JPS61159539A - Manufacture of shape memory alloy - Google Patents

Abstract

PURPOSE:To produce the shape memory alloy having a uniform and fine structure without segregation by forming a mixture of >=2 kinds of metal powder into composite powder by a mechanical alloying method and by sintering this composite powder. CONSTITUTION:The mixture of >=2 kinds of metal powder, e.g., a powder mixture of Ti-Ni or Cu-Zn is slightly mixed in an inert gas such as Ar, and is subjected to mechanical alloying in this atmosphere by a mechanical alloying device to form into the composite powder with <=500mu average grain size. This composite powder is then sintered by a hot pressing process or an HIP process to form a sintered body with <=15mu average grain size. By forming this sintered body into prescribed shape, the shape memory alloy excelling in mechanical properties and in fatigue characteristic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing a shape memory alloy having a uniform, fine structure without segregation.

[Technical background of the invention and its problems] Melting methods and powder methods are conventionally known as methods for producing shape memory alloys.

When shape memory alloys manufactured by the melting method are solidified, segregation is likely to occur, with the composition of the first precipitated part and the later solidified part being different, and especially in the case of copper-based alloys, if the crystal grain size is large, There are drawbacks such as deterioration of fatigue properties. Therefore, hot and cold working are necessary to improve the cast structure. However, these alloys have the problem of poor workability.

On the other hand, the commonly used powder method has the disadvantage that the metal powder is treated at a high temperature just below its melting point, so the particle surface is easily oxidized and an oxide film is scattered inside, making it brittle.

In addition, particularly in the case of Ni--Ti alloys, if a simple mixture of Ni and Ti components is sintered, the heat treatment for layering Ni and Ti takes a considerable amount of time, and it is difficult to form a single layer.

[Object of the Invention] The present invention has been made in response to the above-mentioned conventional circumstances, and provides a shape memory alloy that does not cause segregation, has a uniform and fine structure, and has excellent mechanical properties and fatigue properties. The purpose is to provide a manufacturing method for.

[Summary of the invention] That is, the method for producing a shape memory alloy of the present invention involves forming a mixture of two or more metal powders into a composite powder by a mechanical alloying method,
It is characterized in that it is then sintered.

The present invention will be explained in detail below.

A mixture of two or more metal powders refers to each raw material powder with a composition known as a shape memory alloy, such as Ti-
Ni, Qu-Zn, Cu-7n-AI, Pb-Z
Examples include mixed powders such as n-8n. These mixed powders are lightly mixed in an inert gas such as argon gas, and then mechanically alloyed in the same atmosphere using a mechanical alloying device.

The conditions at that time vary depending on the raw material powder used, but it is usually carried out at 50 to 400 rpIX for 0.5 to 24 hours.

The average particle size of the composite powder obtained by this mechanical alloying method is 500 μm.
It is as follows. Among these, 100 μm or less is particularly preferable.

Next, the obtained composite powder is subjected to hot press method or HI
A sintered body that is sintered by the P method and has an average crystal grain size of 15 μm or less, preferably 10 μm or less.

After that, a shape memory alloy can be manufactured by molding it into a predetermined shape. Note that the average crystal grain size of this crystal body is mainly determined by the size of the composite powder used in this previous step.

[Embodiments of the invention] Next, the present invention will be explained by examples.

Example 3 51 parts by weight of Ti powder of 25 mesh and 49 parts by weight of Ni powder of 325 mesh were mixed in an argon atmosphere for 30 minutes using a mixer. Next, the mechanical alloy device was operated at 200 rpm for 5 hours in the same atmosphere. The thus obtained composite powder with an average particle size of 50 μm was vacuum sealed in a mild steel pipe and heated at 900 to 1050°C for 1
The bond and sintered body subjected to HIP for 3 hours at 000 to 2000 atmospheres were taken out.

The physical properties, mechanical properties, and fatigue properties of the obtained Ti-Ni alloy are shown in the table.

In addition, as a comparative example, the results of measuring a cast cut-out material of a Ni-T1 alloy having the same composition as in the example produced by a melting method are also shown in the table.

Note that, as mentioned above, the mechanical properties of the melted material are not sufficient after casting, and the properties are improved through subsequent processing. However, the present invention does not require such processing and can be used immediately with mechanical properties after hot pressing or HIP, and is extremely effective.

[Effect of the Invention J As explained above, according to the method of the present invention, a shape memory alloy with a low degree of segregation and excellent mechanical properties and fatigue properties can be produced.

Claims (4)

[Claims] (1) A method for producing a shape memory alloy, which comprises forming a mixture of two or more metal powders into a composite powder by a mechanical alloying method, and then sintering the mixture. (2) The method for producing a shape memory alloy according to claim 1, wherein the sintering is performed by a hot press method or a HIP method. (3) The method for producing a shape memory alloy according to claim 1, wherein the average grain size of the alloy after sintering is 15 μm or less. (4) The method for producing a shape memory alloy according to claim 1, wherein the composite powder has an average particle size of 500 μm or less.