Microstructural evolution and corrosion resistance of CoCuNiTiX0.6 (X = Mn, Al) HEA coatings on the 45-steel substrate

Laser cladding technology was employed to prepare dual-phase CoCuNiTiX 0.6 (X = Mn, Al) HEA coatings on the 45-steel substrate. The phase structure, microstructural evolution, composition analysis, and corrosion resistance of CoCuNiTiX 0.6 (X = Mn, Al) HEA coatings were studied using an X-ray diffractometer, OM, SEM, EDS, and ECW. The results demonstrate that CoCuNiTiMn 0.6 alloy consists of an FCC primary phase and a BCC phase. After replacing Mn with Al, CoCuNiTiAl 0.6 alloy transforms into a structure dominated by the BCC phase, with a minor amount of the FCC phase. The lattice constants and cell volumes of BCC and FCC in Al-containing alloy are relatively large, but their densities are low. Both alloys have dendritic structures. The high viscosity and poor fluidity of Mn-containing alloy melt increase atomic diffusion resistance and a relatively slow occurrence of “composition undercooling” during solidification, resulting in coarse columnar crystals and pore defects. Ti and Cu exhibit the highest concentrations in the primary phase and interdendrite regions, respectively. The composition differences of Ni, Mn, and Al in different regions are relatively small. Both alloys show obvious passivation zones in 3.5wt% NaCl solution, and their Nyquist plots present a flattened semi-circular arc. The capacitive arc radius, maximum phase angle, and m value of CoCuNiTiAl 0.6 HEAC are relatively large, indicating that its corrosion resistance is relatively superior, mainly due to its dense passivation film, fewer defects, and relatively uniform composition distribution.