Journal of the Ceramic Society of Japan
Online ISSN : 1882-1022
Print ISSN : 0914-5400
Effects of Nitrate Sintering Additives on Pressureless Sintering of Monolithic Si3N4 and Si3N4/10-30mass% SiC Composites and Their Mechanical Properties
Jae-Yuk KIMTakayoshi ISEKIToyohiko YANO
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1997 Volume 105 Issue 1226 Pages 837-841

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Abstract

Effects of the amount of sintering additives and that of SiC as a second phase on the densification and mechanical properties of Si3N4 and Si3N4/10-30mass% 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°C for 2h in N2 atmosphere. The bulk density of the monolithic Si3N4 with 4mass% sintering additives reached 99% T. D. Both of the Si3N4/30mass% SiC with 8mass% sintering additives and the Si3N4/20mass% SiC with 6mass% sintering additives were sintered to 94% T. D. Fracture toughness of the dense Si3N4/SiC composites decreased compared with that of the monolithic Si3N4, due to the inhibitation of β-Si3N4 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 Si3N4.

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