SiCウィスカー/Si3N4複合セラミックスの機械的性質に及ぼす焼結助剤量とウィウカー量の影響

概要

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The effects of contents of Y2O3 sintering aid (4-14 mol%) and SiC whisker (SiC(w): as-received one (5-30 vol%) and sieved one (20 vol% only)) on the transverse-rupture strength and fracture toughness of SiC(w)/Si3N4-Y2O3-6 mol%Al2O3 composite ceramics were investigated, paying attention to the changes in the grain boundary phase, the size of acicular Si3N4 grains and the fracture source. Results obtained were as follows: (1)Both the strength and toughness of the composites with 20 vol% as-received-and sieved-SiC(w) became a maximum at 8 mol%Y2O3, in the same way as the monolith. This was con-sidered mainly due to the largest acicular Si3N4 grain size and partly to the appearance of grain boundary phase of 5Y2O3⋅Si3N4⋅Al2O3 at such a Y2O3 content. (2)With increasing SiC(w) content, the strength decreased in spite of the increase in the toughness, which was attributed to the increase in the size of microstructural defects as a fracture source. (3)In spite of higher strength level of the specimens than those in the other reports, the fracture sources were large Si3N4 aggregate of 10-50 pm in the monolith, SiC(w) aggregate of 60-190 μm in the composite with as-received SiC(w) and SiC(w) aggregate of 18-80 μm in the composite with sieved SiC(w).
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