Effects of Starting Materials on Preparation and Properties of Pure SiC Ceramics via the HTPVT Method

The method of high temperature physical vapor transport (HTPVT) is an available approach to prepare silicon carbide (SiC) ceramics with high density and high purity. In the present work, α-SiC (6H-SiC) and β-SiC (3C-SiC) powders were used as starting materials respectively to fabricate SiC ceramics with HTPVT process, and the effects of starting materials on nucleation, density, microstructure and mechanical properties of SiC ceramics were investigated. It showed that at high temperature, the decomposition rate of β-SiC was higher than that of α-SiC, and at the initial nucleation stage, the average grain size of SiC crystal obtained with β-SiC starting materials was smaller than that with α-SiC starting materials, because higher vapour pressure of gas phase which decomposed by β-SiC starting materials facilitated nucleation and growth of SiC grains. Density of the resulted SiC ceramics using α-SiC and β-SiC as starting materials was 3.16 g·cm-3 and 3.17 g·cm-3, indicating close values, while, using β-SiC as the starting materials, the grain size was smaller, consequently, the flexure strength was higher. Increasing growth temperature from 2200°C to 2300°C, the densities and the flexure strength of the SiC ceramics using either α-SiC or β-SiC were decreased.