Enhancing corrosion resistance in AlCrFeNiTi_x coatings via Ti-induced microstructural evolution and passive film optimization

AlCrFeNiTi_x high-entropy alloy (HEA) coatings with different Ti contents were fabricated by laser cladding and their phase evolution and corrosion resistance mechanisms were systematically investigated. The AlCrFeNiTi_x coatings exhibited superior corrosion resistance compared to the conventional AlCrFeNi coating. The incorporation of Ti promoted the formation of the L2₁ phase, transforming the microstructure into a sunflower-like microstructure, which hindered the initiation and propagation of localized pitting and reduces the pitting area of the passive film. The corrosion resistance of the coatings depended critically on the thickness and adhesion of the passive film. With increasing Ti content, the passivation film exhibited improved adhesion, and the AlCrFeNiTi_0.75 coating developed the thickest passive layer and exhibited the lowest corrosion current density, indicating optimal corrosion resistance. XPS analysis revealed that the synergistic effect of TiO₂ and Cr₂O₃ oxides in the passive film was critical for improving the corrosion resistance.