JPS622028B2 - - Google Patents

Description

[Detailed description of the invention] The present invention has two phases: a TiNi phase and a TiNi ₃ phase.
500 to 1100 for Ti-Ni shape memory alloys with excessive Ni composition
High-temperature phase →
The present invention relates to a method for producing a Ti--Ni shape memory alloy, which is characterized by obtaining a shape memory alloy with extremely small transformation hysteresis in the low-temperature phase.

Ti--Ni shape memory alloys are the ones that are being studied most extensively for practical use because they exhibit a remarkable shape memory effect and have excellent mechanical properties, corrosion resistance, etc.

The shape memory effect occurs when a material that is in a martensitic state at low temperatures is deformed and then returns to its original shape when heated. The temperature at which this effect occurs is usually the reverse transformation start temperature (As point) and the reverse transformation end temperature (A point) of the alloy. Af
The shape memory effect starts at the As point and ends at the Af point. The recovery force when producing this shape memory effect ranges from 50 to 60 kg/mm ² , and studies are being made to utilize this recovery force in various applied products. A typical example of its application is an actuator that utilizes the repeated generation of a shape memory effect, as shown in Figure 1. This actuator is a combination of a normal coil spring (bias spring) as a bias force and a shape memory alloy coil spring.At low temperatures, the shape memory alloy enters a martensitic phase state with a lower yield stress than the bias spring. Therefore, the bias spring is stronger and acts to deform the shape memory alloy, and conversely, at high temperatures, the shape memory alloy enters the β phase state with a higher yield stress than the bias spring, and the shape memory alloy becomes biased. It works to deform a spring. In this case, the smaller the transformation hysteresis from the high temperature phase to the low temperature phase, the easier it is to operate as an actuator in a small temperature range.

However, in conventional Ti-Ni alloys, the transformation hysteresis from high-temperature phase to low-temperature phase is as large as about 30°C, so the temperature range in which the actuator operates by reversibly obtaining the low-temperature phase and the high-temperature phase is difficult. Unavoidably, this had the disadvantage that the operating temperature range was limited.

From this point of view, the present inventors developed a two-phase TiNi phase and a TiNi ₃ phase in order to obtain an alloy that has a small transformation hysteresis from high temperature phase to low temperature phase and facilitates the operation of the actuator as shown in Figure 1. with Ni
It has been discovered that beneficial effects can be brought about when the treatment described in the claims is applied to a Ti--Ni type shape memory alloy with an excessive composition. In other words, supersaturated Ni becomes TiNi ₃ through solution treatment and aging treatment.
It becomes particles and precipitates in the matrix, and along with this, an intermediate phase transformation is introduced, and the transformation occurs in two stages, and the transformation from high temperature phase to low temperature phase (intermediate phase) becomes extremely small.

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

Regarding solution treatment temperature below 500℃
It is thought that sufficient solid solubility of TiNi ₃ in the TiNi matrix cannot be obtained, and its effect is not sufficiently recognized. Furthermore, when the temperature exceeds 1100°C, loss of Ti element due to oxidation becomes a problem. 500~ from the above point of view
The temperature range was limited to 1100℃.

Regarding the aging treatment temperature, sufficient precipitation of TiNi ₃ particles does not occur at temperatures below 200°C, and when it exceeds 700°C, intermediate phase transformation cannot be introduced, resulting in a small hysteresis due to the transformation from high temperature phase to low temperature phase (intermediate phase). I won't be able to do it. From the above point of view, the temperature range was limited to 200 to 700°C.

Regarding the memory treatment temperature, at temperatures exceeding 700°C, the shape memory properties deteriorate, and the mesophase transformation disappears, making it impossible to obtain a small hysteresis due to the transformation from high temperature phase to low temperature phase (intermediate phase). From the above point of view
The temperature range was limited to 700℃ or less.

Note that when constraining to a predetermined shape to be memorized before solution treatment and aging treatment, the shape can be memorized by aging treatment, so memory treatment is not required; however, when constraining after aging treatment requires memory processing. Furthermore, as for the timing of constraint to a predetermined shape to be memorized, good results can also be obtained with any of the claims.

The present invention will be explained below based on examples.

Example 1 After high-frequency induction melting of a Ti-50.7at%Ni alloy with Ni-excessive composition having two phases of TiNi phase and TiNi _three phases
Vacuum annealing was performed at 1000°C for 2 hours to homogenize the material, followed by forging at 900°C to obtain a _φ12 bar. This rod was further hot-worked and cold-worked into a wire of _φ1 . Next, this wire was formed into a coil spring as shown in Fig. 1, and after being restrained, it was subjected to solution treatment at 800℃ for 2 hours, and then at 400℃ for 5 hours.
After time aging, the displacement-temperature curve was measured and the transformation point was measured using a differential scanning calorimeter (DSC) to confirm the transformation hysteresis from high temperature phase to low temperature phase (intermediate phase).

Figure 2 shows DSC after aging treatment in Example 1.
The measurement results of the transformation point are shown. In conventional alloys, one DSC peak due to the transformation of the low-temperature phase to the high-temperature phase is observed during heating and one during cooling, whereas in the alloy produced by the method of the present invention, an intermediate phase transformation is introduced, and two peaks are observed during heating and cooling, respectively. It has one peak after another. Along with this, the peak during cooling starts at almost the same temperature as the transformation end temperature during heating, and the transformation hysteresis from the high temperature phase to the low temperature phase (intermediate phase) becomes almost 0°C. Further, FIG. 3 shows a displacement-temperature curve when a constant load is applied to the coil spring of Example 1 by a weight, and it is clear that the hysteresis is extremely small compared to the conventional material. For comparison, the conventional material
The transformation point measurement results and displacement-temperature curves by DSC are shown in FIGS. 4 and 5.

Example 2 A Ti-51.0at%Ni alloy was formed into a φ1 wire in the same manner as in Example ₁ , and then solution treatment was performed at 800° C. for 2 hours. Next, after forming into a coil spring and restraining it by the same method as in Example 1,
Aging treatment was performed at ℃ for 2 hours. FIG. 6 shows the measurement results of the transformation point by DSC after the aging treatment in Example 2. As is clear from the figure, an intermediate phase transformation is observed, and along with this, the transformation hysteresis from the high temperature phase to the low temperature phase (intermediate phase) has a very small value of about 2°C. In this case, the two peaks during heating overlap at approximately the same temperature due to the influence of the aging treatment temperature. Further, FIG. 7 shows a displacement-temperature curve when a constant load is applied to the coil spring of Example 2 by a weight, and it is clear that extremely good hysteresis is obtained compared to the conventional material.

Example 3 A Ti-51.2at%Ni alloy was formed into a φ1 wire in the same manner as in Example ₁ , and then solution treatment was performed at 900° C. for 2 hours. Next, it was aged at 400°C for 10 hours, then molded into a coil spring and restrained in the same manner as in Example 1, and further subjected to memory treatment at 400°C for 30 minutes. The transformation hysteresis from the high temperature phase to the low temperature phase (intermediate phase) at this time was 1°C, and good hysteresis was also confirmed in the displacement-temperature curve of the coil spring.

As described in the examples above, the alloy according to the present invention has an extremely small transformation hysteresis from high temperature phase to low temperature phase (intermediate phase) compared to conventional alloys, and can limit the operating temperature range when used in actuators etc. It is extremely beneficial as it significantly relaxes and at the same time increases thermal responsiveness.

[Brief explanation of the drawing]

Figure 1 shows an actuator using a shape memory alloy, Figure 2 shows the transformation point measurement results of the alloy of Example 1 by DSC, and Figure 3 shows the displacement-temperature curve of the coil spring of Example 1. Figure 4 shows the transformation point measurement result of the conventional alloy by DSC, Figure 5 shows the displacement-temperature curve of the conventional alloy, and Figure 6 shows the transformation point measurement result of the alloy of Example 2 by DSC. The results are shown in FIG. 7, which shows the displacement-temperature curve of the coil spring of Example 2. 1: Coil spring, 2: Shape memory alloy coil spring.

Claims (1)

[Claims] 1. In a Ti--Ni shape memory alloy with a Ni-excess composition having two phases, a TiNi phase and a TiNi ₃ phase, it is constrained to a predetermined shape to be memorized after processing, and then
A method for manufacturing a shape memory alloy, which comprises performing solution treatment in a temperature range of 1100°C, followed by rapid cooling treatment, and then further performing aging treatment in a temperature range of 200 to 700°C. 2 In a Ti-Ni shape memory alloy with a Ni-excessive composition that has two phases, a TiNi phase and a TiNi ₃ phase, after processing
A shape characterized by being subjected to solution treatment in a temperature range of 500 to 1100°C, followed by rapid cooling treatment, then constrained to a predetermined shape to be memorized, and then further subjected to aging treatment in a temperature range of 200 to 700°C. A method for manufacturing memory alloys. 3 After processing in a Ti-Ni shape memory alloy with Ni-excessive composition that has two phases: TiNi phase and TiNi ₃ phase,
After solution treatment in the temperature range of ~1100℃, quenching treatment is performed, then aging treatment is performed in the temperature range of 200 to 700℃, and then restrained to a predetermined shape to be memorized, and then further at a temperature of 700℃ or less. 1. A method for producing a shape memory alloy, the method comprising performing a memory treatment within a range.