Effect of activator on the microstructure of Cr-Al-Y co-deposition coating and high-temperature wear resistance

Aiming at the problems of low hardness and easy wear of TiAl alloys at high temperatures, this study is dedicated to preparing a Cr-Al-Y diffusion coating on the surface of TiAl alloys to improve their high-temperature friction and wear properties. The Cr-Al-Y co-deposition coating was prepared on the surface of TiAlNb9 alloy using the pack cementation method at 1050℃ for 2 hours. The effects of activator type and content on the microstructure of the Cr-Al-Y co-deposition coating were analyzed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The tribological properties of the substrate and the co-deposition coating were evaluated under high-temperature conditions (600℃) against GCr15 balls, and the wear failure mechanisms were investigated. The experimental results of the co-deposition coating preparation revealed that the coatings prepared with different types and contents of activators exhibited a composite structure, consisting of an outer layer, an inner layer, and an interdiffusion zone. However, significant differences were observed in the thickness and density of the coatings. When 6 wt.% NH₄Cl was used as the catalyst, the co-deposition coating was approximately 30 μm thick, with the outer layer primarily composed of TiCr₂, TiCr, (Ti, Nb) Cr₄, and Ti₄Cr phases, the inner layer consisting of Ti₂Al phase, and the interdiffusion zone being a Nb-rich γ-TiAl phase. The structure of the co-deposition coating was dense, demonstrating the best performance. High-temperature friction and wear tests (against GCr15 balls at 600℃) showed that the Cr-Al-Y co-deposition coating reduced the friction coefficient of the TiAlNb9 alloy by approximately 45.8% and decreased the wear rate by about 97.6%, significantly enhancing the high-temperature wear resistance of the alloy. The wear mechanism of the TiAlNb9 alloy was identified as severe oxidative wear, adhesive wear, and abrasive wear, while the wear mechanism of the Cr-Al-Y co-deposition coating was primarily oxidative wear and adhesive wear. The improvement in wear resistance is attributed to the synergistic strengthening effect of the Cr₂O₃/Al₂O₃ mixed oxide film formed in the co-deposition coating. Overall, the preparation of Cr-Al-Y diffusion coatings on TiAl alloys via pack cementation effectively enhances the high-temperature wear resistance of the material surface, which provides a novel strategy for the surface coating preparation of TiAl alloys.