William G. Fahrenholtz

Oxidation of ZrB2 and ZrB2-SiC Ceramics with Tungsten Additions

Abstract : The effect of tungsten additions on the oxidation behavior of zirconium diboride-based ceramics was studied. Four mole percent tungsten carbide was added to ZrB2. The oxidation behavior was studied using thermal gravimetric analysis and isothermal testing in flowing air. Upon heating to 1500 degrees C, the mass gain decreased from approx. 14 milligrams/(square centimeter) for nominally pure ZrB2 to approx. 4.5 milligrams/(square centimeter) for tungsten containing ZrB2. After heating to 1500 degrees C for three hours, the scale thickness on nominally pure ZrB2 was approx. 500 micrometers compared to approx. 100 micrometers for tungsten containing ZrB2. Tungsten additions improved the oxidation resistance of ZrB2 by modifying the morphology of the ZrO2 scale by liquid phase sintering, making it a better barrier to oxygen diffusion.