EFFECT OF SILICON AND NIOBIUM ON OXIDATION RESISTANCE OF TIAL INTERMETALLICS

The high temperature air oxidation of titanium aluminide intermetallics with small additions of silicon, niobium and a combination of silicon and niobium was studied in a temperature range between 973 and 1173 K. There was less weight gain when silicon and niobium were added individually. The combination of silicon and niobium resulted in much better oxidation resistance than the individual element additions. The effects of silicon and niobium on TiAl oxidation were different. For example, TiAl-Si showed a parabolic weight gain whereas TiAl-Nb did not. The surface oxide scale was basically composed of three layers, i.e. TiO, Al2O3 and TiO2 + Al2O3 from the surface inward. SiO2 was detected in the TiO2 + Al2O3 layer. Niobium strengthened the tendency to form Al2O3 in the early stage of oxidation, resulting in the formation of a continuous Al2O3 layer and a dense TiO2 + Al2O3 layer.