Plasma-sprayed Al–21Ti–23Cr coating for oxidation protection of TiAl alloys

To improve the oxidation resistance of the γ-based TiAl alloy, Al–Ti–Cr coatings approximately 150 μm in thickness were formed on Ti–48Al alloy using air plasma spraying process. The powder with the composition of Al–21Ti–23Cr (at.%) were used as an Al–Ti–Cr coating material. Isothermal and cyclic oxidation tests at 1000 °C in air were conducted to investigate the oxidation resistance of both Al–Ti–Cr coatings and of TiAl alloys with Al–Ti–Cr coatings. XRD performed the phase identification of Al–Ti–Cr coatings. After exposure at 1000 °C in air, rutile TiO2, which resulted from the oxidation of Ti during spraying, was always found in addition to α-Al2O3 in the oxide scale. However, isothermal and cyclic oxidation tests of a Ti–48Al alloy coated with an Al–Ti–Cr coating showed that this coating improved the oxidation resistance of TiAl alloy at 1000 °C. Furthermore, cyclic oxidation tests of Al–Ti–Cr coatings showed stable oxidation behavior at 1000 °C for up to 100 h because of a high level of adhesion between the coating layer and the oxide scale although the growth rate of the oxide was relatively high. Additionally, spark plasma sinterer treatment was introduced to reduce the porosity in the coating layer, so it could be suggested that the Al–21Ti–23Cr coating was effective in enhancing the oxidation resistance of the TiAl alloy at 1000 °C, although the porosity at coating/substrate interface must be reduced.