High temperature oxidation behaviour of Ti3Al-Nb intermetallics

The oxidation behaviour of (alpha(2)-Ti3Al base alloys: Ti-25Al-11Nb, Ti-24Al-20Nb and Ti-22Al-20Nb was investigated in the present work. The alloys were used in as-received condition and after heat-treatment: 1060 degrees C, 4 hr., followed by air cooling and furnace cooling. The oxidation tests were done at 800 and 900 degrees C in air. At both the temperatures, kinetics were parabolic for the alloy, Ti-25Al-11Nb, while Ti-24Al-20Nb and Ti-22A1-20Nb showed nonparabolic kinetics with much higher oxidation rates. The massive spallation of the scale was observed at 900 degrees C for these two alloys. The analysis of the oxide scale, using SEM/EDAX and XRD, confirmed the scale to be a mixture of TiO2, Al2O3 With some Nb2O5. In situ oxidation analysis by AES confirmed that the initial growth was of titania based scale. The effect of variation of Al and Nb content on the oxidation behaviour is discussed.