JPS63203733A - Manufacture of shape memory alloy - Google Patents

Abstract

PURPOSE:To manufacture a sintered compact of Ti-Ni shape memory alloy minimal in O2 content, by filling a mixture of powdered TiH2 and Ni into a cylindrical body made of specific metal, by sucking H2 generated by the decomposition of TiH2 from one end of the cylindrical body while applying heating, and by reducing NiO, etc., in Ni by H2. CONSTITUTION:The cylindrical body 1 made of one kind among the metals such as Fe, Ni, Cu, etc., or alloys thereof is filled with the powder mixture A of TiH2 and carbonyl Ni powders of <=100 mesh, which is put into a heating furnace and heated up to 800-1,200 deg.C while sucking and evacuating the atmosphere in the cylindrical body 1 by means of an exhaust pump 3 through a pipe 2 attached to one end of the metallic cylindrical body 1. NiO in Ni is reduced by H2 gas generated by the decomposition of TiH2, O2 contained in Ni is removed, and respective powders of Ti and Ni are sintered. When the generation of H2 gas is finished, the metallic cylindrical body 1 is hermetically sealed and then extruded or forged into the required shape, and successively, the metallic cylindrical body 1 is removed by means of grinding, etc. In this way, the Ti-Ni shape memory alloy of <=0.15% O2 content and >=95% true density ratio can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The present invention relates to a method for producing a high-density Tb N= rhombic shape memory alloy having high plastic workability and excellent shape memory effect.

<Conventional technologies and their problems> Conventionally, methods for producing shape memory alloys include melting and casting methods such as (1) high-frequency vacuum induction melting, (2) arc melting, and (3) electron beam melting. A powder metallurgy method is known in which powder and powder are mixed and sintered.

However, the conventional shape memory alloy manufacturing method described above has the following problems.

That is, since the high frequency vacuum induction melting method (1) uses a graphite crucible, a reaction occurs between the molten metal and the crucible, and carbon enters the molten metal. This carbon precipitates as ThC and acts as a cause of fatigue failure, leading to a reduction in fatigue life. (In the arc melting method described in 2, an ingot with a uniform composition is
hard. (3) Electron beam melting method is expensive;
It is also difficult to handle. Ingots obtained by these melting methods undergo large work hardening during processing, have poor plastic workability, and require many steps to form into a product.

On the other hand, the powder metallurgy method has easier composition control than the melt casting method and can obtain alloys with a uniform composition, but because the oxygen concentration in the raw material fine powder is high, the oxygen concentration of the sintered body is lower than that of the melt casting method. This has the disadvantage that the plastic workability is even worse as it is higher than that of the steel.

Means for Solving the Problems> The present inventors have studied to solve the above-mentioned problems of the conventional methods for manufacturing shape memory alloys, and as a result they have arrived at the present invention.

That is, in the present invention, a mixed powder containing TbH2 powder and Chen powder as main raw materials is filled into a metal cylinder whose one end is sealed, and then the metal cylinder is heated for 8 hours while being sucked from the other end by an exhaust pump or the like.
After heating to a temperature of 00 to 1,200°C and completing the generation of hydrogen gas, the cylinder is sealed, and then the heated sealed metal cylinder is extruded or subjected to II processing, and the metal cylinder is removed to reduce the amount of oxygen to 0. The present invention provides a method for obtaining a shape memory alloy based on TL-1' having a true density ratio of 15% or less and a true density ratio of 95% or more.

Function> As described above, in the method of the present invention, a mixed powder containing TL He powder with a low oxygen content and Ni powder as main raw materials is used, and this is filled into a metal cylinder with one end sealed. However, in this case, the mixed powder may be molded in advance by pressing, CIP, etc., or it may be filled as a powder.

Carbonyl Ni powder, reduced Ni powder, etc. are used as the powder, but it is not necessary to particularly refine the raw material powders such as Tb He powder and Ni powder. Therefore, oxidation contamination of the raw material powder during mixing can be avoided, and the oxygen concentration in the sintered body will not be increased more than necessary.

Next, the money used in this invention! The cylindrical body is preferably made of a material that is highly workable, and its shape may be cylindrical or rectangular. Further, in order to remove the metal cylinder after extrusion or forging, there are a method of mechanically removing it by polishing or the like, and a method of chemically removing it with a corrosive liquid such as acid. Considering the above points comprehensively, the material for such a metal cylinder should be at least one of iron, nickel, copper, etc.
Preference is given to metals consisting of seeds or alloys based on one of these metals.

When a mixed powder of LH2 powder and Chen powder is filled in a metal cylinder and heated, it reaches a temperature of about 600°C or more at 21ir! 1 to “f H
e The powder decomposes and generates hydrogen gas. When this is heated to a temperature of 800 to 1200° C. while being sucked by an exhaust pump, the generated hydrogen gas reduces the cationic oxides contained in the powder and removes the oxygen contained therein. When the generation of hydrogen gas is completed, the mixed powder is sintered and the amount of oxygen contained in this sintered body is ideally only the amount of oxygen originally contained in the n H2 powder.

Here, the heating temperature was set at 800 to 1200°C.
At temperatures below 0°C, it takes a long time to decompose 'l lb, causing the problem of longer heating times, and at temperatures above 1200°C, grain growth in the sintered body increases and the crystal grain size increases, resulting in poor workability. This is because the raw material powder may be dissolved, or the raw material powder may be dissolved in some cases. After this metal cylinder is sealed, the uNi alloy inside can be made to have a true density ratio of 95% or more by processing it by extrusion or forging.

After that, this metal cylinder is removed by polishing, pickling, etc. Due to its low oxygen content, it has excellent plastic workability and fatigue properties, and because it has a uniform composition, it has an excellent shape memory effect. Therefore, it is possible to produce a shape memory alloy based on T'b ft-.

<Example> Hereinafter, this invention will be explained in detail with reference to Examples.

LH2 powder of 100 mesh or less (oxygen amount 2100 pl
)TI>45.8% by weight and carbonyl group powder oxygen content 1soppn) 54.2% by weight were mixed in an attritor and sieved to 100 mesh or less.

After CIP-processing and molding this raw material powder at 3 t/d in advance, this molded mixed powder A was molded into a mold with an outer diameter of 70 a x an inner diameter of 5
The mixture was filled into a continuous metal cylinder 1 measuring 0M×200U in length, and inserted into a heating furnace while being pulled by an exhaust pump 3 through a pipe 2 attached to the tip of the metal cylinder 1, and heated to 1000°C. After about 2 hours of heating after insertion, no hydrogen generation was observed, so the base of pipe 2 was tightly sealed, the pipe was removed, and in that state extrusion processing was performed to a diameter of 18 mm. Thereafter, the outer periphery of the Ni gold metal cylinder was removed by grinding to obtain a ThNi gold alloy.

The oxygen content of this alloy was 11010 pp, and the density was 98.2% of the true density ratio.

For comparison, π powder of the same particle size (oxygen 12,700 ppm
) 44.8% by weight and carbonyl Nπ powder (oxygen content 150%
0ppIl) 55.2% by weight was mixed at 7t/
Cold pressing was carried out in aj. The obtained compact was 100
Vacuum sintering was performed at 0°C for 5 hours. The Ichi-chen alloy obtained after sintering had an oxygen content of 2030 pl) 1 m, and a density of only 87.8% of the true density ratio. Also, these IL
When the -a alloy was subjected to cold wire drawing, the material obtained by this invention could be plastically worked with a total working rate of 93% or more, but in the case of the comparative material, the total working rate was only 75%. There wasn't.

<Effects of the Invention> As explained above, according to this invention, Th H2 and N
By using a mixed raw material powder of Moreover, a dense alloy can be provided by subsequent extrusion or forging after heating.

[Brief explanation of the drawing]

The drawing is a schematic view showing the gold 1t5 body used in the manufacturing method of the present invention and the operation with the cylinder.

Claims (2)

[Claims] (1) After filling a mixed powder containing TiH_2 powder and Ni powder as main raw materials into a metal cylinder with one end sealed, the metal cylinder is heated to 800~1
T characterized by heating to a temperature of 200°C and sealing after completion of generation of hydrogen gas, then extruding or forging the heated sealed metal cylinder, and then removing the metal cylinder.
A method for producing an i-Ni shape memory alloy. (2) The obtained Ti-Ni sintered alloy has an oxygen content of 0.15
% or less, and the true density ratio is 95% or more.