Comparison of the Oxidation Protection of HfB 2 Based Ultra‐High Temperature Ceramics by the Addition of SiC or MoSi 2 .

Oxidation resistance tests were conducted on HfB2-SiC and HfB2-MoSi2 samples using direct electrical resistance heating at 1750, 1950 and 2490°C. Analysis of the formed oxide scales showed a distinct difference between the two silicon bearing additives to HfB2. SiC formed a layered oxide scale of HfO2 and SiO2, offering oxidation protection at 1750°C and a nonadherent scale at 1950°C. MoSi2 promotes a mixed scale of SiO2, HfO2, and molybdenum oxides and borides at all temperatures that remained adherent to the bulk up to 2490°C. Comparison and evaluation of oxide scales showed the improved adherence performance of HfB2-MoSi2 when compared to HfB2-SiC.