JPH0660323B2 - Pressure sintering method for powder material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a method of sintering a powder material, and in particular, a powder metal or a composite powder of the powder metal and a nonmetal such as ceramic is contained in a metal container. Then, the present invention relates to a method of performing canning processing such as pressure compression and extrusion under high temperature and sintering.

<Prior Art> Conventionally, for the purpose of obtaining a homogeneous material without segregation, a fine material having a fine grain size of a structure, or a hard-to-process material having a desired shape, a metal powder material or a non-metal material A canning process is performed in which a composite powder material of (1) and (2) is enclosed in a metal container, which is heated to perform pressure processing or extrusion processing, and after cooling, the container is opened to take out a sintered body inside.

<Problems to be Solved by the Invention> In the conventional canning method described above, the size of the container is hot-compressed, and the powder material inside is also hot-compressed and sintered. In that case, the inner surface of the container is not compressed, and irregularities are likely to occur. The metal forming the container and the internally formed sintered body perform different shrinking actions during cooling after processing due to the difference in Curie point and thermal expansion coefficient. Therefore, especially when processing a brittle material such as a composite material of metal and nonmetal or an intermetallic compound, cracks occur inside the sintered body in the cooling process, starting from the part where the deformation of the container is remarkable. Easy to do. These cracks frequently occur in the corners where the container is irregularly deformed.

This invention, in the above-mentioned canning process,
It is intended to prevent cracks from being generated in the sintered body in the cooling process after the powder material is pressure-sintered in the container.

<Means for Solving the Problems> According to the present invention, a powder material is housed in a metal container, the container is sealed and hot working accompanied by pressurization is performed, and the internal sintered body is used after cooling. In the canning method, when the powder material is stored in the metal container, the plastic graphite sheet is interposed between the inner wall surface of the metal container and the powder material.

As the plastic graphite sheet to be used, for example, "Permuff oil" manufactured by Toyo Tanso Co., Ltd. is suitable, and it is 0.3 to 1 m.
Use one with a thickness of about m. The usage is that all or part of the inner surface of the metal container is attached in advance, especially with emphasis on the corners where cracks frequently occur in the sintered body, or the plastic graphite sheet bag is put in the metal container beforehand. Appropriate method is selected, such as placing or placing a bag of a plastic graphite sheet containing a powder material in a metal container.

As the heating means, an appropriate method such as atmosphere heating, resistance heating, or induction heating can be adopted.However, in order to raise the temperature in a short time, the metal container together with the cold isostatic press is used before the heating. It may be pre-compressed to reduce the porosity of the powder material inside.

In hot pressing for sintering powder material, a metal container is housed in a cylindrical die and pressed by a punch.
In order to reduce irregular deformation of the metal container, the outer diameter of the metal container should be as close as possible to the inner diameter of the die.

<Operation> During compression, the bottom and lid of the container are relatively little deformed, but the peripheral wall of the container, especially the boundary portion between this and the bottom and the lid, is greatly deformed, so that the inner wall surface tends to be uneven. is there. When the powder material comes into direct contact with this inner wall surface and is sintered, the sintered body is formed by digging into these irregularities, so the cooling behavior of the metal container during cooling is different from that of the sintered body. When doing so, a large stress appears in the bite portion, and cracks occur in the sintered body starting from this.

In the present invention, even if unevenness is generated on the inner wall surface of the container during compression, the plastic graphite sheet adapts to this unevenness and is interposed between the plastic graphite sheet and the sintered body. During cooling, the sintered body can perform a contracting operation different from that of the container due to the buffering action and the lubricating action of the plastic graphite sheet, so that stress can be reduced and cracks can be reduced. As a result, even a material such as an intermetallic compound, which has been extremely difficult to process in the related art, can be sintered using powder as a raw material without causing cracks.

<Example> Example 1 An alloy having an atomic% composition of Nd ₂ Fe ₁₄ B was sprayed on a cooling roller to prepare a quenched ribbon having an average thickness of 30μ, which was crushed to have a maximum particle size of 500μ. It was made into a powder having an average particle size of 230μ. This powder did not spontaneously burn in air and was found to have considerable oxidation resistance.

This powder was put into four types of metal containers A and B shown in Table 1,
A plastic graphite sheet having a thickness of 0.4 mm is interposed between C and D and the inner wall surface of the container, and the container is filled as shown in FIG. 1 (a) or FIG. 2 (a). In the case of C, the inside was evacuated by electron beam welding to apply a lid, and in the case of the metal container D, the inside of the vessel was deaerated after applying a lid by argon welding. In the figure, 1 is a container, 2 is its peripheral wall, 3 is its bottom, 4 is a plastic graphite sheet, 5 is raw material powder,
6 is a lid.

The containers A, B, and C in which the powder material is enclosed are housed in a hot press die, and the raw material powder in the container is heated to 700 ° C. by induction heating the die, and the vertical mold 100
It was compressed in the die using a ton compression press.

In the container D in which the powder material was enclosed, the powder material inside was heated to 700 ° C. by induction heating, and loaded in a horizontal 2000 ton hot extruder with the extrusion port closed to be compressed.

After compression, the external dimensions of each container and the dimensions of the sintered body are shown in Table 2. In the figure, 11 is a compressed container, 12 is its peripheral wall, 13 is its bottom, 14 is a plastic graphite sheet, 15 is a sintered body,
16 is the lid of the container.

Comparative Example 1 For comparison, the same powder material as in Example 1 was directly filled in the containers A, B, C and D shown in Table 1 and the result of heating and compression by the same means as in Example 1 was used. It is shown in Table 3.

Example 2 An alloy having an atomic% composition of Nd ₂ Fe ₁₄ B was pulverized by an argon gas atomizing method (average particle size: 150 μ), and this powder was treated in the same manner as in Example 1 with the metal container A shown in Table 1. ,
B, C, and D were filled with a 0.4 mm-thick plastic graphite sheet interposed between the inner wall surface of the container and the container, sealed in exactly the same manner as in Example 1, heated, and compressed. Table 4 shows the dimensions of each part after compression.

Comparative Example 2 For comparison, the same powder material as in Example 2 was directly filled in the containers A, B, C and D shown in Table 1 and the result of heating and compression by the same means as in Example 1 was used. It is shown in Table 5.

Example 3 An alloy having an atomic% composition of Mn-Al is powdered (average particle size 150 μm) by an argon gas atomizing method,
This powder was filled in the same manner as in Example 1 in the metal containers A, B, C and D shown in Table 1 with a 0.4 mm thick plastic graphite sheet interposed between them and the inner wall surface of the container. It was sealed, heated and compressed in exactly the same manner as in Example 1. Table 6 shows the dimensions of each part after compression.

Comparative Example 3 For comparison, the same powder material as in Example 3 was directly filled in the containers A, B, C and D shown in Table 1, and the result of heating and compression by the same means as in Example 1 was measured. It is shown in Table 7.

Comparative Results Table 8 shows the results of examining the presence or absence of cracks by taking out the sintered bodies according to the respective Examples and Comparative Examples described above after cooling.

As described above, even in the case of a material such as an intermetallic compound that easily causes cracks, the powder material could be sintered by the canning process without causing cracks.

<Effects of the Invention> As described above, according to the present invention, it is possible to effectively prevent cracks from being generated in the sintered body when the powder material is sintered by the canning process. Therefore, it is extremely suitable for the sintering process of a composite material of a metal and a nonmetal, or a material such as an intermetallic compound, which easily causes a crack.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a container filled with powder according to an embodiment of the present invention before and after hot pressing, and FIG. 2 is a container having different shapes filled with powder according to an embodiment of the present invention. FIG. 3 is a vertical sectional view before and after hot pressing. 1 and 11 ... Metal container, 4 and 14 ... Plastic graphite sheet, 5 ... Powder material, 15 ... Sintered body.

Claims (1)

[Claims] 1. A powder material is contained in a metal container with a plastic graphite sheet sandwiched between the metal container inner wall surface and the metal container, and the container is sealed to perform hot working accompanied by pressurization. A method for pressure-sintering a powder material characterized.