Investigating the thermal oxidation behavior of Ti-6Al-7Nb alloy in dry air

摘要

The thermal oxidation behavior of a forged Ti-6Al-7Nb (Ti67) alloy was investigated in dry air conditions. The alloy specimens were oxidized for 50 h at different temperatures (650 degrees C, 750 degrees C, and 850 degrees C) and the oxidation kinetics were analyzed. The microstructure of Ti67 after oxidation and the different phases and compounds were identified. A parabolic equation based on weight gain was used to define the oxidation rate. The parabolic rate constant increased from 1.10 x 10(-8) at 650 degrees C to 2.10 x 10(-8) and 1.53 x 10(-7) g(2)/(cm(4)center dot h) at 750 degrees C and 850 degrees C, respectively. At 650 degrees C, the oxidation behavior resumed the parabolic behavior until 40 h, a breakaway phenomenon. At 750 degrees C, a linear behavior was observed in the periods of 20-50 h. This linear trend appeared also after 35-50 h at 850 degrees C. The activation energy was found to be 238.4 kJ/mole. At the lowest oxidation temperature (650 degrees C), a disconnected oxide layer was observed. These variations in the response of Ti67 alloy to the different thermal oxidation conditions are worthy of consideration when modifying the surfaces for biomedical applications.