JPH07252553A - Method for melting and casting ni-ti-nb based shape memory alloy - Google Patents

Abstract

PURPOSE:To reduce the variation in the composition of an Ni-Ti-Nb shape memory alloy and to reduce the variation in the transformation temp. Ms of gold. CONSTITUTION:An Ni-Ti-Nb alloy having a composition in the area enclosed by point A of, by atom, 47.0% Ni, 50.0% Ti and 3.0% Nb, point B of 50.0% Ni, 47.O% Ti and 3.0% Nb, point C of 46.O% Ni, 40.0% Ti and 14.0% Nb and point D of 40.0% Ni, 46.0% Ti and 14.0% Nb in the ternary alloy constitutional diagram is melted and cast. In this case, the raw materials of Ni, Ti and Nb are mixed to attain the composition, and the mixture is melted and cast by high-frequency induction heating in vacuum or in an inert atmosphere. Consequently, a stabilized Ni-Ti-Nb based shape memory alloy is melted and cast.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for melting and casting a Ni-Ti-Nb type shape memory alloy with little variation in composition components.

[0002]

2. Description of the Related Art A Ni-Ti alloy having an atomic ratio of about 1: 1 has a cubic crystal structure of a high temperature phase (hereinafter referred to as a mother phase), and when cooled, it transforms at a martensitic transformation temperature to form a monoclinic crystal. The structure becomes a martensite phase (hereinafter, M phase). Along with this, excellent characteristics such as a shape memory effect and a superelastic phenomenon are exhibited. Therefore, the transformation temperature is important in controlling the properties of the shape memory alloy. The transformation temperatures of the shape memory alloy are Ms and Mf points at which the transformation from the parent phase to the M phase starts and ends, respectively, and As and Af at which the transformation from the M phase to the parent phase begins and ends. Call it a point. These transformation points of transformation reverse transformation have a gap, which is called temperature hysteresis. Reference 1 (M
RS. Proc., Vol. 246, 1992).
The temperature hysteresis of the Ti2 alloy is 20 to 40 ° C, whereas the Ni-Ti-Nb alloy has a considerably wide range of 60 to 100 ° C. Taking advantage of this feature, it has been put to practical use as a pipe joint that heats and shrinks.

A conventional shape memory pipe joint is made of an alloy having a low transformation temperature (about -100 ° C.), the diameter of the joint is expanded, and the joint is stored in liquid nitrogen. I was waiting for you to rise. On the other hand, Ni-Ti-N
The heat-shrink type pipe joint using the b alloy is in a state where the diameter is expanded at room temperature and heats to shrink the pipe. Since there is no need to use liquid nitrogen, the construction is much easier. However, the reference (MRS.Proc., Vol.
As described in 9), the melting point of Nb in the Ni-Ti-Nb alloy is high, and there is a problem that it cannot be melted without electron beam melting. Further, the ingots obtained by electron beam melting have a large variation in composition, and as a result, the transformation temperature, which is the most important for shape memory alloys, varies.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made as a result of studying the above-mentioned problems, and there is little variation in the components of Ni-Ti-Nb alloy, and as a result, variation in transformation temperature, which is important as a shape memory alloy, is reduced. This is the development of a melting and casting method that produces less alloy.

[0005]

SUMMARY OF THE INVENTION The present invention provides a Ni-Ti and Nb ternary alloy phase diagram for A, B, C and D.
The composition of the points indicated by is atomic% A: Ni 47.0%, Ti 50.0%, Nb 3.0
% B: Ni 50.0%, Ti 47.0%, Nb 3.0
% C: Ni 46.0%, Ti 40.0%, Nb 14.
0% D: Ni 40.0%, Ti 46.0%, Nb 14.
In melt casting of a Ni-Ti-Nb alloy having a composition within a region surrounded by 0%, Ni raw material, Ti raw material, and Nb raw material are blended so as to have the above composition, and are mixed in a vacuum or by vacuum induction heating. A method of melting and casting a Ni-Ti-Nb-based shape memory alloy, which comprises melting and casting in an inert atmosphere, according to claim 1, wherein the Ni raw material is placed in a lower portion of the crucible and melted. And Ni according to claim 1.
A method for melting and casting a -Ti-Nb-based shape memory alloy.
The Ni-Ti- according to claim 1 or 2, wherein the alloy is melted using a carbon crucible.
A method of melting and casting an Nb-based shape memory alloy is defined as claim 3.

[0006]

In the present invention, the composition of the target alloy is limited as described above, because outside this range, the shape memory characteristics are not appropriate, or the workability is deteriorated and the alloy cannot be practically manufactured. Is. Further, the reason for melting by high-frequency induction heating is to stir the molten metal by the stirring action by high-frequency waves so that there is no variation in the components. desirable. Further, the reason why the melt casting is performed in a vacuum or in an inert atmosphere is to prevent the oxidation of Ti, which is a very active metal.

The metallic Ni as a raw material is set in the lower part of the crucible so that Ni having a low melting point is first melted and the reaction heat at the time when Ti is melted causes the Ni to melt at once, so that there is little variation in composition. . Further, the reason why the carbon crucible is used for melting the alloy is that the Ni-Ti melt is less corroded and the impurities are less mixed. The Ni-Ti-Nb type shape memory alloy in the present invention also includes a superelastic alloy having the same composition as described above.

[0008]

EXAMPLES An example of the present invention will be described below.
For alloys having the composition shown in Table 1, the raw materials were weighed and
Using a carbon crucible with a high frequency induction heating furnace of 0 KHz, a Ni raw material is placed in the lower portion, and a Ti raw material, N
b Place the raw material, dissolve in an argon atmosphere, and
It was cast in a copper mold of cm. For comparison, melting was also performed with an electron beam, and a similar mold was cast.
From the bottom of the mold, sample 20mg of the alloy from 1,3,5,7,9,11,13cm position and place it in vacuum at 950
After carrying out solution treatment at 1 ° C. for 1 hour, the transformation temperature was measured by a differential scanning calorimeter (DSC). The results are shown in Table 2.

[0009]

[Table 1]

[0010]

[Table 2]

As is clear from Table 2, both alloy A and alloy B produced by the method of the present invention have significantly less variation in the transformation temperature Ms point.

[0012]

As described above, according to the present invention,
In the melt-casting method of Ni-Ti-Nb alloy, it is possible to obtain stable industrial shape memory characteristics with less variation in transformation temperature, and to promote the practical application of shape memory alloys.

[Brief description of drawings]

FIG. 1 is a phase diagram of a Ni—Ti—Nb ternary alloy which is a target of the present invention.

Claims (3)

[Claims] 1. In a ternary alloy phase diagram of Ni—Ti and Nb, the composition of points indicated by A, BC and D is atomic%.
Then, A: Ni 47.0%, Ti 50.0%, Nb 3.0
% B: Ni 50.0%, Ti 47.0%, Nb 3.0
% C: Ni 46.0%, Ti 40.0%, Nb 14.
0% D: Ni 40.0%, Ti 46.0%, Nb 14.
In melt casting of a Ni-Ti-Nb alloy having a composition within a region surrounded by 0%, Ni raw material, Ti raw material, and Nb raw material are blended so as to have the above composition, and are mixed in a vacuum or by vacuum induction heating. A method of melting and casting a Ni-Ti-Nb-based shape memory alloy, characterized by performing melting and casting in an inert atmosphere. 2. The Ni—Ti according to claim 1, wherein the Ni raw material is placed in a lower portion of the crucible and melted.
-A method for melting and casting Nb-based shape memory alloy. 3. The Ni according to claim 1, wherein the alloy is melted by using a carbon crucible.
A method for melting and casting a Ti-Nb-based shape memory alloy.