JPH0566901B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a high-toughness silicon nitride sintered body, particularly for automobile engine parts, wear-resistant parts, cutting tools, etc.
Regarding other industrial parts. Prior Art In order to improve the toughness and strength of silicon nitride sintered bodies, it is considered preferable to grow acicular or columnar particles with a large aspect ratio. In order to obtain such a structure, it is effective to use a Si ₃ N ₄ raw material with a high α rate and to add a specific sintering aid (for example, a rare earth metal oxide such as Y ₂ O ₃ ). It is known that Problems to be Solved by the Invention However, there has been no technical disclosure regarding the structure necessary to most effectively achieve high toughness and strength, such as the size, shape, distribution, amount, etc. of columnar particles. Nakatsuta. Means for Solving the Problems The present inventors focused on the fact that the fracture toughness value and strength of silicon nitride sintered bodies largely depend on the structure of the sintered bodies, and as a result of repeated studies, found that silicon nitride or It was discovered that the distribution state of Sialon particles, especially the size, shape, and amount of particles that grow in a columnar shape, has the most influence, leading to the present invention.In order to achieve high toughness and strength, fine particles and They found that it is most effective to create a structure consisting of grown grains with a high aspect ratio and a grain boundary glass phase. Here, a grown particle with a high aspect ratio is a short diameter of 0.8μ.
m or more and has an aspect ratio of 4 or more, and the amount thereof is preferably 15 to 35% by volume (Vo1) in the sintered body. These grown particles are thought to improve toughness through mechanisms such as crack deflection or particle pull-out, and if the amount is less than 15% by volume, the effect will be small, and if it exceeds 35% by volume, the residual stress in the sintered body will increase. It becomes large and high toughness and strength cannot be obtained. Note that particles with a particle size of less than 0.8 μm or an aspect ratio of less than 4 have a small contribution to improving toughness. Next, the remaining portion preferably consists of fine particles with a short diameter of less than 0.8 μm and a grain boundary phase, and the presence of a considerable amount of coarse particles causes a decrease in strength. The sintered body of the present invention can be obtained by adding and mixing the Si ₃ N ₄ raw material and a sintering aid, shaping the mixture, and then sintering it, or by using the Si raw material as a starting material and adding the sintering aid to it. Other manufacturing methods such as mixing, shaping, heating in a nitrogen-containing atmosphere to nitride, and then sintering can be used; Type of binder,
It is necessary to optimize the amount, sintering conditions, etc. In carrying out the present invention, as a sintering aid
When using substances containing Al such as Al ₂ O ₃ and AlN,
Sialon particles are generated, and the others become nitrogen silicon particles. Example Three types of silicon nitride (Si ₃ N ₄ ) powder shown in Table 1, Y ₂ O ₃ powder (specific surface area 10 m ² /g), and Al ₂ O ₃ powder (10 m ² /g) were mixed at a weight ratio of 90 %Si ₃ N ₄ −5% Y ₂ O ₃ −
After mixing to give 5% Al ₂ O ₃ , they were molded and sintered to create seven types of sintered bodies with different structures. The manufacturing conditions are shown in Table 2. As mechanical properties of these sintered bodies, room temperature strength (JIS R601 three-point bending) and fracture toughness (Chevron notch method) were measured. For microstructural evaluation, mirror-polished samples were observed by SEM, and grain size distribution, aspect ratio, etc. were measured. Table 3 shows the measurement results. In the same table, samples No. 1 to No. 4 show examples of the present invention, and Nos. 5 to 7 show comparative examples. As is clear from these results, high strength and high toughness are achieved in a sintered body in which the ratio of particles with a minor axis of 0.8 μm or more and an aspect ratio of 4 or more is within an appropriate range.

【table】

【table】

[Table] Effects of the Invention As can be seen from Table 3, the sintered body according to the present invention has extremely improved toughness and strength, and can improve the reliability of components, expanding new applications in addition to conventional fields of use. considered to be a thing.

Claims (1)

[Claims] 1 In a sintered body consisting of silicon nitride particles or sialon particles and a grain boundary phase, the silicon nitride particles or sialon particles are formed into columnar shapes or columnar and granular shapes, among which columnar shapes with a short axis of 0.8 μm or more and an aspect ratio of 4 or more are used. Particles account for 15-35% by volume in the sintered body
, and the remainder is composed of columnar particles with a short axis of less than 0.8 μm or an aspect ratio of less than 4 and a grain boundary phase, or the columnar particles, granular particles, and a grain boundary phase. .