Effect of carbon fiber volume fraction on 6H to 4H-SiC polytype transformation

In this study, polycrystalline -SiC composed of 55.7wt.% 6H-SiC, 35.1wt.% 4H-SiC with different volume fractions of carbon fibers (0-5-10-15-20%) was successfully sintered by spark plasma sintering technique at 2000 degrees C and 35MPa of applied pressure. The micrographs obtained from scanning electron microscopy revealed that the sintered samples were composed of equiaxed SiC grains. Results indicated that the presence of carbon fibers retarded the SiC densification process, decreased their relative densities and increased their porosity. Additionally, according to quantitative phase analysis by the Rietveld method during the sintering step, it was found that the 6H to 4H transformation has taken place. Increasing the carbon fibers content accelerated this trend as the sample containing 20vol.% carbon fiber was consisted of 85.5wt.% 4H-SiC.