Enhanced oxidation resistance of laser-cladding TiAl composite coatings via Ti₂AlC MAX phase addition: Unraveling the underlying mechanism

The oxidation behaviors of Ti₂AlC MAX phase-reinforced TiAl-based composite coatings, fabricated on a TiAl alloy substrate via laser cladding, were thoroughly investigated. Special attention was paid to the underlying oxidation mechanism of the TiAl-based composite coatings containing Ti₂AlC. Results indicate that the incorporation of varying amounts of Ti₂AlC nanosheets leads to significantly microstructural evolution in terms of phase volume fraction and internal strain distribution. With increasing Ti₂AlC content, the oxidation mass gain decreases markedly after oxidation at 800 °C for 400 h. The oxidation rate of the coating with 10% Ti₂AlC addition is 50% and 84% lower than that of the coating with 5% Ti₂AlC addition and without Ti₂AlC addition, respectively. The corresponding oxidation mechanism involves the formation of a three-layer structure in the coating, consisting of TiO₂ and Al₂O₃ in the first layer, α₂-Ti₃Al and Al₂O₃ in the second layer, and a Cr-rich Laves phase in the third layer. The addition of Ti₂AlC increases the Ti/Al atomic ratio in the coating, promoting the formation of the α₂-Ti₃Al phase. Subsequent migration of Al and Cr facilitates the transformation of more α₂-Ti₃Al into a Laves phase, which effectively acts as a barrier to suppress further oxidation. This work not only provides essential insights into the high-temperature oxidation resistance mechanism of Ti₂AlC in TiAl-based composite coatings, but also offers scientific guidance for designing high-temperature oxidation-resistant coatings for TiAl alloys.