Oxidation behaviour of Ti-46.7Al-1.9W-0.5Si in air and Ar-20%O2 between 750 and 950 °C

The oxidation behaviour of an intermetallic alloy, Ti-46.7Al-1.9W-0.5Si, was studied in air and Ar-20%O2 atmospheres at 750, 850 and 950 °C. Oxidation of the alloy followed a parabolic rate law at low temperature (750 °C) in both environments. The alloy oxidised parabolically in air and at a slower rate in Ar-20%O2 at 850 °C. Following a parabolic oxidation for a relatively short exposure period (72 h) at 950 °C, the oxidation rate was reduced after prolonged exposure (up to 240 h) in air. The alloy oxidised in a slower manner in the Ar-20%O2 atmosphere at 950 °C. Higher oxidation rates were observed in air than in Ar-20%O2 at all three experimental temperatures. Multi-layered scales developed in both environments. The scale formed in air consisted of TiO2/Al2O3/TiO2/TiN/TiAl2 layers, ranging from the surface to the substrate-whilst the scale developed in the Ar-20%O2 atmosphere comprised of the sequence TiO2/Al2O3/TiO2/Al2O3/Ti3Al/substrate. The two layers of Al2O3 in Ar-20%O2 were more effective in providing protection of the substrate against high temperature corrosion than the single layer of Al2O3 formed in air.