Oxidation Resistance of Hafnium Diboride Ceramics with Additions of Silicon Carbide and Tungsten Boride or Tungsten Carbide

Dense samples of HfB2-SiC, HfB2-SiC-WC, and HfB2-SiC-WB were prepared by field-assisted sintering. The WB and WC additives were incorporated by solid solution into the HfB2 and the HfC that formed during sintering. Oxidation of the samples was studied using isothermal furnace oxidation between 1600 degrees and 2000 degrees C. Sample microstructure and chemistry before and after oxidation were analyzed by scanning electron microscopy and X-ray diffraction. The addition of WC and WB did not alter oxidation kinetics of the baseline HfB2-SiC composition below 1800 degrees C; however, at 2000 degrees C, HfB2-SiC-WC and HfB2-SiC-WB had oxide scales that were 30% thinner than the oxide scale of HfB2-SiC. It is believed that WC and WB promoted liquid-phase densification of the HfO2 scale, thereby reducing the path of oxygen ingress, during oxidation.