1997 Volume 46 Issue 7 Pages 449-455
Although TiAl has a great potential as future high temperature materials because of a good strength-to-weight ratio even at high temperature, it is not highly resistive against oxidation at high temperature. The oxidation behavior of Ti-Al intermetallic compounds (Ti-34%Al and Ti-37%Al) has been studied at 1173K and 1273K in Ar-20%O2 and in N2-20%O2 under atmospheric pressure. The microstructures of the specimens were controlled by heat treatment and/or isothermal forging. Mass gain of TiAl by oxidation in Ar-20% O2 was much smaller than that in N2-20%O2 in all cases. XPS analysis also showed the remarkable influence of nitrogen on the structure and composition of oxide layers. Titanium nitride was formed at the interface between oxidized surface and substrate at the initial stage of oxidation under N2-20%O2 atmosphere, resulted in the suppression of the formation of the continuous Al2O3 layer. Therefore, the oxidation of TiAl in N2-20%O2 was accelerated compared with that in Ar-20%O2. A model of the oxide layer growth is proposed to explain the role of nitrogen in the oxidation process.
