Process-tolerant pressureless-sintered silicon carbide ceramics with alumina-yttria-calcia-strontia

Abstract

Process-tolerant SiC ceramics were prepared by pressureless sintering at 1850–1950°C for 2h in an argon atmosphere with a new quaternary additive (Al2O3-Y2O3-CaO-SrO). The SiC ceramics can be sintered to a>94% theoretical density at 1800–1950°C by pressureless sintering. Toughened microstructures consisting of relatively large platelet grains and small equiaxed grains were obtained when SiC ceramics were sintered at 1850–1950°C. The presently fabricated SiC ceramics showed little variability of the microstructure and mechanical properties with sintering within the temperature range of 1850–1950°C, demonstrating process-tolerant behavior. The thermal conductivity of the SiC ceramics increased with increasing sintering temperature from 1800°C to 1900°C due to decreases of the lattice oxygen content of the SiC grains and residual porosity. The flexural strength, fracture toughness, and thermal conductivity of the SiC ceramics sintered at 1850–1950°C were in the ranges of 444–457MPa, 4.9–5.0MPam1/2, and 76–82Wm−1K−1, respectively.