Microstructure and mechanical properties of self-reinforced alpha-silicon carbide

Fine (0.46 mu m) alpha-SiC powders with or without large (21 mu m) alpha-SiC particles (seeds) added were pressureless-sintered at 1900 degrees C for 1, 4, and 8 h with addition of yttrium aluminum garnet (YAG). The introduction of larger seeds into fine alpha-SiC accelerated the grain growth of some alpha-SiC grains and resulted in self-reinforced microstructure consisted of large elongated grains and small equiaxed grains. In contrast, the material without seeds had a relatively equiaxed grain structure. Development of self-reinforced microstructure results in significant improvements in toughness. However, the improved toughness is offset by a significant reduction in strength. The fracture toughness of the 8-h sintered materials without or with seeds was 4.6 and 6.2 MPa m(1/2), respectively. (C) 1998 Elsevier Science Limited and Techna S.r.l.