Effect of sintering techniques on the microstructure of liquid-phase-sintered SiC ceramics

Phase composition and microstructures of SiC ceramics with Al2O3 and Er2O3 as sintering additives were compared, which were prepared by pressureless liquid-phase sintering (PLPS), hot pressing sintering (HPS), and spark plasma sintering (SPS), respectively. Despite the different sintering temperatures and pressures, all samples were almost fully densified and exhibited fine-grained microstructure. Only SiC crystallized phase was detected in the SPS SiC because of the low sintering temperature and high cooling rate, while the ErAlO3 phase accompanied with a designed Er3Al5O12 phase was detected in the HPS SiC because of the absence of powder bed, which led to partial volatilization of Al2O3 powder at a higher sintering temperature. No obvious orientational growth of SiC grains was observed in all these ceramics, except a few 4H SiC grains along <1 0 0> axis in the SPS SiC. In addition, SiC–SiC grain boundary films differed from each other in these SiC ceramics.