Microstructural characterization and high temperature oxidation kinetics of Ti-Al-C MAX phase-based coatings deposited by closed hollow cathode PVD on TiAl 48–2-2

This research investigates the fabrication of Ti-Al-C coatings containing MAX phases on TiAl 48–2-2 alloy using closed hollow cathode physical vapor deposition, with the aim of providing high-temperature oxidation protection at 850 °C. The resulting 12 μm thick coatings exhibit a columnar microstructure within which Ti₂AlC nanolaminates were identified by high resolution scanning transmission electron microscopy. These nanolaminates display basal planes aligned parallel to the growth direction at the core, with tilting observed in the sub-columnar regions. The coatings mainly consist of the Ti₂AlC and Ti₃AlC₂ MAX phases. The oxidation resistance of the coatings was evaluated using thermogravimetric analysis at 850 °C for 20 h in air, revealing a parabolic oxidation rate constant over five times lower than that of the uncoated substrate. Post-oxidation analysis identified the formation of a thin, continuous alumina scale approximately 320 nm thick, confirmed by high resolution transmission electron microscopy imaging to consist of a mixture of metastable θ-Al₂O₃ and stable α-Al₂O₃ phases. These findings demonstrate the effectiveness of Ti-Al-C coatings containing MAX phases in significantly enhancing the high-temperature oxidation resistance of TiAl alloys.