SiC(w)/Si_3N_4 の強度及び靭性に及ぼすウイスカー表面被覆と配向の効果

概要

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In order to strengthen and toughen Si3N4 ceramics by addition of SiC-whiskers, we tried the control of interfacial properties between whisker and matrix and of orientation of whiskers. For interfacial control, the effects of Al2O3, ZrO2 and carbon coating to the surface of whiskers were studied. The flexural strength and the fracture toughness of Si3N4 composite containing Al2O3-coated whiskers by decomposition of aluminum stearate, were stronger (1107MPa) and larger (10.2MPa·m1/2) than those of the composite with noncoated whiskers. TEM observation revealed that Al2O3-coated whiskers in the composite had smoother surface than non-coated whiskers and that a film-layer was formed at the interface between whisker and matrix. For orientation control, the flexural strength and the creep rupture resistance at 1250°C of Si3N4 composite, reinforced with uni-directionally oriented whiskers by the doctor-blade method, were much stronger (1180MPa) and much larger than those of monolithic Si3N4 ceramics. After creep testing, the new stacking fault and dislocation in the whiskers were observed by TEM. On the basis of these results, the mechanisms of toughening and high-temperature strengthening of SiC(w)/Si3N4 have been discussed.
1991-11-01