Oxidation Behavior of Ti3Al–xNb (x=0, 3, 7, 11, 13 at%) at 1073–1273 K in Air

Titanium aluminide (Ti 3 Al-Nb) has potential for high temperature applications because of its low density and high temperature strength. The isothermal oxidation behavior of Ti 3 Al containing 3-13 at%Nb was investigated in air over the temperature range of 1073-1273 K using thermogravimetric analysis. Oxide products were identified using X-ray diffraction and energy dispersive x-ray analysis. Surface morphology of oxide scales and cross-sections of oxidizied specimens were examined using scanning electron microscopy. At 1073 K, the difference of the mass gain between Nb-free Ti 3 Al and Nb containing Ti 3 Al is not very obvious. However, the remarkable decrease in oxidation rates was observed for Ti 3 Al-11Nb and Ti 3 Al-13Nb alloys at 1173 and 1273 K. The oxide scales of Ti 3 Al-11Nb and Ti 3 Al-13Nb were compact and multilayered, and consisted primarily of TiO 2 doped with Nb, and a layer of Al 2 O 3 . For Ti 3 Al, the oxide layer consisted of pillar-like TiO 2 and was porous. A Nb-rich layer was found adjacent to the substrate for Nb containing Ti 3 Al alloys.