Optimizing the High-Temperature Oxidation Resistance of Nb-Si-Based Alloys by Adding Different Ti/Mo/Hf Elements

As a candidate material for turbine blades in aerospace engines, Nb-Si-based alloys have attracted significant research attention due to their high melting point and low density. However, their poor high-temperature oxidation resistance limits practical applications. Different alloying elements, including Ti, Mo, and Hf, were added to Nb-Si-based alloys to study the microstructural evolution of alloys. Additionally, the oxidation behavior and the oxidation kinetics of different alloys, as well as the morphology and microstructure of oxide scale and interior alloys at 1523 K from 1 h to 20 h were analyzed systematically. The current findings indicated that the Mo element is more conducive to promoting the formation of high-temperature precipitates of β-Nb5Si3 than the Ti and Hf elements. Inversely, the Ti element tends to cause the transition from high-temperature-phase β-Nb5Si3 to low-temperature-phase α-Nb5Si3, while the Hf element improves the appearance of the γ-Nb5Si3 phase but inhibits the other phases and refines the primary Nbss effectively. Noteworthily, compared with the oxidation weight gain of different alloys, Nb-16Si-20Ti-5Mo-3Hf-2Al-2Cr alloy has excellent high-temperature oxidation resistance, in which the oxidation products are TiNb2O7, Nb2O5, SiO2, TiO2, and HfO2. It can be determined that in the oxidation process, the Ti element will preferentially form an oxide film of TiO2, thereby wrapping around the matrix phases, protecting the matrix, and improving the antioxidant capacity, while the Hf element can form an infinite solid solution with the matrix and consume the small number of oxygen atoms entering the matrix, so as to achieve the effect of improving the oxidation resistance.