Oxidation behavior of Nb coatings on ZrB2

Abstract

The demand for more efficient materials at elevated temerpatures is ever-increasing and the availability of such materials is scarce. ZrB2 is a member of the family of Ultra High-Temperature Ceramics (UHTCs). ZrB2 has unusual properties such as extremly high melting point, strenght, thermal conductivity, elastic modulus and a low theoretical density, which makes itself very attractive for applications in hypersonic vehicles, aero-propulsion and more. However, the oxidation properties above 1500°C limits the use of ZrB2 under oxidizing conditions. Various studies have shown that the addition of transition metals improves the oxidation behavior of ZrB2 at higher temperatures. This approach can comprise the mechanical and thermal properties of the resulting ceramics. This study focuses on the application of Nb metallic coatings by means of magnetron sputtering to improve the oxidation resistance of ZrB2. The oxidation studies were performed at 1500°C in a tube furnace under different atmospheres for 1h, 4h, and 10h exposure times. The influence of a pre-annealing (under vacuum) on oxidation behavior was also investigated. The Nb metallic coatings have shown promising results and reduced the oxide scale growth compared to uncoated ZrB2. The formation of mixed Nb and Zr oxides at the surface has reduced the oxygen transport at the ZrB2 reaction font by grain refinement. The pre-annealing improved the beneficial effects of the coatings.