ABSTRACT HfC–SiC is one of the leading thermal insulation ceramics that has the potential to perform well under high thermomechanical loads. In this study, we explore the use of pressureless sintering to produce this material at relatively low temperatures (2100°C) and focus on understanding the effect of adding WC, in the 0 to 20 wt.% range, on its ablation resistance. The sintered samples were evaluated for their relative density, phase composition, morphology, microstructure, Vickers hardness, and bending strength. The relative density and the Vickers hardness increased from 89% to 97% and from 13.0 to 18.4 GPa, respectively, when the WC content increased from 0 to 20 wt.%. A relatively high value of 480 MPa for the bending strength was measured for the sample with 10 wt.% WC, which was attributed to the more refined microstructure. Oxyacetylene torch testing in tandem with cross‐section micrographs and elemental composition mapping revealed that the addition of WC increased protection in an ablative environment. The observed enhanced oxidation protective ability of these UHTCs is linked to the retention of Si during the ablation process to form an amorphous Hf–Si–W–O overlayer. The retention of Si ensures that a glassy and viscous silicate phase is formed on the surface of the sample. This protective oxide phase restricts volatile oxide phase formation and thus reduces surface porosity and oxygen diffusion. In addition, the viscous tungsten‐silicate phase provides self‐healing of surface defects and improves bending strength.
Doolittle et al. (Tue,) studied this question.