COMPARISON OF THE OXIDATION PROTECTION OF HfB_2 BASED ULTRA-HIGH TEMPERATURE CERAMICS BY THE ADDITION OF SiC OR MoSi_2

摘要

Oxidation resistance tests were conducted on HfB_2-SiC and HfB_2-MoSi_2 samples using direct electrical resistance heating at 1750, 1950 and 2490℃. Analysis of the formed oxide scales showed a distinct difference between the two silicon bearing additives to HfB_2. SiC formed a layered oxide scale of HfO_2 and SiO_2, offering oxidation protection at 1750℃ and a non-adherent scale at 1950℃. MoSi_2 promotes a mixed scale of SiO_2, HfO_2, and molybdenum oxides and borides at all temperatures that remained adherent to the bulk up to 2490℃. Comparison and evaluation of oxide scales showed the improved adherence performance of HfB_2-MoSi_2 when compared to HfB_2-SiC.