Oxidation behavior of Nb-Ti-Si base multielement alloys at 1250°C

The Nb-22Ti-16Si-6Cr-3Al-4Hf-1.5B-0.06Y (atomic fraction, %) alloy ingot was prepared by vacuum consumable arc melting. The oxidations were conducted at 1250°C for 5, 10, 20, 50 and 100 h, respectively. X-ray diffraction (XRD) was used to identify the phases presented in the oxide scales and alloy substrate. Cross sections of the oxidation specimens were observed by scanning electron microscopy (SEM) and the chemical compositions of constituent phases were analyzed using EDS. The results show that the constituent phases of the oxide scale for the sample oxidized for 5 h were SiO₂, TiO₂, Nb₂O₅, Ti₂Nb₁₀O₂₉ and TiNb₂O₇. As the oxidation prolonged, the solid solution reaction took place among the oxides in the scales and the content of Nb₂O₅ and Ti₂Nb₁₀O₂₉ reduced, but the content of TiNb₂O₇ increased. The EDS analysis showed that a large quantity of TiO_x and HfO₂ formed within alloy matrix. TiO_x distributed mainly at the interfaces between (Nb, Ti)₅Si₃ and Nb_ss, and HfO₂ with needle-like morphologies distributed in (Nb, Ti)₅Si₃ blocks. There are some bulk HfO₂ presented after oxidation for 50 at the interfaces between (Nb, Ti)₅Si₃ and Nb_ss.