Interfacial strengthening and diffusion resistance mechanism of a fluorination-induced α-Al2O3 barrier in the TiAl/α-Al2O3/CrAlN system

Abstract

To mitigate detrimental interdiffusion at the TiAl/CrAlN interface, a compact α-Al₂O₃ diffusion barrier was developed on TiAl alloy via anodic fluorination and pre-oxidation. After 100 h of oxidation at 900 °C, the resulting α-Al₂O₃/CrAlN composite coating exhibits a mass gain of just 0.44± 0.03 mg cm^-2, only 55% of that of the CrAlN coating, underscoring its markedly superior oxidation resistance. The CrAlN top-coating serves as the primary oxidation barrier by forming a continuous (Al,Cr)₂O₃ scale. Meanwhile, the in-situ generated α-Al₂O₃ barrier establishes a semi-coherent interface with the Ti₃Al layer, ensuring excellent interfacial adhesion. More importantly, this barrier significantly suppresses bidirectional diffusion of Ti, Cr, and Al, thereby inhibiting the formation of an interdiffusion zone (IDZ) and secondary reaction zone (SRZ), which significantly extends the service life of the CrAlN coating. Furthermore, the α-Al₂O₃ interlayer, with its moderate thermal expansion coefficient, functions as a stress buffer to relieve interfacial thermal mismatch stresses.