Oxidation resistance of powder compacts of the Nb–Si–Cr system and Nb3Si5Al2 matrix compacts prepared by spark plasma sintering

Powder compacts with several different compositions of the Nb–Si–Cr system and Nb3Al2Si5 matrix compacts with a composition of Nb–47Si–20Al (at.%) were prepared by spark plasma sintering. The microstructure, oxidation behavior and mechanical and physical properties of each compact were investigated. Adding more than 10 at.% Cr to NbSi2 compacts greatly improved their poor oxidation resistance at 1023 K. However, the oxidation resistance of such Cr-added compacts was poor at 1573 K because of volatilization of Cr oxide formed on their surface and fast growth of the oxidized layer. Nb3Si5Al2 matrix compacts with a composition of Nb–47Si–20Al showed extremely good oxidation resistance at 1373–1573 K because thin protective Al2O3 scale was formed. Nb3Si5Al2 matrix compacts partially melted at temperatures between 1873 and 1973 K. Nb3Si5Al2 single-phase ingots were not obtained by arc melting.