High temperature oxidation behaviors of Ti-22Al-25Nb Alloy Prepared by Reactive Sintering with Element Powders

Abstract:

Ti-22Al-25Nb is a high-temperature structural material which oxidation resistance will be important for further developments and applications. The oxidation behaviors of sintered Ti-22Al-25Nb alloy which was prepared by reactive sintering with element powders were investigated at the temperature range of 650~950 °C in static air. The maxima of the mass gains at different temperatures (650 °C, 750 °C, 850 °C, 950 °C) were 0.15 mg·cm?2, 0.41 mg·cm?2, 1.68 mg·cm?2 and 6.9 mg·cm?2, respectively. The Ti-22Al-25Nb sintered alloy exhibited a good oxidation resistance, especially below 750 °C (with breakaway oxidation occurring at 950 °C). According to the oxidation kinetics analyses, the oxidation behaviors approximately followed parabolic law below 750 °C. Whereas, with temperatures rising above 850 °C, the oxidation behaviors fitted linear law. Oxidation kinetics were discussed with regard to the influence of the Nb alloying element. Based on the observations and analyses of the oxidation morphologies and phases, there were proven that the oxidation resistance of the O phase (orthorhombic Ti2AlNb) was superior to others. The reason for this phenomenon was the difference of Nb content in different phases could result in a difference of oxidation resistance.

Key words:Ti-22Al-25Nb sintered alloy; orthorhombic phase; high-temperature oxidation; oxidation mechanism