Microstructure of spark plasma sintered silicon carbide with Al-B-C

Abstract

Densification of SiC powder with total amounts of 2, 4, 8 wt% Al-B-C additive was carried out by spark plasma sintering (SPS). The unique features of the process are the possibilities of a very fast heating rate and a short soaking time to obtain fully-dense materials. The heating rate and applied pressure were kept at 100 K . minute(-1) and 40 MPa, while the sintering temperature and soaking time varied from 1,700-1,800 degrees C for 10-40 minutes, respectively. The SPS-sintered SiC at 1,800 degrees C with different amounts of Al-B-C reached near-theoretical density. The sintered SiC ceramics were predominantly composed of 6H polytype with 15R and 4H polytype as minor phases. The microstructure of SiC sintered up to 1,750 degrees C consisted of equiaxed grains. In contrast, the growth of large elongated SiC grains in small matrix grains was shown in sintered bodies at 1800 degrees C, and a plate-like grains interlocking microstructure had been developed by increasing the soaking time at 1800 degrees C. The grain growth rate decreases with increasing amounts of Al-B-C in SiC, however, the volume fraction and the aspect ratio of large elongated SiC grains in the sintered bodies increased.