JPS60243265A - Thin film shape memory alloy - Google Patents

Abstract

PURPOSE:To manufacture the thin film of a shape memory alloy which is difficult to work by forming the thin film of the shape memory alloy on the surface of a substrate with a sputtering method. CONSTITUTION:A shape memory alloy as an Ni-Ti or a Cu-base alloy is poorly workable, and hardly shaped into a thin plate. A substrate made of metals, nonmetals, or organic materials is preheated to >=200 deg.C, and said shape memory alloy is vapor-deposited on the surface by physical or chemical vapor deposition in the form of a thin film consisting of a minute structure and having <=50mum thickness and the grain diameter <=1/3 times the film thickness. In this case, by selecting the conditions that the alloy is quenched and solidified on the substrate, the high-temp. phase is supercooled to room temp. in a noneqilibrium state, and an excellent shape memory alloy in the form of a thin film can be manufactured without requiring heat treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a shape memory alloy, and particularly to a thin film shape memory alloy suitable for fixing onto a substrate from a gas phase and forming it into a thin film.

[Background of the invention]

In the past, shape memory alloys have been put into practical use as relatively large functional materials such as springs, but they have rarely been applied as micro-functional materials related to electronics.

This is because shape memory alloys are difficult-to-process materials and difficult to process into thin plates and the like. Therefore, the shape memory alloy was made into a thin film by sputtering. As a result, it was discovered that thin film shape memory alloys produced under sputtering conditions that satisfy claims 4 to 6 of the present invention exhibit good shape memory effects.

Shape memory alloy effects utilizing the reversibility of martensitic transformation are known in various alloy systems, but practical materials include Ni-Ti and tinol) and Cu-based alloys (e.g.
C, u-Zn-AQ, Cu5n, CuAQ-Ni, etc.) are common.

These alloys are hard in their matrix state and are therefore difficult to process. Therefore, many steps are required to form these into thin plates and the like, resulting in a problem in that the cost of the materials is high. In particular, Cu-based shape memory alloys tend to have coarse grains during processing and heat treatment processes, and furthermore, because they have large elastic anisotropy in the crystal direction, deformation stress concentrates on grain boundaries, making them susceptible to grain boundary fracture. There is a point. Due to the above problems, it is difficult to process shape memory alloys into thin plates.

[Purpose of the invention]

An object of the present invention is to provide a thin film shape memory alloy in which a shape memory alloy is formed into a thin film on a substrate by sputtering, and the thin film shape memory alloy exhibits a good shape memory effect without being heat-treated as in the conventional method. .

[Summary of the invention]

The feature of the present invention is a thin film shape memory alloy that exhibits a good shape memory effect by rapidly cooling and fixing the shape memory alloy onto a substrate (in the same phase) from a gas phase. As the rapid cooling fixation method from the gas phase, there are a physical vapor deposition method and a chemical vapor deposition method.

Specifically, physical vapor deposition methods include general vapor deposition methods, sputtering methods, and ion blating methods. The chemical vapor deposition method is a solidification method using a chemical reaction in a gaseous state. With these methods, the alloy layer solidified on the substrate adheres well to the substrate,
It becomes a good composite material with the substrate. In this case, the substrate may be a metal, a nonmetal, an organic material, or an inorganic material.

Furthermore, the crystal grains in that layer become extremely fine because they are rapidly solidified. Therefore, grain boundary stress concentration due to deformation can be alleviated by making the crystal grains finer, and the ductility of the shape memory alloy, which conventionally had poor ductility due to coarser grains, can be improved. In particular, the particle size is preferably 1/3 or less of the film thickness, and the film thickness is preferably 50 μm or less. This is because when the thickness is 50 μm or more, the grain size increases as the film thickness increases. In addition, conventional shape memory alloys undergo a high temperature solution treatment (approximately 750°C in the case of Cu-AQ-Ni) as a shape memory effect treatment, followed by a melting process to maintain the high-temperature phase at room temperature in a non-equilibrium state. In the present invention, by selecting rapid solidification conditions, the high-temperature phase is appropriately cooled to room temperature in a non-equilibrium state. Therefore, the method of the present invention exhibits a good shape memory effect without requiring a heat treatment step unlike the conventional method. This is very important. In other words, if an organic or inorganic material with relatively low heat resistance is used for the substrate, high-temperature heat treatment for specific solution treatment cannot be performed as in the past (
(This may cause the board to deform). Furthermore, heat treatment causes the crystal grains of the thin film shape memory alloy to become coarse and brittle.

When a shape memory alloy is rapidly solidified on a solid substrate, if the quenching rate exceeds a certain level, the thin film will have a poorly ordered structure even in the amorphous or crystalline phase, and will no longer exhibit the shape memory effect. Therefore, it is preferable to rapidly solidify the film at a rapid cooling rate that is sufficient to regularize the crystal structure of the film. In particular, it is preferable to heat the substrate to be deposited to an appropriate temperature.

[Example of idea]

Example 1 In this example, a Cu-AQ-Ni shape memory alloy was rapidly solidified on various substrates (Cu, Afi, glass, alumina, resin) by sputtering. The composition of the alloy is Cu-1
4%AQ-4%Ni (wt%), oxygen-free steel (J I
SI type), electrolytic Ni (purity 99.5%) and AQ (
(purity 99.8%) was blended and heated in vacuum to 10'-' to 10
A charge of 2.5 kg was subjected to high frequency melting at a temperature of -' Torr. It was cast into an ingot with a diameter of 95 mm. A disk with a diameter of 90 mmφ and a thickness of 5 m+ was cut out by machining from the ingot and used as a sputtering target. A two-pole DC-magnetron type was used as the switching device. The distance between electrodes is 60m, and the inside of the container is 3X10-7T.
After evacuating the film to a vacuum level of 0.05 m, sputter deposition was performed under predetermined manufacturing conditions. As for the thin film production conditions, the sputtering electrode spacing power, substrate temperature, Ar partial pressure during sputtering, and sputtering time were investigated, and the influence of the shape memory effect of the produced thin film shape memory alloy was investigated.

FIG. 1 shows the sputtering time dependence of a sputtered thick film deposited on an AQ substrate (thickness: 20 μm). The shape memory alloy film thickness increases almost linearly with time, and 4
．． It is possible to stack layers up to a thickness of nearly 50 μm in 5 hours. However, although the adhesion to the substrate was good up to 2.0 μm, the adhesion deteriorated as the thickness increased beyond this point, and when the thickness reached 50 μm, it partially peeled off.

In addition, when the sputtered film thickness is 20 μm or less, the crystal grain size is approximately 1 μm.
m or less, but if it becomes thicker than this, the crystal grains become coarse in proportion to the film thickness and become brittle. Therefore, the thickness of the sputtered film is preferably 20 μm or less.

Similar trends were observed on Cu, glass, alumina, and resin plates.

The Cu-14%Aj2-4%Ni shape memory alloy is generated by martensitic reverse transformation of D03 type regular cubic crystals (β phase) existing in the high temperature phase. Therefore, the degree of regularity of the β phase has a strong influence on the shape memory effect, and if the degree of regularity is poor, the shape memory effect will not be exhibited. The second time was Cu-deposited on AQ foil.
The crystal structure of the 14%AQ-4%Ni thin film shape memory alloy is
It was investigated by line diffraction. The sputtering output was 200 W, the sputtering time was 1 h, the substrate temperature was constant at 200° C., and the Ar partial pressure was varied. From the figure, Ar partial pressure is calculated as 4. When increasing from OP a, the regular lattice reflection peak of 311 also appears, and D
The O3 type diffraction pattern becomes clearer. On the other hand, when the Ar partial pressure is lowered, the regular lattice reflection peaks at 111, 200° and 222 become weaker.

The martensitic transformation start temperature (M8) of the Cu-14%AQ-4%Ni shape final alloy is -55°C based on the results of four-terminal electrical resistance measurements. Therefore, as shown in Fig. 2, specimens with a width of 5 mm and a length of 50 m11 were cut out from thin film shape memory alloys with different Ar partial pressures, and their shape memory effects were investigated through the process shown in Fig. 3.

The specimen was bent with a bending radius of 3IIIn so that the shape memory alloy layer side was under tensile stress, and after being eroded into liquid nitrogen to cause plastic deformation, the specimen was returned to room temperature and its shape recovery state was examined. As a result, the Ar partial pressure was 4. Good shape recovery was observed in the specimens of OP a, 8, and OP a.

However, Ar partial pressure 0.7 Pa and 2. No shape recovery was observed in the OP a specimen. As can be determined from the X-ray diffraction results, this is an Ar partial pressure of 0.7 Pa.

2. This is because the crystal structure of OP a has poor regularity in the DO3 type. Similarly, using a Cu foil (thickness: 20 μm) as a substrate, sputtering was performed under the above-mentioned conditions to examine its crystal structure, and almost the same results as in FIG. 2 were obtained.

Similarly, the shape recovery was also the same as the above results.

Using glass, alumina, and resin with a thickness of 0.8 stone as a substrate, X-ray diffraction was performed with four different Ar partial pressures as shown in FIG. 2, and similar results were obtained. In this case, the shape memory effect was determined based on the color of the sputtered film. That is, the shape memory alloy of this composition exhibits a copper color if it is in the β phase, and exhibits a golden color in the case of a poorly ordered β phase or a non-β phase. Ar partial pressure 4, OPa, 8. OPa exhibits a reddish copper color no matter which substrate is used, with a temperature of 0.7 Pa, 2. OP a was golden in color. From the above, the sputtering conditions for obtaining good order of the D03 type regular cubic crystal are Ar partial pressure of 4, OP
a to 8. OP a is preferred.

Example 2 Figure 4 shows an AQ foil substrate with a substrate temperature of 200°C and an Ar
Partial pressure 4. C, u -14%AQ-4%Ni
This is a change in the line diffraction pattern. As shown in FIG. 1, changing the sputtering output greatly changes the film growth rate. However, although there was a slight change in the regular grid reflection pattern of 311 in the X-ray pattern, there was no major change in the overall pattern, and the state of shape recovery was examined using the jig shown in Figure 3 at any sputtering output. Good shape recovery was obtained. Note that similar results were obtained for other substrates.

Example 3 In Figure 5, AQ foil was used for the substrate, and the sputtering output was 2 (J
OW, Ar partial pressure 4. Cu-1,4%AQ-4% sputter-deposited by changing the substrate temperature while keeping OPa constant.
The diffraction peak indicating a change in the X-ray diffraction pattern of Ni shows a typical O3 type pattern when the substrate temperature is 300° C., and as the substrate temperature decreases, the regular lattice reflection peak becomes weaker. When the state of shape recovery was examined using the jig shown in FIG. 3, good shape recovery was observed at substrate temperatures of 200°C and 300°C, but no shape recovery was observed at water cooling temperature (293K) and 100°C. This effect was similar for other substrates. From the above, the substrate temperature should be between 200°C and 300°C.
Good temperature.

(Effects of the Invention) According to the sputtering conditions of the present invention, a good shape memory effect can be obtained by rapidly solidifying the shape memory alloy from the gas phase to the solid phase (substrate) and forming a thin film. Application fields are expected not only as connectors but also as new functional materials (i) by utilizing the color change caused by phase transformation.

,1,′

[Brief explanation of drawings]

Figure 1 shows the Cu layered on AQ foil depending on the sputtering time.
Figure 2 shows the thickness change of 14%Afi-4%Ni shape memory alloy. Figure 2 shows Cu-1 sputter deposited on AQ foil for 1 h by changing the Ar partial pressure while keeping the sputtering power and substrate temperature constant.
Figure 3 shows the X-ray diffraction pattern of the 4%AQ-4%Ni film, Figure 3 shows the method for evaluating the shape memory effect, Figure 4 shows the Af
Cu-14%AQ-4%N was sputter-deposited on i-foil for 1 hour while keeping the substrate temperature and Ar partial pressure constant and varying the sputtering output.
Figure 5 shows the X-ray diffraction pattern of the i-film.
h sputter-deposited Cu-14%AQ-4%Ni film
It is a figure showing a line diffraction pattern. 1... Sputtered film, 2... Substrate, 3... Bending test jig. Agent Patent Attorney Akio Takahashi

Claims (1)

[Claims] 1. A composite material in which a shape memory alloy is fixed to a substrate, wherein the shape memory alloy is appropriately cooled to room temperature in a non-equilibrium state with a high temperature phase, and the high temperature phase changes shape. A thin film shape memory alloy characterized by having a degree of regularity sufficient to exhibit a memory effect. 2. The thin film shape memory alloy according to claim 1, wherein the shape memory alloy is rapidly solidified from a gas phase onto a substrate to form a thin film. 3. The thin film shape memory alloy according to claim 2, wherein the shape memory alloy is formed into a thin film on a substrate by physical or chemical vapor deposition. 4. The thin film shape memory alloy according to claim 1, wherein the substrate is made of an organic or inorganic material. 5. The thin film shape memory alloy according to claim 1, wherein the thin film shape memory alloy has a film thickness of 50 μm or less. 6. The thin film shape memory alloy has a crystal grain size of 17% of the film thickness.
The thin film shape memory alloy according to claim 1, characterized in that the thin film shape memory alloy has a microstructure of 3 or less. 7. The thin film shape memory alloy according to claim 1, wherein the substrate is produced by heating to a temperature at which structural relaxation sufficient to regularize the crystal structure of the shape memory alloy phase occurs. 8. The thin film shape memory alloy according to claim 7, wherein the substrate is heated to a temperature of 200° C. or higher.