JPS6314834A - Tiniv shape memory alloy - Google Patents

Abstract

PURPOSE:To develop a shape memory alloy having a working function at low temp., by subjecting an Ni-Ti alloy composed mainly of specific proportions of Ni and Ti and containing small amounts of V to cold working and then to heat treatment under specific conditions. CONSTITUTION:An ingot of an Ni-Ti-V alloy having a composition in which 0.25-2.0 atomic% V is added and incorporated to an Ni-Ti alloy containing Ni and Ti in an atomic% ratio of 1.02-1.06 is subjected to homogenizing treatment at 900 deg.C for 2hr and is then worked into a fine wire of 1.3mm diameter by means of a hot hammer, hot rolls, and cold wire drawing. The above fine wire is cold-worked to 1.0mm diameter at 40% draft with obviating the necessity of annealing. In this way, the shape memory alloy having remarkable pseudoelastic characteristic at a temp. of ordinary temp. (20 deg.C) or below, particularly at about 0 deg.C, also having a shape memory characteristic of low hysteresis, and increased in utility value for use in refrigerators, medical care, etc., can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to shape memory alloys, particularly shape memory springs and pseudoelastic springs having the function of operating at low temperatures.

(Prior Art) It is well known that TiNi alloys exhibit remarkable shape memory effects and pseudoelastic effects accompanying the reverse transformation of thermoelastic martensitic transformation.

When using T1Ni alloy as a shape memory spring with small hysteresis, it is annealed at 400 to 500°C after cold working.
It is known to utilize intermediate phase transformation by leaving a cold processed structure. A similar method is also used for pseudoelastic springs.

These devices are being put to practical use in home appliance actuators, orthodontic wires, guide wires, brassiere, etc., but all of them are used at temperatures close to body temperature (approximately 35° C.).

(Problem to be solved by the invention) Shape memory alloys are used to
When trying to obtain a spring that operates around 'C, T1
Ni binary alloys require short-time treatment (5-10 minutes) at temperatures of 500-550°C. in this case.

Since the processing time is short, spring back cannot be ignored, and moldability is problematic. Also.

Heat treatment conditions exceeding 500° C. have the disadvantage of increasing hysteresis because the processed structure imparted by cold working disappears.

Also, springs that exhibit pseudoelasticity from around 0°C have a temperature of 400 to 450°C.
Obtained by short-term (5-10 minutes) treatment at <RTIgt;C.

However, like the above, the springback was large and it was difficult to mold the coil bar.

Overcoming these difficulties and making it possible to manufacture elements that operate below room temperature will be extremely important for practical application to actuators for refrigerators, residential ventilation openings, and pseudoelastic springs for automobiles, clothing, medical care, etc. It's important.

The object of the present invention is to provide an actuator spring that operates at temperatures below room temperature (approximately 20'C), particularly around O'C.

and to easily provide a pseudoelastic spring.

(Means and effects for solving the problems) The present invention is characterized in that the atomic percent ratio of Ni and Ti is 1.02 to 1.
．． 06 and 0.25 to 2.0 atomic percent V at 425 to 525 °C after cold working.
By heat treating for 0 to 60 minutes, the operating temperature of the shape memory effect and superelastic effect is shifted to the lower temperature side.

(Example) The present invention will be explained in detail below.

The TiNiV alloy obtained by high-frequency vacuum melting was homogenized at a temperature of 900° C. for 2 hours, and then processed by hot hammering, hot brazing, and cold wire drawing to a diameter of 1.3 RAN. Thereafter, the wire was cold-worked to a diameter of 1.0 g (work rate: 40%) without annealing to obtain a test wire. Table 1 shows the composition of the TiNiV alloy obtained by melting. (The table shows the results of investigation on hot and cold workability.) Table 1 below: 0 Workability Good Δ Poor × Ti4875Ni, one of the obtained alloy wires that cannot be worked
5o7s Vo,s alloy wire (Nn6) at a temperature of 400℃
, 450'C.

and heat treatment was performed at 500° C. for 30 minutes, respectively.

In order to investigate these shape memory properties, temperatures from -20°C to +5°C
A stress vs. strain curve was determined when the temperature was varied up to 0°C. The results at O'C and 20°C are shown in FIG.

For reference, Ti48Ni54 alloy wire at 20'C (
The stress versus strain curve of Nn15) is also shown. These results show that the Ti48y5Ni5075Vos alloy wire exhibits good pseudoelastic properties at 20°C for all heat treatments, and especially for the 400°C and 450°C heat treatments, it exhibits good pseudoelastic properties at 0°C.
However, it can be seen that it exhibits remarkable pseudoelastic properties. On the other hand, the r T' 49 Ni51 alloy wire has difficulty in obtaining pseudoelastic properties at o'c, and cannot obtain pseudoelastic properties at 20°C by heat treatment at 500°C.

FIG. 2 shows the stress versus temperature curve of the alloy wire.
Regarding heat treatment at 400°C and 450°C, the above characteristics are obtained from -10'C.

Next, in order to examine the formability, the 1mmφ wire obtained by cold working was processed into a 6rnMφ coil, heated at 400°C,
Heat treatment was performed at 450°C and 500'C for 30 minutes.

As a result, springs with processed coils (diameter 6 rm) were obtained for the 450'C and 500'C heat-treated materials, but for the 400'C heat-treated material, the coil diameter expanded to 8 rms due to the spring bank. This tendency was also observed in the Ti49Ni51 alloy wire used for comparison. Let's get it again 2. .

The characteristics of the spring showed results similar to those shown in FIG.

The temperature-displacement of a coil spring heat-treated at 500° C. for 30 minutes under constant load was investigated. - As an example, an alloy wire of Nn6 and Nl115 is shown in FIG. (Although the figure shows the displacement due to heating and cooling of the spring under a load of 250g, a stopper is provided to prevent the displacement of the spring in a low temperature range.) From this result, it is clear that the coil spring of the alloy (lI & 16) according to the present invention The martensitic transformation start temperature (Mg point) and reverse transformation completion temperature (Af point) were 4°C and 7°C, respectively. On the other hand, Ti4 as a comparison
The Ms point and Af point of the 9Ni alloy (Nn15) coil spring were 26°C and 35°C, respectively. In other words, the alloy according to the present invention exhibits transformation temperature hysteresis (Af-Ms
) and two low operating temperatures (Mar and Af).

FIG. 4 shows the results of examining the transformation temperatures of the alloys listed in Table 1, which were heat-treated at 750° C. for 1 hour.

In the figure, (1) is V in the form 'rt49Ni 51-x''x.
Relationship between the Ms point and the amount added (x) when added.

(2) is Ti49-X Nis+VX, (3
) shows the respective relationships when added in the form of T' 49-x/2 Ni51-x//2vx.

As a result, as the amount of addition increases, the Ms point decreases for all addition systems. From this, it is expected to add a large amount of ■ to produce a low transformation point material, but the cold workability worsens as the amount added increases, and as shown in the table, in particular, when the amount exceeds 2 at%, almost no It could not be processed.

On the other hand, no effect was observed when the amount added was less than 0.25 at%. The reason for limiting the alloy composition is that the atomic percent ratio of Ni and Ti is less than 1.02.1 For example, Ti495N
With alloy compositions such as i495V10 Ti495Ni50VO5, it is difficult to recognize the significant effect of lowering the transformation temperature. Further, the atomic percentage ratio exceeds 1.06.

For example, Ti47.5 Ni52 Vo,s, Ti
With alloy compositions such as 47,75 Nis+, 7s Vo, and s, although a remarkable decrease in transformation temperature is observed, processing is hardly possible. The optimum range of V addition in the present invention is 0.5 to 1.
In addition, the Ni concentration of the master alloy (TiNi alloy) used for addition is 50 to 51, which exhibits good shape memory properties.
It is at%.

(Effects of the Invention) As explained above, the shape memory alloy according to the present invention exhibits remarkable pseudoelastic properties at room temperature (approximately 20° C.) or lower, particularly at around 0° C.

It has the effect of exhibiting shape memory characteristics with low hysteresis, and can be expected to be applied to refrigerators, medical care, and clothing.

[Brief explanation of drawings]

Figure 1 shows the alloy NcL6 (Ti4875 N
i so 75vo, s alloy), Nn15 (Ti4
9Ni51 alloy) at 500'C. O'Cl after treatment at 450°C and 400°C
Stress vs. strain diagram at 20°C. Figure 2 shows the relationship between yield stress and temperature for the alloy Nn 6'k 500.450.400'C in Figure 1, which was heat treated for 500.450.400'C. (The solid line indicates the temperature range of pseudoelastic characteristics.) Figure 3 shows two coil springs made of strands of alloy 6 and Nn6, which were formed into coil springs by heat treatment at 500°C.
A diagram showing the relationship between temperature and displacement under a load of 50 gr (coil diameter: 6.0 + + mφ, wire diameter 1.0), Figure 4 shows the Ms of the alloy used in this test after being heat treated at 750 ° C for 1 hour. A diagram showing the relationship between points and V addition amount (in the diagram, ■ ~ [phase]
is the alloy number in the text table, (1) is Ti49Ni51-x
VX, f2) is Ti 49-xNi 51. , Vx
, (3) is Ti49-X/2" 51-x/2
This shows a vx addition system. ). Figure 3 Figure 4

Claims (2)

[Claims] (1) The atomic percent ratio of Ni and Ti is 1.02~
A shape memory TiNiV alloy comprising a TiNiV alloy containing 1.06 and 0.25 to 2.0 atomic percent V. (2) Shape memory T according to claim 1, which is obtained by heat treatment at 425 to 525°C for 10 to 60 minutes after cold working.
iNiV alloy.