JPH0556309B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a silicon nitride sintered body, and particularly to a silicon nitride sintered body with improved high-temperature strength. [Prior Art] Silicon nitride sintered bodies have attracted attention as ceramics for automobile engine parts and other high-temperature structures, and are in fact widely used and under development. A typical manufacturing method for silicon nitride sintered bodies is to add appropriate sintering aids such as alumina, yttria, and magnesia to silicon nitride powder, and then process it by pressure molding, injection molding, extrusion molding, casting molding, etc. After being shaped by this method, it is fired to form a sintered body in a non-oxidizing atmosphere, typically a nitrogen atmosphere. The use of sintering aid additives is a factor in strength reduction at high temperatures, and grain boundary phase control of silicon nitride (Si ₃ N ₄ ) crystals has become an issue to ensure use at higher temperatures. There is. Therefore, the present applicant filed Japanese Patent Application No. 61-125906 (Showa
(filed on June 2, 1981) and Japanese Patent Application No. 1982-169 (filed on January 6, 1988, Japanese Patent Application Laid-Open No. 1983-100066), in order to increase the high-temperature strength, a silicon nitride sintered body was proposed. XSiO ₂ N, X ₄ Si ₂ O ₇ N ₂ and X ₁₀ in the grain boundary phase
(SiO ₄ ) ₆ N ₂ [In these formulas, X represents a Group 3A element (including lanthanide series elements) in the long period periodic table. We have proposed a silicon nitride sintered body characterized by precipitating any one or more crystals. This crystal contains Y ₅ N (SiO ₄ ) ₃ , Y ₁₀ N ₂ (SiO ₄ ) ₆ and Y ₂₀ N ₄ where X is yttrium.
(SiO ₄ ) ₁₂ . [Problems to be solved by the invention] In the silicon nitride sintered body proposed by the applicant mentioned above,
The strength at 1000℃ was considerably improved compared to the case where amorphous (glassy) material precipitated at the grain boundaries, but
Although the strength at 1200°C is higher than in the case of amorphous precipitation, it is lower. Therefore, the present invention
An object of the present invention is to provide a silicon nitride sintered body having higher high-temperature strength while suppressing a decrease in strength at 100° C. [Means for Solving the Problems] In order to solve the above problems, the present invention provides a silicon nitride sintered body in which aluminum compound powder and yttrium compound powder are added and sintered to silicon nitride raw material powder. Hexagonal crystals Y ₅ N (SiO ₄ ) ₃ , Y ₁₀ N ₂ (SiO ₄ ) ₆ and Y ₂₀ N ₄ are present at grain boundaries.
(SiO ₄ ) At least one of ₁₂ and YAG
(5Al ₂ O ₃ .3Y ₂ O ₃ ) crystals are precipitated therein. It is preferable that the intensity of the highest intensity diffraction line of the above-mentioned hexagonal crystal and YAG crystal by X-ray diffraction with respect to the highest intensity diffraction line of the β-silicon nitride (Si ₃ N ₄ ) crystal is 0.02 to 0.3, and the intensity ratio is 0.02
If it is smaller, there is no strength improvement effect due to grain boundary crystal phase precipitation, while if the strength ratio is larger than 0.3, a large amount of sintering aid is required in this case, and this large addition reduces the strength at high temperatures. . Typical highest intensity diffraction lines (diffraction peaks) are 211 planes in the above-mentioned Y-N-Si-O hexagonal crystal,
YAG (5Al ₂ O ₃・3Y ₂ O ₃ ) has 420 planes and β-
In Si ₃ N ₄ , the diffraction lines are 101 plane or 210 plane. [Function] Aluminum compounds and yttrium compounds such as alumina (Al ₂ O ₃ ), spinel (MgAl ₂ O ₄ ), and yttrium (Y ₂ O ₃ ), which are sintering aids added to silicon nitride raw material powder, lower the sintering temperature. It becomes a liquid phase at
Then, by cooling slowly (controlled cooling), crystals are precipitated as in the present invention, or amorphous (vitreous) grain boundaries are crystallized by post-firing heat treatment. . Since the Y-N-Si-O based hexagonal crystal and YAG crystal formed by such crystallization form a grain boundary phase, high-temperature strength is improved. [Example] Hereinafter, the present invention will be described in detail by way of embodiment examples with reference to the accompanying drawings. Example 1 Silicon nitride powder (α- _Si3N4 content...95% by volume, average particle size _{... 0.9μm} ) 90wt%, alumina ( _Al2O3 ) powder 5wt%, and ittria ( _{Y2O3 )}
A powder mixture having a powder composition of 5 wt % was mixed with a thermoplastic resin, and the kneaded mixture was injection molded into a rod-shaped body of 5 x 5 x 50 mm. Degrease (remove resin) before sintering,
Si ₃ N ₄ sintered body samples 1 to 5 were obtained by sintering under the sintering conditions shown in Table 1. These sintered bodies were ground to a size of 3×4×40 mm, and in particular, samples 2, 4, and 5 were subjected to post-heat treatment under the heat treatment conditions shown in Table 1. Note that the post-heat treatment is performed to change the grain boundary phase of the silicon nitride sintered body from an amorphous (glassy) phase to a crystalline phase. The surface of the obtained sample was subjected to X-ray diffraction to identify the crystal phase, and the results are shown in Table 2.

【table】

〔Effect of the invention〕

According to the present invention, in the silicon nitride sintered body, β
-By precipitating Y _- N- _Si - _O hexagonal crystals such as _Y20N4 ( _SiO4 ) ₁₂ and YAG crystals at the grain boundaries of Si3N4 grains, the high temperature of the sintered body can be reduced. Strength (1000
℃ or higher).

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between test temperature and four-point bending strength of a silicon nitride sintered body, and FIG. 2 is a graph of an X-ray diffraction pattern of a silicon nitride sintered body according to the present invention. , FIG. 3A is a diagram showing the relationship between the X-ray diffraction intensity and four-point bending strength of Y ₂₀ N ₄ Si ₁₂ O ₄₈ at 1000°C, and FIG.
FIG. 4A is a diagram showing the relationship between the X _- ray diffraction intensity and the _{four - point} bending strength of YAG at 1200°C. FIG. 4B is a diagram showing 1200℃
FIG. 3 is a diagram showing the relationship between the X-ray diffraction intensity and the four-point bending strength of YAG.

Claims (1)

[Claims] 1. In a silicon nitride sintered body obtained by adding and sintering aluminum compound powder and yttrium compound powder to silicon nitride raw material powder, hexagonal crystals Y ₅ N (SiO ₄ ) ₃ are present at the sintered body grain boundaries. , Y ₁₀ N ₂ (SiO ₄ ) ₆ and
Y ₂₀ N ₄ (SiO ₄ ) At least one of ₁₂ and YAG
(5Al ₂ O ₃・3Y ₂ O ₃ ) crystal is precipitated. 2. A patent claim characterized in that the intensity of the highest intensity diffraction line of the hexagonal crystal and YAG crystal in X-ray diffraction with respect to the highest intensity diffraction line of the β-silicon nitride (Si ₃ N ₄ ) crystal is 0.02 to 0.3. The silicon nitride sintered body according to item 1.