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

Process-tolerant SiC ceramics were prepared by pressureless sintering at 1850-1950 degrees C for 2 h 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 degrees 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 degrees C. The presently fabricated SiC ceramics showed little variability of the microstructure and mechanical properties with sintering within the temperature range of 1850-1950 degrees C, demonstrating process-tolerant behavior. The thermal conductivity of the SiC ceramics increased with increasing sintering temperature from 1800 degrees C to 1900 degrees 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 degrees C were in the ranges of 444-457 MPa, 4.9-5.0 MPa m(1/2), and 76-82 Wm(-1) K-1 respectively.