Oxidation behavior of Nb–20Mo–15Si–5B–20Ti alloy in air from 700 to 1300 °C

Nb–20Mo–15Si–5B–20Ti alloy has been oxidized in air from 700 to 1300 °C for 24 h under static and cyclic oxidation modes. Linear and parabolic oxidation curves have been obtained at lower and higher oxidation temperatures. The two types of oxidation behavior may be related to the formation of a porous and dense oxide scales. Formation of these two distinct types of oxide scales has been experimentally verified. The oxide scale develops a three-layer structure at 1300 °C and the top layer consists of Nb2O5, TiO2, and SiO2. Ti concentration in α phase increases with increase in oxidation temperature resulting in the formation of Ti5Si3 in the microstructures in accordance with the calculated isotherms using Pandat™ software program. Amorphous SiO2 formed at higher oxidation temperatures provides an excellent oxidation resistance to this alloy. Thermal stresses developed by the oxides result in the formation of cracks between the oxides of the scale.