ° C., the bidirectional strain is extremely reduced. Therefore, a deformation temperature of Ms + 30 or less is desirable. Further, it can be seen that the temperature hysteresis in the bidirectionality of alloy D is narrower than that of the Ni-Ti base alloy. [Example 2] For an alloy wire of 0.15 mm of alloy A, N
o. Under the same trial production method as in No. 4, a repeated temperature cycle test was performed on a Ni—Ti alloy wire rod that was subjected to tensile deformation for two directions and a sample that was not subjected to tensile deformation as a comparative material. No. 0.15mm under the same manufacturing conditions as 24
The wire having the same wire diameter was also subjected to the test. The length of the line is 20
It was set to 0 mm, the upper part was fixed, and a 275 g weight was hung. An ON-OFF operation was performed by heating by applying a DC current of 0.5 A to the alloy wire. Energization interval is 5
Seconds. And the position of the weight in each repetition number was measured. The results are shown in FIG. The durability was defined by the following formula. The vertical axis of FIG. 5 shows this durability, and the horizontal axis shows the number of repetitions. No. by the method of the present invention 4 and No. It is clear that the sample No. 24 is superior in durability due to the temperature cycle as compared with the comparative material.

[0012]

As described above, according to the present invention, N
The iTi-based shape memory alloy is an alloy that has excellent bidirectional characteristics and durability due to temperature cycling, and can be applied as a compact actuator in place of a motor or solenoid. Have.

[Brief description of drawings]

FIG. 1 is a graph showing strain-temperature characteristics of a bidirectional NiTi-based shape memory alloy according to an example of the present invention.

FIG. 2 is a graph showing the relationship between bidirectional strain and deformation strain of a bidirectional NiTi-based shape memory alloy according to an example of the present invention.

FIG. 3 is a graph showing the relationship between bidirectional strain and deformation temperature of a bidirectional NiTi-based shape memory alloy according to an example of the present invention.

FIG. 4 is a graph showing the relationship between bidirectional strain and deformation temperature of a bidirectional NiTi-based shape memory alloy according to an example of the present invention.

FIG. 5 is a graph showing the relationship between the durability and the energization cycle of the bidirectional NiTi-based shape memory alloy according to an example of the present invention.

Claims (2)

[Claims] 1. A NiTi-based alloy having an atomic percentage of Ni of 49.5 to 51.5% and a balance of Ti is subjected to shape memory treatment at a temperature of 500 to 800 ° C., and then 6 to 6 at a temperature environment of Ms point + 30 ° C. or less. A method for manufacturing a bidirectional NiTi-based shape memory alloy, which is characterized by imparting a deformation strain of 13%. 2. Ni38.2-52.0%, C in atomic%
u12% or less 500 NiTi-based alloy consisting of the balance Ti
After shape memory treatment at a temperature of ~ 800 ° C, Ms point +
A method for producing a bidirectional NiTi-based shape memory alloy, which comprises imparting a deformation strain of 6 to 13% in a temperature environment of 30 ° C. or lower.