JPH0539554A - Manufacture of shape memory alloy - Google Patents

Abstract

PURPOSE:To provide a shape memory allay small in settling at the time of repeatedly executing heating and cooling. CONSTITUTION:Alloy stock constituted of, by atom, 40 to 50% Ni, 5 to 12% Cu and the balance Ti is subjected to cold working at 10 to 30% draft and is thereafter subjected to shape memorizing treatment under the conditions, at 350 to 550 deg.C for to 120min.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a shape memory alloy.

[0002]

BACKGROUND OF THE INVENTION Shape memory alloys, even when deformed at low temperature (martensite phase state), restore their shape to a previously stored shape when heated to a predetermined temperature. And is used in various fields.

As one of its utilization forms, this is formed into a coil-shaped spring and is combined with a bias spring (normal spring) to form a bidirectional shape memory element, which can be repeatedly used. It is used as.

For example, a coil spring of a shape memory alloy and a bias spring are combined and set in a direction in which they press each other, and the spring of the shape memory alloy is bent by the spring force of the bias spring in the low temperature state, while it is set in the high temperature side. The coil spring of shape memory alloy is restored to the memory shape while deforming the bias spring.

This utilizes the characteristic that the shape memory alloy recovers its shape at a predetermined temperature and, at the same time, has a large recovery force.

By the way, shape memory alloys having various compositions are known at present, and one of them is a composition obtained by adding Cu as a third element to a NiTi alloy.

In NiTi alloys, the transformation temperature greatly decreases as the Ni concentration increases, and it is customary that the transformation temperature also significantly decreases by the addition of a third element such as Fe, Co, Cr. It is known that when Ni in the NiTi alloy having an atomic ratio is replaced with Cu, it can be replaced up to ten percent, and the transformation temperature does not decrease, but rather tends to increase.

Further, it is known that the mechanical properties are significantly changed by Cu substitution. For example, with 10% substitution, the yield stress of the martensite phase becomes extremely small,
On the contrary, in the matrix phase, it becomes larger than that of the NiTi alloy.

By the way, when the coil spring as described above is formed by using the shape memory alloy composed of Ni-Ti-Cu and is used as an actuator for various purposes, the deformation-shape recovery due to temperature change is repeated. In addition, there is a problem that the shape recovery power gradually decreases and a so-called sag phenomenon occurs.

When such a sag appears largely, the function as an actuator or the like is deteriorated, or there is a problem that the actuator does not operate as set.

[0011]

The present invention has been made in order to solve the above problems, and the gist thereof is the atomic ratio of Ni: 40-50%, Cu: 5-12%, balance Ti. After cold working the material alloy consisting of 10 to 30% at a working rate, a memory treatment is performed under the conditions of 350 to 550 ° C. and 20 to 120 minutes.

As described above, the present invention is characterized in that the cold working rate and the memory processing condition are set to predetermined conditions, whereby the above deformation-shape recovery (heat cycle) is repeated in the use state. In this case, the effect of reducing the settling can be obtained.

When the shape memory alloy is formed as a coil spring as described above, for example, the coil spring is liable to be sagging when subjected to a thermal cycle, because dislocations and other defects are caused in the tissue during use. It is thought that the cause is appearance.

On the other hand, when cold working is performed to form such a coil spring from the material alloy, defects such as dislocations similarly occur.

Therefore, in the present invention, defects such as dislocations that should appear during use are made to appear in advance, and an appropriate processing rate for this purpose is determined, and this is determined within the range of 10 to 30%. Is.

When the material alloy is processed under such conditions, defects that should appear are revealed in advance. Therefore, when this is formed into a coil spring and used, for example, and repeatedly subjected to thermal cycles, the initial state The amount of settling is relatively small, and the initial shape recovery force is maintained well.

In the present invention, in addition to the above cold working rate, the memory processing temperature is regulated to 350 to 550 ° C.

In the Ni-Ti-Cu alloy, the conventional memory treatment is usually performed at a high temperature of 550 ° C to 750 ° C.

However, according to the research conducted by the present inventor, it was found that the treatment temperature in the memory treatment of the Ni-Ti-Cu alloy had a great influence on the above-mentioned settling, and therefore an appropriate treatment temperature was found. However, it has been found that it is preferable to carry out at a temperature lower than that conventionally carried out, specifically at a temperature of 550 ° C. or lower.

However, when the memory processing is performed at a temperature lower than 350 ° C., the memory processing becomes insufficient and springback is likely to occur. Therefore, in the present invention, the lower limit of the processing temperature is 350 ° C.

On the other hand, regarding the processing time, this is 20 to 1
It is necessary to set the range to 20 minutes. If it is longer than 120 minutes, the effect of suppressing fatigue will be insufficient, and conversely 2
If the time is shorter than 0 minutes, sufficient storage processing cannot be performed.

[0022]

EXAMPLES In order to further clarify the characteristics of the present invention, examples thereof will be described in detail below. Ni: 42.8 by atomic ratio
%, Ti: 50.2%, Cu: 7.0% alloy was melted, forged and rolled, and then cold drawn at a working rate of 30% to obtain a wire having a wire diameter of 1.0 mmφ.

Next, from this wire, the winding diameter is 9.0 mm and the number of windings is 5
Once, a coil spring having a coil pitch of 4.0 mm and a height of 22 mm was manufactured, and then a memory process was performed in a shape-restricted state. The memory treatment was performed under the condition of 400 ° C. × 30 minutes.

Next, while the coil spring was kept in a constant strain state (spring height 10 mm), a heat cycle of 20 ° C. to 90 ° C. was applied to measure the shape recovery force. The heat cycle was applied at 20 ° C. and 90 ° C. for 1 minute each.

In addition, the same test was conducted by changing the treatment temperature variously and the shape recovery force was measured. The results are shown in FIGS. 1, 2 and 3.

FIG. 1 shows the shape recovery force after the heat cycle was applied 1000 times and 5000 times when the memory treatment was carried out under the condition of 400 ° C. × 30 minutes and the heat recovery was applied 1000 times and 5000 times. It is shown by taking the generated force (shape recovery force) on the shaft.

FIG. 2 is a diagram corresponding to FIG. 1 when the storage process is performed under the condition of 700 ° C. × 30 minutes.

On the other hand, FIG. 3 shows the effect of the heat treatment temperature on the relationship between the heat cycle and the shape recovery force. The number of heat cycles is plotted along the horizontal axis and the heat cycle is plotted along the vertical axis. The force (shape recovery force) is shown as a ratio to the generated force in the initial state.

From the above results, particularly from the results of FIG. 3, those employing the storage processing temperatures of 400 ° C. and 500 ° C., which are within the range of the present invention, have less settling, while the processing temperatures of 600 ° C. and 700 ° C. It can be seen that the ones that adopted are large in settling and tend to be unstable.

Regarding the products which were stored at a temperature lower than 350 ° C., the storage process was insufficient and good results were not obtained.

[Example 2] Ni: 40.6 in atomic ratio
%, Cu: 10.0%, the balance Ti is melted, forged and rolled, and then the working ratio is 5%, 11.7%, 20.
% And 28% were cold drawn to obtain a wire having a wire diameter of 1.0 mmφ.

Next, from this wire, the winding diameter is 9.0 mm and the number of windings is 5
Once, a coil spring having a coil pitch of 4.0 mm and a height of 22 mm was manufactured, and then a memory process was performed in a shape-restricted state. The memory treatment was performed under the condition of 400 ° C. × 30 minutes.

Next, a thermal cycle of 20 ° C. to 90 ° C. was applied up to 5000 times while maintaining the coil spring in a constant strain state (spring height 10 mm). The heat cycle here is 20
C. and 90.degree. C. were added under the condition of holding for 1 minute each.

Then, based on the shape recovery force without heat cycle, the heat cycle is repeated 1000 times, 5000 times.
When the relative recovery force after the addition was calculated, it was as shown in FIG. In the figure, the horizontal axis represents the cold working rate and the vertical axis represents the relative recovery force.

From the results shown in FIG. 4, it can be seen that the relative recovery force is remarkably low when processing is performed at a processing rate of less than 10%.
When the processing rate was over 30%, cracking occurred and the product was not produced.

From the above, it can be seen that a suitable processing rate is 10 to 30%.

[Example 3] Ni: 39.4 in atomic ratio
%, Cu: 11.0%, the balance Ti was melted, forged, rolled, and then cold drawn at a working rate of 20% to obtain a wire rod having a wire diameter of 1.0 mmφ.

Next, from this wire, the winding diameter is 9.0 mm and the winding number is 5
Once, a coil spring having a coil pitch of 4.0 mm and a height of 22 mm was manufactured, and then a memory process was performed in a shape-restricted state. Memory processing is 400 ℃ x 15 minutes, 30 minutes, 60 minutes, 90 minutes, 1
20 minutes, 142 minutes and 500 ° C x 15 minutes, 30 minutes, 60
Min, 90 minutes, 120 minutes, 142 minutes.

Next, a thermal cycle of 20 ° C. to 90 ° C. was applied up to 5000 times while maintaining the coil spring in a constant strain state (spring height 10 mm). Here, the thermal cycle is 20 ℃,
They were added at 90 ° C. for 1 minute each.

Then, the shape recovery force after the heat cycle was measured, and the relative recovery force after the heat cycle was applied 5000 times was calculated based on the shape recovery force in the state where the heat cycle was not applied. It was the street. In FIG. 5, the horizontal axis represents the storage processing time and the vertical axis represents the relative recovery force.

From the results of FIG. 5, it can be seen that the relative recovery power is remarkably low when the processing time is less than 20 minutes or more than 120 minutes regardless of whether the temperature is 400 ° C. or 500 ° C.

The embodiment of the present invention has been described in detail above, but this is merely an example, and the present invention can be applied to the production of a leaf spring or other member made of a shape memory alloy. It can be implemented in a mode in which various changes are made based on the knowledge of those skilled in the art without departing from the scope.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a temperature before and after a thermal cycle and a generated force (shape recovery force) obtained in an example of the present invention.

FIG. 2 is a diagram corresponding to FIG. 1 when a storage process is performed under a condition different from that of FIG.

FIG. 3 is a diagram showing a decreasing tendency of a generated force (shape recovery force) when a heat cycle is applied.

FIG. 4 is a diagram showing the relationship between the cold workability and the relative recovery force obtained in the example of the present invention.

FIG. 5 is a diagram showing the relationship between the storage processing time and the relative recovery force obtained in the example of the present invention.

Claims (1)

[Claims] 1. Atomic ratio of Ni: 40 to 50%, Cu:
Material alloy consisting of 5-12% and balance Ti 10-
After cold working at 30%, 350-550 ° C, 20-1
A method for producing a shape memory alloy, characterized by performing a memory treatment under a condition of 20 minutes.