High temperature oxidation behaviour of Nb and HfO2 coatings on ZrB2

Abstract

ZrB2 has a unique combination of properties such as high melting point (>3000°C) and low theoretical density, high strength and elastic modulus which makes itself a very attractive candidate for ultra-high temperature applications. However, its’ oxidation resistance is poor above 800°C which limits its application for aero-propulsion and hypersonic flight applications. Few studies have shown that the addition of transition metals into the ZrB2 material could improve the oxidation behaviour at high temperatures. In this study, two different materials were applied as oxidation protective coatings by means of magnetron sputtering technique on top of ZrB2 : the transition metal Nb and HfO2. The oxidation studies were performed at 1500 and 1600°C in a box furnace under synthetic air atmosphere for different times. Both coatings have shown promising results and the ZrO2 scale growth was drastically reduced. Formation of mixed oxides comprising of Nb and ZrO2 at the surface has reduced the oxygen transport at the ZrB2 reaction front. Similarly, HfO2 has acted as a barrier to the oxygen transport and a lower oxidation rate was achieved.