Effect of rheological behavior on properties of cast and sintered silicon carbide

This paper describes the rheological behavior of suspensions for two types of SiC powder, termed G-SIC and S-SiC, with different contents of dispersant. In addition, examination of the suspension property and the cast density of the green compacts, together with the mechanical strength of the sintered body, was conducted. Experimental results show that a stable SiC suspension with the lowest viscosity is obtained by controlling the dispersant content at, e.g. similar to 0.1 wt% and similar to 0.25 wt% for 30 vol% of SiC phase for the G-SiC and S-SIC powders, respectively. Cast densities of as high as 68% of theoretical were attainable by using the finer S-SiC powders (having a mean particle size of 0.48 mu m). The suspension with the lowest viscosity associated with the highest cast density cannot be fully considered as a true representation of the final sintered microstructure. Instead, a suspension with appropriate viscosity is needed for optimizing both particle arrangement and packing structure during casting toward a uniformly consolidated compact and sintered structure. The flexural strength of the sintered SIC ceramics is strongly related to the residual pore content, obeying an exponential power law dependence.