Oxidation behaviour of Ti-46.7Al-1.9W-0.5Si in air and Ar-20%O_2 between 750 and 950℃

摘要

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℃. Oxidation of the alloy followed a parabolic rate law at low temperature (750℃) in both environments. The alloy oxidised parabolically in air and at a slower rate in Ar-20%O_2 at 850 ℃. Following a parabolic oxidation for a relatively short exposure period (72 h) at 950 ℃, 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 ℃. 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/Al2O_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_2O_3 /TiO_2/Al_2O_3 /Ti_3Al/substrate. The two layers of Al_2O_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_2O_3 formed in air.