Fabrication of nanograined silicon carbide by ultrahigh-pressure hot isostatic pressing

Dense nanograined SiC ceramics were obtained by using hot isostatic pressing (HIP). The starting powder was ultrafine beta-SiC powder, which had a mean particle size of 30 nm and contained 3.5 wt % free carbon. SiC powders-both boron-doped and undoped-were densified via HIP under an ultrahigh pressure of 980 MPa at a temperature of 1600 degrees C. Both doped and undoped SiC attained the same density (3.12 g/cm(3)) (relative density of 97.1%). The average grain sizes of boron-doped and undoped SiC were 200 and 30 nm, respectively. The compressive flow stress of undoped SiC was 3 times higher than that of boron-doped SIC at temperatures of 1800 degrees and 1700 degrees C; however, the flow stresses of both materials were almost the same at 1600 degrees C. The HIPed SiC that was doped with boron could be deformed at a stress that was one-third lower than that of hot-pressed boron- and carbon-doped SIC with a grain size of 0.8 mu m.