Structural and High-Temperature Oxidation Performance of Al-Co-Y Co-deposited Coatings on a TiAl-Nb Alloy at Low Temperatures

In this study, Al-Co-Y co-deposited coatings were prepared on a TiAl-Nb alloy through a pack cementation technique at temperatures ranging from 650 to 720 °C using NaF as the activator. The microstructures, formation processes, and high-temperature oxidation resistance of the optimized coating were investigated. The results indicated the formation of a dense and compact coating through a co-deposition process at 680 °C. This coating exhibited a characteristic structure consisting of an outer layer of TiAl₃, an inner layer of TiAl₂, and a thin Al-rich TiAl inter-diffusion layer. Additionally, the coating thickness exhibited a positive linear correlation with the square root of deposition time, following a linear relationship. High-temperature oxidation tests revealed that after 100 h of oxidation at 950 °C, the coating formed a dense oxide scale mainly composed of Al₂O₃ with a low TiO₂ content. The scale exhibited excellent high-temperature oxidation resistance. Moreover, the parabolic rate constant for the oxidation weight gain for the coating was approximately 8.1 × 10⁻³ mg²/cm⁴ h^1/2, which was significantly lower than that of the TiAl-Nb substrate by about two orders of magnitude.