JPH1046208A - Production of ti-ni base alloy sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the regulation of the compsn. in a sintered body and to furthermore attain the uniformization of the compsn. and the improvement of the sintered density, at the time of producing a Ti-Ni base alloy sintered body, by mixing Ti and Ni raw material powder and subjecting it to discharge plasma sintering. SOLUTION: Ti powder produced by an atomizing process and Ni powder produced by a carbonyl process are mixed. While it is compacted under about 20MPa in a vacuum, discharge plasma sintering is executed. In this way, the realative density of the sintered body can be regulated to about ±95% in the case of a powdery mixture with an atomic weight ratio of 50; 50. More preferably, the powdery mixture is mechanically alloyed in an atmosphere of an argon gas, is thereafter filled into a mold made of carbon for sintering and is subjected to discharge plasma sintering. Thus, the intrusion of oxygen can be suppressed, and moreover, the relative density can be increased to about 98%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a TiNi-based alloy sintered body that is a shape memory and superelastic material.

[0002]

2. Description of the Related Art Until now, the mainstream of TiNi-based alloy production has been the melting casting method, but since it always goes through a melting step,
It is well known that the uniformity of the composition for each production lot and within the production lot is poor.

[0003] In practice, in the case of shape memory alloys and superelastic alloys that are widely used as functional materials among TiNi-based alloys, control of the transformation temperature is particularly important as a function. Although the Ni composition fluctuates by 0.1%, the transformation temperature in that case also fluctuates by about 10 ° C.

From an industrial point of view, the transformation temperature, that is, the temperature at which the shape recovers, is desired to be suppressed to about ± 2 ° C.

Therefore, in order to improve the poor controllability of the composition by the melt casting method, a mixed powder obtained by mixing a Ti powder and a Ni powder by a powder mixing method, which is a kind of powder metallurgy, is pressed. Production of a TiNi-based shape memory alloy by sintering is being studied.

[0006] For example, in the case of a product having a complicated shape such as a tube, the study of the production by the powder metallurgy method is very industrial, and various studies have been made at present.

[0007] Such a complicated shape cannot be formed by the melting and casting method, which has been the mainstream of the production of TiNi-based alloys, and thus the necessity has been further increased.

[0008]

However, when actually examined, no TiNi sintered body having a relative density exceeding 90% has been obtained.

It is considered that the cause is that pores are easily generated due to the difference in the mutual diffusion coefficient between Ti and Ni.

Therefore, the technical problem of the present invention is that the relative density of a sintered body manufactured by the TiNi-based alloy powder mixing method is 90%.
% Of technical shortcomings such as less than 9%
It is an object of the present invention to provide a method for producing a TiNi sintered body capable of obtaining a relative density exceeding 0%.

[0011]

A dense TiNi alloy sintered body can be obtained by subjecting a mixed powder obtained by mixing a Ti powder and a Ni powder to spark plasma sintering, which is a kind of pressure sintering.

In the spark plasma sintering, a powder is filled in a carbon mold and pressure sintering is performed. An electric current is directly applied to the carbon mold to heat the powder using carbon as a heating element. Therefore, the spark plasma sintering machine has a feature that the temperature can be rapidly increased and the molding and sintering can be performed in a short time.

The current flowing during heating generates plasma in the gaps between the powder particles, and the plasma activates the powder surface to promote diffusion.

Further, a TiNi alloy sintered body can be obtained by performing spark plasma sintering using a TiNi alloy powder without using a raw powder in order to obtain a high density sintered body. Here, it is conceivable to manufacture a TiNi alloy powder by an atomizing method or the like. However, in the case of the atomizing method, a TiNi alloy must first be manufactured by a melting casting method, and thus there is a problem that it is difficult to control the composition. .

Therefore, in a method of manufacturing a TiNi-based alloy sintered body, after mixing each of Ti powder and Ni powder,
TiN obtained by mechanical alloying from the mixed powder
By using an i-based alloy powder and subjecting the powder to spark plasma sintering, a dense TiNi-based alloy sintered body having a uniform composition can be obtained.

That is, according to the present invention, in a method for producing a TiNi-based alloy sintered body, a TiNi-based alloy is characterized in that after mixing Ti and Ni raw powders, the mixed powder is subjected to spark plasma sintering. A method for manufacturing a sintered body is obtained.

Further, according to the present invention, in a method for producing a TiNi-based alloy sintered body, a powder obtained by mixing raw powders of Ti and Ni and then alloying the mixed powder by a mechanical alloying method. , And a method for producing a TiNi-based alloy sintered body, characterized in that the method comprises the steps of:

[0018]

Embodiments of the present invention will be described below.

First, a first embodiment of the present invention will be described.

In the first embodiment of the present invention, the powder used is a Ti powder (particle diameter 45 μm) produced by an atomizing method and a Ni powder (particle diameter 4 μm) produced by a carbonyl method. 50 of those powders:
50 (at%) ratio (composition range showing shape memory characteristics)
Was mixed in a carbon mold for spark plasma sintering, followed by spark plasma sintering.
The sintering conditions were as follows: heating at a heating rate of 50 ° C./min while compressing at 20 MPa in a vacuum;
For 5 minutes.

As a result, regarding the relative density of the sintered body,
The value was as high as about 95%. From this, it is considered that the sintered body obtained according to the first embodiment of the present invention can be put to practical use.

Next, a second embodiment of the present invention will be described.

In the second embodiment of the present invention, the mechanical alloying method is performed by a rotary ball mill method, the pot is made of SUS304, and the ball (diameter 17 mm) is made of SU.
J-2 was used. The powders used were a Ti powder (particle diameter 45 μm) produced by the atomization method and a Ni powder (particle diameter 4 μm) produced by the carbonyl method. These powders were mixed at a ratio of 50:50 (at%) (composition range showing shape memory characteristics), and were mechanically alloyed for 300 hours at a rotation speed of 100 rpm in an argon gas atmosphere. The weight ratio of the total weight of the mixed powder to the total weight of the balls was 1:50. Since the Ti—Ni alloy powder thus obtained was alloyed in an argon gas atmosphere, the amount of mixed oxygen was small (0.1% or less).
Could be suppressed. This is heat treated (700
When subjected to X-ray diffraction for the sample which had been cooled rapidly by hot water (30 ° C. × 30 minutes), only a TiNi single phase was clearly detected. The obtained alloy powder was filled in a carbon mold for spark plasma sintering, and spark plasma sintering was performed. As the sintering conditions, while compressing at 20 MPa in a vacuum,
The sample was heated at a rate of 50 ° C./min and kept at 1000 ° C. for 5 minutes.

As a result, regarding the relative density of the sintered body,
The value was as high as 98%, and the relative density was further improved as compared with the case of simply mixing the raw material powder of the first embodiment of the present invention. In addition, after the obtained sintered body was further processed and subjected to solution treatment, the actual shape recovery temperature was investigated.
The temperature was about 80 ° C., which was not much different from that obtained by the melt casting method.
From this, it is considered that the sintered body obtained by the present invention can be sufficiently put to practical use.

Next, a third embodiment of the present invention will be described.

In the third embodiment of the present invention, the mechanical alloying method is performed by a rotary ball mill method, the pot is made of SUS304, and the ball (diameter 17 mm) is made of SU.
J-2 was used. The powder used was a Ti powder (45 μm particle size) produced by an atomizing method,
i-X, X = Ni-X alloy powder substituted with at least one metal selected from the group consisting of Cr, Fe, Co, Cu, V, and Mn (the alloy obtained by the melt casting method is roughly pulverized and finely divided). (Ni-X powder having a particle size of 10 μm which was crushed and heat-treated at 300 ° C. in hydrogen). A Ti-Ni-X mixed powder in which the Ti powder and the NiX alloy powder are mixed at a ratio of 50:50 (at%) (composition range showing the shape memory characteristic) (a part of Ni of Ti50Ni50 alloy is replaced with X). 100 rpm in an argon gas atmosphere.
The mechanical alloying method was performed at a rotation speed of 300 hr. Here, the weight ratio of the total weight of the mixed powder to the total weight of the balls was 1:50. The thus obtained Ti-Ni-
The X alloy powder was able to suppress the amount of oxygen mixed in a small amount (0.1% or less) as in Example 2. Further, the obtained alloy powder was filled in a carbon mold for spark plasma sintering, and spark plasma sintering was performed. At this time, the sintering conditions were as follows, while compressing in vacuum at 20 MPa.
The sample was heated at a rate of 50 ° C./min and kept at 1000 ° C. for 5 minutes. Ti obtained from the third embodiment of the present invention
Table 1 shows the relative density of each of the NiX alloy sintered bodies.

[0027]

As shown in Table 1, since the relative density of each of the sintered alloys is as high as 98% or more, even if a part of Ni is replaced by the third element, it can be sufficiently put to practical use. Do you get it.

[0029]

As described above, according to the present invention,
A TiNi-based alloy powder produced by a mechanical alloying method can be put to practical use by producing a sintered body by spark plasma sintering. The TiNi-based alloy has a high relative density and an oxygen content equivalent to that of the melt casting method. An alloy sintered body can be manufactured.

Claims (2)

[Claims] 1. A method for producing a TiNi-based alloy sintered body, comprising mixing raw powders of Ti and Ni and then subjecting the mixed powder to spark plasma sintering. . 2. In a method for producing a TiNi-based alloy sintered body, after mixing raw powders of Ti and Ni, the powder obtained by alloying the mixed powder by a mechanical alloying method is subjected to spark plasma sintering. A method for producing a TiNi-based alloy sintered body, characterized in that: