Oxidation of Zirconium Diboride with Tungsten Carbide Additions

The oxidation resistance of zirconium diboride (ZrB2) ceramics with tungsten carbide (WC) additions was studied. ZrB2 ceramics, nominally pure and with WC additions of 4, 5, and 6 mol%, were densified by pressureless sintering. During heating, the WC that was added to the ceramic dissolved into the ZrB2 matrix, forming a solid solution. Oxidation behavior was evaluated using isothermal furnace oxidation at 1500 degrees C and 1600 degrees C. The presence of tungsten reduced both the weight gain and oxide scale thickness compared with nominally pure ZrB2. After oxidation at 1600 degrees C for 3 h, the thickness of the ZrO2 outer scale was reduced from 4.7 mm for nominally pure ZrB2 to 0.5 mm for the ceramic containing 6 mol% WC. Analysis showed that WC additions improved the oxidation resistance of ZrB2 by changing the morphology of the zirconia scale formed during oxidation.