Oxidation behavior and mechanical properties of a directionally solidified high Nb TiAl based alloy between 800 °C and 900 °C

The high temperature oxidation behavior and mechanical property response of a directionally solidified Ti-46Al-7Nb-0.4W-0.6Cr-0.1B alloy were investigated. The ultimate tensile strength of the alloy at 800 °C, 850 °C and 900 °C are 647 MPa, 590 MPa and 508 MPa, respectively, and the tensile fracture mode changed from brittle cleavage fracture to micro-void accumulation ductile fracture. At lower temperatures Al₂O₃ forms first, growing along the γ lamellae to form oxide bands aligned with the lamellar orientation. The oxidation mass gain of the alloy after 900 °C/100 h isothermal oxidation is only 0.91 mg/cm². The oxidation kinetics results show the microalloyed high Nb TiAl alloy has excellent oxidation resistance, which is due to the formation of a TiO₂ layer containing Nb, Cr and W, the AlNb₂ phase and an Al/Cr rich transition layer above the directionally solidified lamellar matrix.