Improved Oxidation Resistance of Zirconium Diboride by Tungsten Carbide Additions

The effect of tungsten carbide (WC) additions on the oxidation resistance of zirconium diboride (ZrB2) was studied. Zirconium diboride ceramics, nominally pure and with the addition of 4 mol% WC, were densified by pressureless sintering. During densification, the WC that was added to the ceramic dissolved into the ZrB2 matrix, forming a solid solution. Oxidation behavior was evaluated using thermal gravimetric analysis up to 1500 degrees C and isothermal furnace oxidation at 1500 degrees and 1600 degrees C. The WC additions reduced both the weight gain and the oxide scale thickness. After oxidation at 1600 degrees C for 3 h, the mass gain decreased from 22 mg/cm(2) for nominally pure ZrB2 to 8 mg/cm(2) for the WC-containing ceramic. Analysis showed that the WC additions improved the oxidation resistance of ZrB2 by promoting densification of the zirconia scale formed during oxidation through liquid-phase sintering.