Effect of Y addition on microstructure and oxidation-resistant performance of Nb-Ti-Si based ultrahigh-temperature alloys

Nb-22Ti-15Si-5Cr-3Al-3Hf-xY (x=0, 0.03, 0.06, 0.12, 0.30 at%) alloy ingots were prepared by vacuum non-consumable arc melting, and then the alloys were oxidized at 1250℃ for 1, 10, 20 and 50 h, respectively. The effects of Y content on microstructure and oxidation behavior of the alloys had been studied. The results show that the addition of Y has less influence on the phase constituents of the alloy. The microstructure of the alloys is composed of Nbss and γ-(Nb,X)₅Si₃ phases. However, the eutectic microstructure is refined significantly due to the Y addition. The oxidation tests show that the scales of the alloys with different Y contents have similar phase constituents, mainly consisting of Nb₂O₅, TiO₂, Ti₂Nb₁₀O₂₉ and TiNb₂O₇. However, micro-holes and cracks in the scale as well as the mass gains per unit area of the alloy decrease with increasing Y contents in the alloys, indicating beneficial effects of Y additioin on the oxidation resistance of the alloy.