Qualitative analysis of hafnium diboride based ultra high temperature ceramics under oxyacetylene torch testing at temperatures above 2100 °C

Oxidation tests were carried out on HfB2–SiC, HfB2–HfC, HfB2–WC–SiC, and HfB2–WSi2 ceramics using an oxyacetylene torch. The samples were oxidized between 2100 and 2300 °C. From cross-sectional images, scale non-adherence was noted as a limiting factor in oxidation resistance. The sample with the best scale adherence was HfB2–WSi2. Factors involving scale non-adherence such as vapor pressure, coefficient of thermal expansion mismatch and phase transformations were considered. In comparing the scale adherence of the samples it was hypothesized that vapor pressure buildup is the principal contributing factor in the scale adherence differences observed among the tested samples. However, the coefficient of thermal expansion mismatch and HfO2 phase transformation cannot be neglected as contributing factors to scale non-adherence in all samples.