PRESINTERING HEAT-TREATMENT, DENSIFICATION, AND MECHANICAL-PROPERTIES OF SILICON-CARBIDE

Silicon carbides were subjected to extended heat treatments at 1400-degrees or 1600-degrees-C prior to a 1-h isochronal sintering at 2000-degrees-C in argon, and the resulting microstructures, final densities, and room-temperature four-point bend strengths were compared to those of samples prepared without the pretreatments. The samples heat-treated at 1600-degrees-C exhibited higher relative densities and flexure strengths. Microstructural observation revealed that the heat treatment at 1600-degrees-C modified the initial powder compact microstructure, decreasing the development of large. dense domains in the early and intermediate sintering stages. This evolution was considered to promote a more uniform subsequent densification. The final size and distribution of the grains as well as of the pores were found to be affected favorablv by the pretreatment.