Microstructural evolution and corrosion behavior of CoCrFeNiAlxMn(1−x) dual-phase high-entropy alloy coatings prepared by laser cladding

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CoCrFeNiAlxMn(1−x) (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) high-entropy alloy (HEA) coatings were prepared on the surface of AISI 1045 steel via laser cladding technology. The microstructural evolution and corrosion resistance of the coatings have been systematically studied. The results showed that the crystalline structure of the HEA coatings changed from a single FCC solid-solution to dual-phase of FCC+BCC solid-solution, and eventually to a single BCC solid-solution, with the gradual increase of x. The decrease in the ratio of FCC phase to BCC phase volume fraction with increasing of x indicated that Al element had a stronger effect to form BCC phase than Mn element. The corrosion resistance of CoCrFeNiAlxMn(1−x) HEA coatings was quantitatively analyzed by fitting equivalent circuit and calculating electrochemical parameters. For the dual-phase HEA coatings (x = 0.2 to 0.8), the coating had the best corrosion resistance with maximum impedance (25,016.228 Ω/cm2) and the minimum corrosion rate (0.0464 g/m2h) when x = 0.8. This was due to the fact that the passive film became stable and had stronger self-repair ability with x increasing from 0.2 to 0.8. The passive film was mainly identified as Al2O3, Co3O4, Cr2O3, Fe2O3, Fe3O4, and a small amount of Mn2O3. With the gradual increasing of x, the dominant corrosion mechanism changed from pitting corrosion to dual-phase corrosion. The mechanisms of pitting corrosion and dual-phase corrosion were analyzed in detail.