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

Abstract The oxidation behaviour of an intermetallic alloy, Ti–46.7Al–1.9W–0.5Si, was studied in air and Ar–20%O 2 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%O 2 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%O 2 atmosphere at 950 °C. Higher oxidation rates were observed in air than in Ar–20%O 2 at all three experimental temperatures. Multi-layered scales developed in both environments. The scale formed in air consisted of TiO 2 /Al 2 O 3 /TiO 2 /TiN/TiAl 2 layers, ranging from the surface to the substrate—whilst the scale developed in the Ar–20%O 2 atmosphere comprised of the sequence TiO 2 /Al 2 O 3 /TiO 2 /Al 2 O 3 /Ti 3 Al/substrate. The two layers of Al 2 O 3 in Ar–20%O 2 were more effective in providing protection of the substrate against high temperature corrosion than the single layer of Al 2 O 3 formed in air.