Oxidation behavior of CrAlN: ab initio molecular dynamics simulations and experiments

The high-temperature oxidation resistance of CrAlN coatings is synergistically regulated by aluminum content and temperature, but the atomic-scale mechanism of the initial oxidation stage remains unclear. This study combines ab initio molecular dynamics (AIMD) simulations with experiments to systematically investigate the effects of aluminum content (Cr_0.5Al_0.5N and Cr_0.15Al_0.85N) and temperature (773 K, 973 K, and 1173 K) on the oxidation mechanism of the coatings. Simulation results indicate that Cr_0.5Al_0.5N preferentially form a dense (Cr, Al)₂O₃ mixed oxide layer at high temperatures, with Cr–O–Al bonding dominating during the initial oxidation stage, effectively inhibiting oxygen diffusion, while in Cr_0.15Al_0.85N, aluminum atoms selectively migrate to form discontinuous Al₂O₃ layers, resulting in only a small amount of (Cr, Al)₂O₃ mixed oxide layers, thereby reducing the protective efficacy against oxidation. By analyzing the average displacement of oxygen atoms bonded to metal atoms (Cr, Al), it is found that high temperatures (1173 K) significantly accelerate metal atom migration, promoting the densification of mixed oxides in Cr_0.5Al_0.5N. At the same time, CrAlN-1 (Cr_0.54Al_0.46N) and CrAlN-2 (Cr_0.17Al_0.83N) coatings were prepared. The results indicate that at 1173 K (900 °C), CrAlN-1 forms a denser oxide layer of 0.3 μm primarily consisting of (Cr, Al)₂O₃, whereas CrAlN-2 develops a thicker oxide layer of 0.45 μm dominated by Al₂O₃ with minor (Cr, Al)₂O₃ content. The XPS analysis confirmed that as the temperature increased, the CrAlN-1 coating formed more Cr–O–Al bonds with better oxidation resistance. The experimental results are consistent with the simulation calculations, verifying the feasibility of predicting the anti-oxidation performance of coatings using ab initio molecular dynamics methods, and providing a theoretical basis for the design of high-performance CrAlN coatings.

Graphical abstract