常圧焼結炭化けい素の曲げ強度と破壊靭性に及ぼすビッカース圧入荷重と微視組織の影響
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Vickers hardness, four-point bending tests and fracture toughness evaluation by means of two kinds of indentation methods (ISB and IF methods) were conducted on normal-sintered silicon carbide (SiC). To investigate the microstructure on the hardness, H<SUB>V</SUB>, the bending strength, σ<SUB>f</SUB>, and the fracture toughness, K<SUB>I</SUB>C, three kinds of SiC materials (materials A, B and C) with different sintering temperatures were prepared. Material A, of lowest sintering temperature, had the smallest grain, lower density and higher porosity. On the other hand, material C, of highest sintering temperature, had abnormal grown grains, higher density and a lower porosity which were equal to material B. The H<SUB>V</SUB> decreased with increasing indentation load, P, for all three materials. The indentation shapes were comparatively clear, and on the fracture surface of materials A and B, four cracks initiated from the four vertices of the indentation as clear radial and median cracks. For material C, a part of the surface peeled off due to the effect of lateral cracks on the surface layer, and the fracture surface was not flat. The σ<SUB>f</SUB> decreased with increasing P for all three materials. The σ<SUB>f</SUB> of material C was smaller than those of the other materials for the smooth specimens, and the variation of the σ<SUB>f</SUB> of material C was larger than the other materials for the smooth and precracked specimens in all cases. The K<SUB>I</SUB>C determined by the ISB method was smaller than that by the IF method in the same P condition, and the K<SUB>I</SUB>C by the IF method decreased with increasing P and was saturated in the range of P ≥ 10 N.
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