JPS60169551A - Manufacture of shape memory alloy - Google Patents

Abstract

PURPOSE:To obtain a shape memory Ti-Ni alloy having bidirectional properties by carrying out soln. heat treatment at a specified temp., quenching, againg, cold working at a specified percentage and memory treatment at a prescribed temp. CONSTITUTION:A shape memory Ti-Ni alloy contg. Ni in excess and having TiNi and TiNi3 phases is subjected to soln. heat treatment at 500-1,100 deg.C, quenching, aging at 200-700 deg.C, cold working at <=60% and memory treatment at <=700 deg.C. By the cold working after the aging, orientation different from that of TiNi3 grains obtd. by only aging under constraint is obtd., so the direction of martensite transformation during cooling is controlled. By this method, satisfactory bidirectional properties are provided to a coil spring or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an 'I' i -Ni type shape memory alloy with a Ni-excess composition having two phases, a T1Ni phase and a T1Ni phase, which is solution-treated in a temperature range of 500 to 1100°C. A post-quenching treatment is performed, followed by an aging treatment at a temperature range of 200 to 700°C, followed by cold working of 60% or less, followed by further storage treatment at a temperature of 700°C or less. ) 'R4+ The present invention relates to a method for manufacturing a shape memory alloy, which is characterized by obtaining a shape memory alloy having a small transformation hysteresis of the mild to low temperature phase and having a bidirectional ul in a coil spring.

Ti--Ni type shape memory alloys exhibit a remarkable shape memory effect and have excellent mechanical properties, corrosion resistance, etc., and are therefore being studied in the widest range for practical use.

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 upon heating.
The shape memory effect starts at the As point and ends at the M point. It is something. The recovery power when creating this shape memory effect is 50-60kl? /g
lI, and studies are being conducted to utilize this resilience in various applied products. The first example of its application is
There is an actuator that utilizes the ability to repeatedly generate a shape memory effect, as shown in the figure. This acticony
The spring is a combination of a regular coil spring (bias spring) and a shape memory alloy coil spring, and at low temperatures the shape memory alloy has a lower yield stress than the bias spring because it is in a martenyite phase state. At high temperatures, the bias spring is stronger and acts to deform the shape memory alloy, and conversely, at high temperatures, the shape memory alloy enters a β-phase state with a higher yield stress than the bias spring, causing the shape memory alloy to deform like the bias spring. It works like that.

In this case, the smaller the high-temperature phase→low-temperature phase transformation hysteresis or the bidirectionality, the easier it is to operate as an actuator in a small temperature range. However, in conventional Ti-Ni alloys, only a unidirectional shape memory effect can be obtained, and the transformation hysteresis from high temperature phase to low temperature phase is as large as approximately 30°C, so the low temperature phase and high wettability phase are reversible. Therefore, the temperature range in which the actuator is operated has to be widened, and the operating temperature range is limited.

On the other hand, recently, in such Ti-NI thread shape memory alloys, Ni 50.3-530% in atomic percent, asT
An alloy with a Ni-excessive composition consisting of r is subjected to heat treatment at 600°C or higher to make it i' i Ni single phase, and then subjected to aging treatment at a temperature of 600°C or lower under mechanical restraint. A method of imparting a reversible shape memory effect by creating a multi-phase structure of a TiN β phase and a TiNi3 phase was announced. (Japanese Unexamined Patent Publication No. 58-151445) However, the reversible shape memory effect by this method can only be obtained when a strip-shaped sample is restrained as shown in Figure 2. When applied to a coil spring as shown, no reversible shape memory effect is observed.

From this point of view, the present inventors have developed a T1Nβ phase, a T1Ni phase, and a T1Ni phase alloy in order to easily operate the actuator as shown in FIG. A Ti-Ni-based shape memory alloy with a Ni-excessive composition having two phases is subjected to solution treatment at a temperature range of 500 to 1100 °C, followed by rapid cooling treatment, and then aging treatment at a temperature range of 200 to 700 °C. It has been discovered that a beneficial effect can be obtained by subjecting the material to a cold working process of 60% or less, followed by further memory treatment at a temperature of 700''C or less.

In the present invention, cold working after aging treatment is performed to remove Ti precipitated in the matrix by solution treatment and aging treatment.
The purpose is to align the orientation of the N i 3 particles in the processing direction, and the T
1Ni, an orientation different from that of the particles can be obtained. As a result, the direction of formation of martenzite transformation during cooling is restricted, and good bidirectionality can be obtained in the fill spring, which cannot be obtained by restrained aging treatment. In addition, supersaturated Ni is reduced by aging treatment after solution treatment.
iNi becomes particles and deposits in the matrix/Ji L
, along with this. An intermediate phase transformation is introduced and the transformation occurs in two stages, and the transformation hysteresis from the high temperature phase to the low wetness 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''C.

is '1' 1Ni into 'I' i N i matrix
It is considered that a sufficient solid solubility of No. 3 cannot be obtained, and its effect cannot be sufficiently maintained. Moreover, if the temperature exceeds 1100°C, loss of TI elements due to oxidation becomes a problem. From the above point of view, the temperature range was limited to 500 to 1100°C.

As for l-Sor treatment temperature, if the temperature is less than 200°C, sufficient precipitation of T1Ni and O'12 molecules will not occur, and if it exceeds 10°C, intermediate phase transformation will not be introduced.
A small hysteresis during the transformation from high temperature phase to low temperature phase (intermediate phase) becomes difficult to obtain. From the above point of view, 200-700'
The temperature range was limited to C.

The effect of cold working C1 is not noticeable even if it is only a few percent of cold working, but 'I' precipitated in 7-trinox.
It is necessary to obtain as large a processing degree as possible from the point of view of aligning the orientation of the grains i and the processing direction. However, in terms of machining rate exceeding 2 or 6 [)%, is it possible to process alloys? Since this phenomenon becomes noticeable and the formability during the next memory boiling is impaired, it is desirable to take this point into account when determining the degree of processing.

For one memory treatment wash, the shape memory properties deteriorate at temperatures of 700'C or higher, and the mesophase transformation disappears, making it impossible to obtain a small hysteresis during 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°C or less.

The present invention will be explained below based on examples.

[Example 1] A Ti-50,7 at% Ni alloy with a Ni-excess composition having two phases of I''iN1 phase and TiNi3 phase was subjected to high-frequency induction melting in argon and then vacuum annealed at 1000'C for 2 hours. After that, it was forged at 900°C to make a φ12 rod.Then, this rod was hot-worked and cold-worked into a φ10 wire, and then forged at 800°C.
Solution treatment was performed at C for 2 hours and cooled with water. After that G
After aging at 400°C for 10 hours, cold wire drawing was performed to obtain a wire of φ08. After forming this line into a fill spring as shown in Figure 3(d) and performing memory treatment at 400°C for 50 minutes, the presence or absence of bidirectionality and the transformation point using a differential scanning calorimeter (DSC) were determined. We conducted measurements and confirmed the transformation hysteresis from high-temperature phase to low-temperature phase (intermediate phase). The presence or absence of bidirectionality was determined by whether the coil spring was in a close contact state with a memorized shape when heated and spontaneously stretched when cooled, as shown in FIG.

Figure 4 shows the actual example 1 after memory processing])
The results of measuring the transformation point using C are shown. As is clear from the figure, an intermediate phase transformation is introduced and there are two peaks each during heating and cooling. Along with this, the peak during cooling begins at rr::, lψ, which is almost the same as the transformation end temperature during heating, and the change from high temperature phase to low temperature sum (intermediate phase) ρ
(The hysteresis is almost 0°C). City, -
In this state p[S, the coil spring exhibits remarkable bidirectionality (44), and the displacement-temperature curve is shown in Figure 5.
A large spontaneous displacement can be obtained during cooling.

41'For comparison, Figure 5 shows the temperature curve of the fill spring in the case of only the restrained aging treatment.In the coil spring, almost no spontaneous displacement is obtained during cooling, and the method of the present invention It is clear that the alloy coil spring has excellent bidirectional properties.

[Example 2] A Ti-51, Oat%Ni alloy was melted by high-frequency induction in argon and made into a φ12 wire using the same method as in Example 13'lJ1, followed by solution treatment at 900°C for 2 hours. processed. Next, after aging treatment at 500°C for 2 hours, cold wire drawing was performed to obtain a wire of φ08, which was further formed into a coil spring by the same method as in Example 1.
Amnestic treatment was performed at 00°C for 30 minutes.

FIG. 6 shows a displacement-temperature curve, and it is clear that good bidirectionality was obtained in Example 1 as well. In this case, the transformation hysteresis from high temperature phase to low temperature phase (intermediate phase) was 1°C.

[Example 3] 'I'i -51,23t%N1 alloy was subjected to high-frequency induction melting in argon, made into a φ10 wire by the same method as in Example 1, and then melted at 600°C for 2 hours. processing was performed. Next, after aging treatment at 400°C for 5 hours, cold wire drawing was performed to obtain a wire of φ08, which was further formed into a coil spring by the same method as in Example 1, and then 4OO
Amnestic treatment was performed for 1 hour at °C. The prosperity phase at this time →
It was confirmed that the transformation hysteresis iJi of the low-depletion phase (intermediate phase) was 1°C, and that it had remarkable bidirectionality 2).

As described in the examples above, the alloy according to the present invention has extremely small change from high temperature phase to low temperature phase (intermediate phase) + gQ hysteresis compared to conventional alloys. Noticeable bidirectional fl in:
This is extremely beneficial as it significantly alleviates the limitations on the operating temperature range when used in actuators, etc. and at the same time increases thermal responsiveness.

[Brief explanation of drawings]

The first UA shows an actuator using a shape memory alloy. Figure 2 shows the restrained state of a strip-shaped specimen and the behavior of the specimen due to the reversible shape memory effect. (a) shows the restrained shape of the specimen, and (b) and (C) show the state in which it spontaneously assumes a straight-stretched shape upon cooling. This is what is shown. FIG. 5 shows the shape of the coil spring. (d) shows the memorized shape, and (e) shows the state expanded by cooling. Figure 4 shows the alloy of Example 10.
The results of the transformation point measurement are shown. FIG. 5 shows the displacement-dirty curvature curves of the coil spring of the alloy of Example 10 and the coil spring subjected only to restrained aging treatment. FIG. 6 shows the displacement-temperature curve of the coil spring of the alloy of Example 2. 1: fill spring, 2: shape memory alloy coil spring, 3: pipe for restraining the sample, 4: rectangular shape memory alloy, 5゛wire for restraining the sample. Applicant: Hitachi Metals Co., Ltd., Takeana, □'ya...Yukatsu 1 Figure 2 Figure t (C) ζ========; Cliff (”C) Author May Plan Figure

Claims (1)

[Claims] In a Ti-Ni-based shape memory alloy with a Ni-excess composition having two phases: T1Ni phase and T1Ni phase, 50
After solution treatment in a humidity range of 0 to 1100°C, rapid cooling treatment is performed, then aging treatment is performed in a temperature range of 200 to 700°C, cold working is performed to a temperature of 60% or less, and then an additional temperature of 700°C is applied. 1. A method for producing a shape memory alloy, characterized in that memory treatment is performed at a temperature of C or lower.