GRAIN-BOUNDARY STRUCTURE AND STRENGTH IN HIGH-TEMPERATURE MATERIALS

The fracture strength of high-temperature materials is discussed in connection with grain boundary structure, taking up Mo, Si3N4 and SiC. For molybdenum, in which the fracture strength strongly depends on the grain boundary character, the effects of impurities C, O and N, and TiC addition on the strength of the weakest boundary which may control the fracture strength of polycrystalline material are described. For the non-oxide ceramics, Si3N4 and SiC, the high-temperature strength of sintered materials is described in relation to the grain boundary structure. Further, the effect of covalent bond strength and polarity on the grain boundary structure is discussed referring to the boundary structure observed in SiC and Si bicrystals and AIN-polytype Sialon. © 1990, The Japan Institute of Metals. All rights reserved.