High‐temperature ablation of hot‐pressed HfC–SiC ceramics

Abstract Effective thermal insulation materials rely on the fabrication of dense, ultra‐high‐temperature ceramics that can withstand harsh environments. Hafnium carbide‐based ceramics are one of the leading materials that have the potential to perform relatively well in high‐temperature oxidizing environments under mechanical loading due to their thermal and mechanical stability. In this study, we explore the effects of processing conditions to create dense, ablation‐resistant HfC–SiC composites with a fixed composition of HfC–20 wt.% SiC using a hot‐pressing method. Sintering pressure, temperature, and time were varied and the material's relative density, phase composition, morphology, microstructure, and hardness were investigated. Composite ceramics with 99% relative density relative to a theoretical value were created by hot pressing at 2100°C for 1 h at 50 MPa and displayed a fine microstructure with an average grain size of ∼5 µm and a Vickers hardness of 22.9 ± .8 GPa. The mass loss was determined using an oxyacetylene torch with cross‐section investigations of oxide surface formations and subsurface microstructural changes. These HfC–SiC samples developed a 410 nm hafnium oxide layer on the surface upon torch exposure and had an average calculated recession rate of .028 µm/s.