Effect of Co on microstructure and high temperature oxidation resistance of Ti45Al-8Nb-0.3Y alloy

Ti45Al-8Nb-0.3Y-mCo (m=0, 0.5, 1, 2, atom fraction/%) alloys were prepared by vacuum arc non-consumable melting method. The microstructure and high temperature oxidation resistance of the alloys were investigated. The results show that the microstructure of TiAl-Nb alloy can be significantly refined by addition of Co element. However, Co can remarkably inhibit the formation of α2+γ lamellar while promote the formation of Co-rich B2 precipitations in the alloys. The oxide films formed on the Ti45Al-8Nb-0.3Y-mCo alloys mainly consist of relatively loose TiO2 and Al2O3 mixtures, after oxidation at 1000 ℃ for 100 h in air. With the increase of Co content, the mass gains of the TiAl-Nb-0.3Y alloys after oxidation increase obviously, while much better anti-spalling performance of the oxide films can be obtained. Addition of Co can reduce the internal stress of the oxide film to a certain extent, which is beneficial to the anti-spalling performance of the oxide film. However, the coarse B2 precipitation caused by Co weakens high temperature oxidation resistance of the alloy.