High-temperature ablation of hot-pressed HfC-SiC ceramics

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 & DEG;C for 1 h at 50 MPa and displayed a fine microstructure with an average grain size of & SIM;5 & mu;m and a Vickers hardness of 22.9 & PLUSMN; .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 & mu;m/s.