Enhanced Oxidation Resistance of ZrB₂-SiC-WC Composite below 1800 C

The effect of 3.6 vol% WC addition to ZrB2-20 vol% SiC (ZSW) on oxidation resistance is studied over a broad range of oxidation temperatures, 1000-1800 degrees C. Non-WC-containing samples (ZS) show significant surface damage and degradation during oxidation, losing protective B2O3 and SiO2-based surface layers and exposing a porous ZrO2 layer and base material for further oxidation. ZSW samples preserve their surface protective layers during oxidation up to 1800 degrees C while the underlying ZrO2 scale remains dense. The appearance of convection cells on the surface of ZSW samples during oxidation above 1600 degrees C is reported. This confirms the presence of boron-rich phases, suppressing oxygen permeation into the material and enhancing oxidation resistance of ZSW samples. During exposure of the samples to 1800 degrees C for 15 min, ZS and ZSW samples gain 11.1 +/- 1.5 and 7.8 +/- 0.3 mg cm(-2), respectively, due to oxidation. Exposure of the composites for 5 h at 1600 degrees C results in weight gains of 10.5 and 7.0 mg cm(-2) for ZS and ZSW samples, respectively. Cross sections of oxidized samples at 1800 degrees C show a tight zirconia layer below a glassy surface in ZSW and complete loss of surface glass in ZS, demonstrating the effectiveness of WC addition.