Preparation and properties of reaction bonded silicon carbide (RB-SiC) ceramics with high SiC percentage by two-step sintering using compound carbon sources

A novel processing method to prepare silicon carbide ceramics with a high SiC content by two-step reaction bonding was proposed, using a carbon source composed of fine amorphous carbon black and coarse micro-spherical carbon. The inert carbon particles (coarse micro-spherical carbon) remained present after the process of infiltration of molten silicon and were consumed in the reaction with residual silicon at high temperature. With a soaking time of as short as 5 min at 1550 °C, complete infiltration of Si with reaction to the carbon source could be achieved as the first step, and some coarse carbon may remain present due to incomplete reaction. With the increase in the soaking time and temperature in the second step, the contents of residual carbon and silicon decreased simultaneously through their diffusion-controlled reaction, resulting in an improvement of density and hardness. At 1850 °C, the residual carbon decreased to near zero, accompanied by 6% Si resulting from continuous infiltration of Si during the second-step soaking, and a hardness of 25.3 GPa and a Young's modulus of 443 GPa were achieved. It was clearly demonstrated that the sintering process with the compound carbon source was composed of the fast direct reaction in infiltration, and slow reaction through diffusion, which had the potential to obtain the RB-SiC with a very low content of residual Si.