硝酸塩を焼結助剤としたSi_3N_4及びSi_3N_4/10〜30mass%SiC複合材の常圧焼結とその機械的性質

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Effects of the amount of sintering additives and that of SiC as a second phase on the densification and mechanical properties of Si_3N_4 and Si_3N_4/10-30 mass%SiC composites were examined. Yttrium and aluminum nitrates as sintering additives were added to raw mixtures as methanol solutions. Powder compacts were pressurelessly sintered at 1750℃ for 2h in N_2 atmosphere. The bulk density of the monolithic Si_3N_4 with 4 mass% sintering additives reached 99% T. D. Both of the Si_3N_4/30 mass%SiC with 8 mass% sintering additives and the Si_3N_4/20 mass%SiC with 6 mass% sintering additives were sintered to 94% T. D. Fracture toughness of the dense Si_3N_4/SiC composites decreased compared with that of the monolithic Si_3N_4, due to the inhibitation of β-Si_3N_4 grain growth caused by the addition of SiC. Subsequently, the bending strength of these composites decreased. Furthermore, hardness of these composites increased. On the other hand, in the case of large amount of SiC addition or small amount of sintering additives, composites were not densified sufficiently, and bending strength, fracture toughness and hardness of these composites degraded markedly as compared with these of the monolithic Si_3N_4.
1997-10-01