Synergistic effects of laser modification and Al film deposition on the oxidation resistance of NiCoCrAlY coatings

Laser modification can alter the surface roughness and microstructure to improve the oxidation resistance of NiCoCrAlY coatings. However, its effectiveness is often limited by Al depletion during processing. In this study, NiCoCrAlY coatings prepared by atmospheric plasma spraying (APS) were treated by laser remelting and Al film deposition (1 μm). The oxidation behavior of the Modified and Modified-Al coatings was comparatively investigated at 950 °C. Results showed that, although laser treatment introduced high-density dislocations and grain refinement to enhance atomic diffusion, Al depletion in the Modified coating promoted the early formation of mixed oxides (Al₂O₃, Cr₂O₃ and NiO). With extended exposure, competitive oxidation between Al and Cr led to a double-layer thermally grown oxide (TGO), with an Al₂O₃-rich upper layer and Cr₂O₃ lower layer, which cracked due to the poor thermal stability of Cr₂O₃. In contrast, the Modified-Al coating formed a dense, continuous Al₂O₃ scale throughout the entire oxidation process, with a thickness about half that of the Modified coating after 200 h of oxidation. These results demonstrate that Al film deposition significantly enhanced the oxidation resistance of Modified coatings.