Laser cladding of CoCrFeNi high-entropy alloy coatings: Compositional homogeneity towards improved corrosion resistance

Laser cladding of high-entropy alloy (HEA) coatings has aroused increasing attention in recent years. However, laser-cladded HEA coatings often suffer phase separation and/or elemental segregation, which may limit their full potential for corrosion resistance. In this study, CoCrFeNi HEA coatings were deposited on AISI 1045 steel substrate via laser cladding and then were subjected to post-annealing treatment. Microstructural characterization shows that a single-phase FCC structure forms in the laser-cladded CoCrFeNi HEA coating, without any phase separation. Columnar grains with cell substructures are dominating, with enrichment of Cr on cell walls and enrichment of Fe, Co, and Ni in cell interiors. Post-annealing promotes the recrystallization and the formation of equiaxed grained microstructures, and simultaneously erases the elemental segregation. Such homogenous elemental distributions lead to a higher corrosion potential and a lower corrosion current density, indicating an enhanced corrosion resistance. Such findings provide a guideline for fabricating highly corrosion-resistant HEA coatings for critical applications.