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-46Al7Nb-0.4W-0.6Cr-0.1B alloy were investigated. The ultimate tensile strength of the alloy at 800 degrees C, 850 degrees C and 900 degrees 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 gamma lamellae to form oxide bands aligned with the lamellar orientation. The oxidation mass gain of the alloy after 900 degrees 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.