JPH01316401A - Pressurized sintering method for powder material - Google Patents

Abstract

PURPOSE:To prevent the generation of cracks in sintered parts during the cooling process thereof by interposing a plastic graphite sheet between the inside wall of a metallic container and raw material powder at the tie of putting the powder raw materials prepd. by mixing powders of various kinds of metals and alloys or further powders of ceramics into the metallic container and subjecting the materials to pressurized sintering at a high temp. CONSTITUTION:The powders 5 of various kinds of the metals or alloys or the composite powder 5 prepd. by mixing the nonmetallic powders of the various ceramics, etc., further with the powders of said metals and alloys are packed into the container 1 made from a carbon steel, stainless steel, etc. The plastic graphite sheet 4 having, for example, 0.3-1mm thickness is interposed between the inside wall of the container 1 and the raw material powders. A cap 6 consisting of the same material as the material of the container 1 is welded to the container and the container is put into a die and is subjected to pressurizing and sintering to a prescribed shape at and under a high temp. and high pressure; thereafter, the container is cooled and the molding is taken out of the container. The generation of the cracks in the sintered body is obviated even if the container 11 and the sintered body 15 are cooled at different shrinkage rates by the buffer effect and lubricating effect of the graphite sheet 14.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for sintering powder materials, and in particular, a method for sintering powder materials, in particular, a method for storing powder metal or a composite powder of the same and a non-metal such as ceramic in a metal container. The present invention relates to a method of performing canning processing such as pressure compression or extrusion at a high temperature and sintering.

<Conventional technology> Conventionally, in order to obtain homogeneous materials without segregation, dense materials with fine grain sizes, and difficult-to-process materials with desired shapes, metal powder materials or combinations of these with non-metals have been used. A canning process is performed in which a composite powder material with a sintered body is sealed in a metal container, heated and pressurized or extruded, and after cooling, the container is opened and the sintered body inside is taken out.

<Problems to be Solved by the Invention> In the conventional canning method described above, the dimensions of the container are hot-pressed, and the powder material inside is also hot-pressed and sintered accordingly. In that case, the inner surface of the container remains flat and is not compressed, which tends to cause irregular irregularities. The metal forming the container and the sintered body made inside contract differently when cooled after processing due to differences in their Curie points and coefficients of thermal expansion. When processing brittle materials such as composite materials and intermetallic compounds, cracks tend to occur inside the sintered body during the cooling process, starting from areas where the container is significantly deformed. It often occurs in corner areas where irregular deformation is common.

In the above-mentioned canning process, this invention provides
This is intended to prevent cracks from forming in the sintered body during the cooling process after the powder material is sintered under pressure in a container.

Means for Solving the Problems> This invention stores a powder material in a metal container, seals the container, performs hot working accompanied by pressure, and uses the sintered body inside after cooling. In the canning processing method, when a powder material is housed in a metal container, a 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, "Permafoil" manufactured by Toyo Tanso Co., Ltd. is suitable, and the
Use one with a thickness of about 1cm.

To use it, paste it in advance on all or part of the inner surface of the metal container, focusing on the corners where cracks occur frequently in the sintered compact, or place the bag of plastic graphite sheet inside the metal container in advance. Choose an appropriate method, such as placing the powder material in a plastic graphite sheet bag containing the powder material in a metal container.

In addition, as a means of heating, an appropriate method such as atmospheric heating, resistance heating, induction heating, etc. can be adopted, but in order to raise the temperature within a short time, the metal container must be heated using cold isostatic press, etc. prior to heating. may be pre-compacted to reduce the porosity of the internal powder material.

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

<Function> During compression, the bottom and lid of the container are relatively less deformed, but the peripheral wall of the container, especially the boundary between this and the bottom and lid, is significantly deformed, which tends to cause unevenness on the inner wall surface. It is. When sintering is performed by directly contacting the powder material with this inner wall surface, the sintered body is formed by digging into these irregularities, so the metal container exhibits a shrinkage behavior different from that of the sintered body when cooled. When this occurs, a large stress appears at the biting part, and this causes cracks to occur in the sintered body.

In this invention, even if the inner wall surface of the container is uneven during compression, the plastic graphite sheet is interposed between the sintered body and the plastic graphite sheet to adapt to the unevenness. During cooling, the buffering and lubricating effects of the plastic graphite sheet allow the sintered body to contract in a manner different from that of the container, thereby reducing stress and reducing the occurrence of cracks. As a result, even materials such as intermetallic compounds, which were conventionally extremely difficult to process, can be sintered from powder without causing cracks.

<Example> Example 1 An alloy having an atomic % composition of Nd2Fe+J was thermally sprayed onto a cooling roller to form a quenched ribbon with an average thickness of 30μ, and this was crushed to obtain a maximum particle size of 500p and an average particle size of 23p.
It was made into a powder of 0 liters. This powder did not spontaneously combust in air and was found to have considerable oxidation resistance.

This powder was poured into four types of metal containers A, B, and C shown in Table 1.
, D, a plastic graphite sheet with a thickness of 0.4 cm is interposed between it and the inner wall surface of the container as shown in FIG. 1(a) or FIG. 2(a).
In the case of metal containers A, B, and C, the inside is evacuated by electron beam welding and a lid is applied, and in the case of a metal container, after the lid is applied by argon welding, the inside of the container is evacuated. I felt it. In Figure 1, l is a container, 2 is its peripheral wall, 3 is its bottom, 4 is a plastic graphite sheet, 5 is a raw material powder, and 6 is a lid.

Table 1 (Container specifications) Containers A, B, and C filled with powder materials are placed in a hot press die, and the raw material powder in the containers is heated to 700°C by induction heating the die. The mixture was heated and compressed in the die using a vertical 100 ton compression press.

The container containing the powder material is heated to 700°C by induction heating, and the container is a horizontal type 20 with the extrusion port closed.
00 )-n hot extruder and compressed.

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

Table 2 (Example 1) Comparative Example 1 For comparison, the same powder material as in Example 1 was directly filled into containers A, B, C, and D shown in Table 1, and the same powder materials as in Example 1 were filled. The results of heating and compression are shown in Table 3.

Table 3 (Comparative Example 1) Example 2 An alloy having an atomic percent composition of Nd2Fe14B was powdered by an argon gas atomization method (average particle size 150μ)
Similarly to Example 1, this powder was placed in metal containers A, B, C, and D shown in Table 1, with a thickness of 0.0 mm between the inner wall surface of the container and the metal containers A, B, C, and D shown in Table 1.
It was filled with a 4 mm plastic graphite sheet interposed therebetween, sealed, heated, and compressed in exactly the same manner as in Example 1. Table 4 (Example 2) Comparative Example 2 For comparison, the same powder material as in Example 2 was placed directly into containers A, B, C, and D shown in Table 1. Table 5 shows the results of filling and heating and compressing in the same manner as in Example 1.

Table 5 (Comparative Example 2) Example 3 An alloy nominally having an atomic % composition of Mn-An was powdered by an argon gas atomization method (average particle size 150
p) Lz, this powder was placed in the metal containers A, B, C, and D shown in Table 1 in the same manner as in Example 1, with a plastic graphite sheet having a thickness of 0.41 cm interposed between the inner wall surface of the container. Let it fill and fill it.
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.

Table 6 (Example 3) Comparative Example 3 For comparison, the same powder materials as in Example 3 were directly filled into containers A, B, C and D shown in Table 1, and the same powder materials as in Example 1 were filled. Table 7 shows the results of heating and compression.

Table 7 (Comparative Example 3) Comparison Results The sintered bodies according to each Example and each Comparative Example were taken out from the container after cooling and inspected for the presence of cracks.
(Comparison results) 0... No cracks in the sintered body △... Traces of cracks in the sintered body ×...
Cracks in the sintered body As described above, even in the case of materials that tend to generate racks, such as intermetallic compounds, the powder material could be sintered by canning processing without generating cracks.

<Effects of the Invention> As described above, according to the present invention, it is possible to effectively prevent cracks from occurring in a sintered body when sintering a powder material by canning processing. Therefore, it is particularly suitable for sintering materials that are prone to cracking, such as metal-nonmetal composite materials and intermetallic compounds.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a container filled with powder in an embodiment of the present invention before and after hot pressing, and FIG. 2 is a container of a different shape filled with powder in an embodiment of the present invention. FIG. 3 is a vertical cross-sectional view of before and after hot pressing. 1 and 11...Metal container, 4 and 14...Plastic graphite sheet, 5...Powder material, 15...Sintered body. Patent applicant: Sanyo Special Steel Co., Ltd. Agent: Satoshi Shimizu and 2 others

Claims (1)

[Claims] (1) A powder material is stored in a metal container with a plastic graphite sheet sandwiched between it and the inner wall surface of the metal container, and the container is sealed to perform hot working accompanied by pressurization. Pressure sintering method for powder materials.