Static and Cyclic Oxidation of Ti–44Al and Ti–44Al–xNb Alloys

Binary, Ti–44Al, and ternary, Ti–44Al–xNb (x=4, 8, and 11) alloys were subjected to static and cyclic oxidation in air up to a period of 1 week at 850 and 950°C. The oxidation behavior is characterized by plotting a graph between weight gain as a function of time or number of cycles. The binary alloy undergoes the most severe oxidation while Nb provides resistance to oxidation, which increases with an increase in concentration. Oxides were examined by SEM and EDX was used to perform chemical analysis. Alternate oxide layers rich in alumina and titania were found along with an aluminum-depleted zone underneath the oxide scale. Different microstructures were observed for the alloys subjected to static- and cyclic-heating modes. Defects like twins and stacking faults were generated after a static mode of heating, while transformation products at the grain boundaries dominate the microstructures for samples subjected to cyclic heating.