Regulating TGO Nucleation and Growth of M CrAl X Coatings via Femtosecond Laser Remelting: The Role of Reactive Elements in the Oxidation Resistance

ABSTRACT M CrAl X coatings are widely used as bond coats in thermal barrier coating systems to protect turbine blades from high‐temperature oxidation. However, their oxidation resistance is often restricted by uncontrolled microstructures, surface roughness, and aggregation of reactive elements (REs). In this study, high‐repetition‐rate femtosecond laser remelting (HRR‐FLR) is introduced as an advanced surface modification technique to overcome these limitations. Owing to its ultrafast self‐quenching and polishing effects, HRR‐FLR enables precise control of surface morphology, microstructural reconstruction, and REs redistribution. As a result, a uniform and periodic distribution of REs is achieved, which promotes the rapid nucleation and compact growth of α‐Al 2 O 3 and helps maintain the stability of the oxide scale under long‐term exposure. The HRR‐FLR‐treated coatings show remarkable performance, with the TGO growth rate reduced by approximately 80% and the oxidation lifetime extended to about 300 h compared with the untreated ones. Moreover, REs exhibit a dual function during oxidation: They act as preferential nucleation sites for Al 2 O 3 in the initial stage and segregate at TGO grain boundaries during growth, thereby suppressing outward cation diffusion. Overall, HRR‐FLR provides a novel and effective femtosecond‐laser‐based approach to tailor REs’ behavior and enhance the long‐term oxidation resistance of M CrAl X coatings, offering practical insights for the design of high‐temperature protective systems.