JPS63227754A - Formation of niti shape memory alloy - Google Patents

Abstract

PURPOSE:To easily form the titled alloy into the shape and dimensions at the time of assembly, by carrying out the deformed-shape constraint and subsequent constraint removal of the titled shape-memory-treated alloy at respectively specified temps. and forming the alloy into the required shape. CONSTITUTION:A shape memory alloy (NT alloy) composed principally of intermetallic compound NiTi is melted, cast, and then subjected to hot and cold rollings so as to be formed into a tape shape. This NT-alloy bar is formed by roll forming into a U shape having a further opened end and then subjected to shape memory treatment in the above state. Subsequently, this alloy 1 is subjected to deformation constraint at a temp. where an austenitic phase starts developing or above by means of jigs 2a, 2b constraining so that two open ends of the U shape are closed. Then, after the NT alloy 1 is cooled together with the jigs 2a, 2b down to a temp. where an R or martensitic phase starts developing or below, the jigs 2a, 2b are demounted and constraint is removed. By this method, the NT alloy 1 is free from shape recovery due to spring back and maintains the constrained shape.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a method for forming a Nil'-i-based shape memory alloy (hereinafter abbreviated as NT gold alloy) into a shape necessary for assembling it in a predetermined location of a certain part. It is about the method.

[Conventional technology]

NT gold alloy is an intermetallic compound NiTi containing Ni and 1'-t in an atomic ratio of 1:1, or either one or both of Ni and Ti is combined with a trace amount of an element such as Fe, Cr, CO.
It is an alloy substituted with, etc., and has a shape memory effect, a superelastic effect, and a transport prevention effect. The shape memory effect caused by thermoelastic martensitic transformation occurs at the temperature at which the NT gold alloy begins to transform into the martensitic phase (hereinafter abbreviated as the MS point) or at the R phase that exists between the austenite phase and the martensitic phase, which are the parent phases. The deformation applied to the NT alloy at a temperature below the temperature at which transformation begins (hereinafter abbreviated as the M2S point) undergoes reverse transformation to the austenite phase at a certain temperature (hereinafter abbreviated as the AS point) due to heating, and the shape is memorized in the austenite phase in advance. This is a phenomenon of restoration. In addition, regarding the superelastic effect and vibration damping effect caused by stress-induced martensitic transformation in the matrix, the former is caused by applying stress and giving a strain of several percent, causing martensitic transformation, and unloading it to reverse the effect. This refers to a phenomenon in which the shape is completely restored through transformation, and the latter refers to a phenomenon in which vibration energy from the outside is absorbed and vibrations are quickly attenuated by the hysteresis of the stress-strain curve that occurs along with the superelastic effect.

This effect is not limited to NT alloys but also AuCd.

Although it has also been found in CuZnA1 alloys, etc., NT alloys are the most superior in terms of properties and workability, and various uses have been considered for actuators, fasteners, springs, etc., and in some cases they have been put into practical use. has been done. Furthermore, recently, the fields of application of NT alloys have expanded considerably, and their uses have become more and more complex, and active attempts have been made to apply them to small parts such as electronic parts.

Examples include fasteners as reinforcing members for joining FPCs and glass substrates, zero force insertion connectors, and the like.

In order to perform shape memory treatment on the NT alloy used as an element to be assembled into these small parts, a method is used in which the NT alloy is molded into a certain shape by a warm forming method or the like. On the other hand, in order to assemble the NT alloy element into a small part, the shape memory treated alloy must be deformed into a predetermined shape and then assembled. However, since NT alloys have a wider elastic range than ordinary metals,
Particularly in the austenite phase, even if it is deformed into a predetermined shape, it will return to its original shape when the restraining force is removed. That is, as shown in Fig. 1, an NT alloy (1) is formed by forming a tape-like strip into a U-shape with one end further open and subjected to shape memory treatment.
In order to obtain the U-shaped open end of the alloy as shown in Fig. 3, the two tips of the open end of the 0-shape are closed as shown in Fig. 2. Jig (2
a) If (2b) is removed, the NT alloy (1) will almost return to its pre-deformation shape as shown in FIG. 4, making it impossible to obtain a shape suitable for assembly.

Therefore, in the current assembly, the NT alloy is deformed by cooling it to the R phase or martensitic phase region. It is done using.

[Problem that the invention seeks to solve]

However, even in such an R phase or martensitic phase, the NT alloy cannot completely obtain a predetermined shape due to the springback of the elastic deformation valve. That is, a jig (2a) is used to restrain the U-shaped NT alloy (1) that has been subjected to shape memory treatment as shown in FIG. After deforming the jig (2b) at a temperature below the MS point, the jig (2a) is deformed at the same temperature.
If (2b) is removed, the open end of the 0 character of the NT alloy (1) will not be completely closed and will always open due to springback, as shown in Figure 5, and the NT alloy will not be assembled into other parts. It has been difficult to obtain the desired shape unless more deformation is applied than necessary to obtain the desired shape.

[Means for solving problems]

In view of this, the present invention has made the following findings as a result of various studies.

After melting and casting a 50.6at%N 1-49.4at%Ti alloy according to a conventional method, the NT alloy strip was processed into a tape shape by hot rolling and cold rolling, and the NT alloy strip was formed into a tape shape by roll forming as shown in Fig. 6 (a). As shown in the figure, the two ends of the open end of a U-shape were formed into a closed shape in which they were in contact with each other, and shape memory treatment was performed in this shape. Note that the completion temperature of the reverse transformation from the martensite phase to the austenite phase of this NiTi alloy (hereinafter abbreviated as Af point) is 30° C., and at temperatures above the Af point, the alloy is entirely in the austenite phase. As shown in FIG. 6 (b), the tensile test jigs (4a) (4b) are sandwiched between the contacting tips of the NT alloy (3), and the NT gold alloy 3 is pulled with a load (W) in opposite directions. ) was measured to measure the fitting pressure of the NT gold alloy having such a shape. The results are shown in FIG. 7 as a relationship between tensile load (W) and displacement <i>. The curve (A) in the figure shows the NT gold alloy 3) shown in Figure 6 (a) at -6
The results are shown in Figure 6 (b), where the tensile test jig (4a) (4i)) was inserted at a temperature of 0°C, and then the tensile test was carried out after raising the temperature to -30'C. , curve (B
) is -60% of the NT gold alloy 3) shown in Figure 6 (a).
At a temperature of ℃, the tensile test jig (
4a) After sandwiching (4b), the whole was heated to 40°C, then cooled to -30'C, and then subjected to a tensile test. As can be seen from this figure, the rise of the initial tensile load, that is, the mating force, is significantly different between curve (A) and curve (B), and curve (13)
In curve (A), almost no fitting force is generated, whereas in curve (A), fitting force is clearly generated.

This indicates that if the N-type alloy is cooled to the martensitic phase while its shape is restrained by the austenite phase, the shape at the time of restraint will be maintained even if the restraint is released. Based on the above knowledge and as a result of further studies, we have developed a method that allows NT gold alloy to be formed into a desired shape.

That is, one aspect of the present invention is to apply shape memory treatment to a shape memory alloy containing the intermetallic compound Nil'-i as a main component, and then deform the alloy at a temperature higher than the temperature at which the austenite phase begins to be generated to restrain the shape. Then, the above-mentioned restriction is released by cooling to a temperature below which the R phase or martensitic phase starts to be generated, and the product is molded into a desired shape.

Another aspect of the present invention is to perform shape memory treatment on a shape memory alloy containing the intermetallic compound NiTi as a main component, and then deform the alloy at a temperature below the temperature at which R phase or martensitic phase begins to occur. is restrained, heated above a temperature at which an austenite phase begins to occur, and then cooled down to a temperature at which an R phase or a martensitic phase begins to be generated to release the above restraint and form it into a desired shape. It is something to do.

[For production]

NT gold alloy MS is deformed into the desired shape above the As point.
Even if the shape restraining force is released by cooling below the M'S point or the M'S point, springback hardly occurs in the alloy. This is because site metamorphosis occurs, and therefore, even if the restraining force is released, no force is generated to restore the shape to its original shape.

In addition, it is the martensitic phase region or R that is first deformed at a temperature below the Ms point or MZs point to restrict its shape, then heated above the AS point, and then cooled again below the MS point or MZs point. This is because the phase region has a smaller elastic modulus than the austenite phase region and requires less force for deformation, and therefore can be deformed into a desired shape with a small force below the MS point or M'S point.

(Example〕 Examples of the present invention will be described below.

Example (I) After melting and casting a 50.68°C% N 1-49.4at% l-i alloy according to a conventional method, the NT alloy strip was processed into a tape shape by hot rolling and cold rolling, and then roll forming. As shown in FIG. 1, it was molded into a U-shape with one end roughly open, and shape memory treatment was performed in this shape. Note that the Af point of this alloy (1) is 30°C. The alloy (1) is 4
A jig (2a) that restrains the two ends of the open end of the U-shape as shown in Figure 2 at a temperature of 0°C (
The deformation was restrained in 2b). Next, the jig (2a) (2b
) and the NT gold alloy 1) were cooled to -60°C, and the restraint jigs (2a) and (2b) were removed.
) maintained its restrained shape as shown in Figure 3, and there was no recovery of the shape due to springback.

Example (II) In addition, the NT gold alloy 1) subjected to the above shape memory treatment was
The restraining jig (2a) shown in Fig. 2 in a state cooled to 0°C (
After deforming and restraining in step 2b), the N-type alloy (1) was heated to 40°C together with the jigs (2a and 2b), cooled again to -60°C, and the restraint holders (2a and 2b) were removed. However, the NT alloy (1) maintained its constricted shape as shown in FIG. In this case, the binding force at -60°C was roughly less than half of the binding force at 40°C in Example (I).

(Effects of the Invention) As described above, according to the present invention, the shape and dimensions can be easily formed when assembling the NT alloy as a component, and other industrially significant effects are achieved.

[Brief explanation of the drawing]

Figure 1 is a side view of the NT alloy before deformation, and Figure 2 is a side view of the NT alloy before deformation.
FIG. 3 is a side view showing the state in which the alloy is deformed and restrained. FIG. 3 is a side view showing the NT alloy after the restraining force is released according to the embodiment of the present invention. FIGS. A side view showing the alloy, Figures 6 (a) and (b) show the method for measuring the fitting pressure, (a) is a side view showing the NT alloy before measurement, and (b) shows the tension jig. The attached side view and FIG. 7 show the results of a fitting pressure test, and are actual measurement diagrams showing the relationship between tensile load and displacement. 1...NT alloys 2a, 2b for forming tests
...Deformation restraint jig 3...NT gold alloy a, 4b for fitting pressure measurement
...Tensile test jig A...Load measured after being restrained in the martensite phase-displacement curve B...Load measured after being restrained in the austenite phase- Displacement curve each W → 1 [ 1 fold (, e)

Claims (2)

[Claims] (1) After shape memory treatment is applied to a shape memory alloy containing the intermetallic compound NiTi as a main component, the alloy is deformed at a temperature higher than the temperature at which austenite phase begins to be generated to restrict its shape, and then R phase or martenite phase is formed. A method for forming a NiTi-based shape memory alloy, which comprises cooling the NiTi-based shape memory alloy to a temperature below the temperature at which a site phase begins to release the above-mentioned constraint, and forming the NiTi-based shape memory alloy into a desired shape. (2) After applying shape memory treatment to a shape memory alloy containing the intermetallic compound NiTi as a main component, the alloy is deformed at a temperature below the temperature at which R phase or martensitic phase begins to be generated to restrain its shape, and then NiTi-based shape memory characterized by heating above a temperature at which an austenite phase begins to occur, and then cooling below a temperature at which an R phase or a martensitic phase begins to release the above constraints and forming into a desired shape. How to form alloys.