Exploration on the oxidation resistance of TiAlNbN films: Mechanisms of nanopore regulation and crack suppression

The high-temperature service environment places stringent demands on the oxidation resistance of traditional TiAlN films, which is, however, limited by severe poring and cracking on the oxidized surface. In this paper, the oxidation behavior and underlying mechanisms of the films following Nb alloying were systematically investigated through isothermal oxidation tests and density-functional theory (DFT) calculations. The results demonstrate that Nb addition effectively suppresses the anatase-to-rutile (a-TiO₂ → r-TiO₂) phase transformation, thereby preventing pore agglomeration. Furthermore, Nb regulates the diffusion kinetics of Al and Ti while occupying grain boundaries to impede elemental diffusion, collectively decelerating the oxidation rate and optimizing the stratified oxide structure. The optimized layer stratification alleviates the stress concentration inside the oxide layer by forming regular distribution of tiny holes, which avoids the generation of cracks and improves the long-term stability of the film. This work offers a comprehensive analysis into the internal mechanism of refractory element alloying on the oxidation behavior of TiAlN-based films.