Microstructures and Corrosion Behaviors of Laser Remelted High-Velocity Oxygen Fuel Sprayed Co-free Non-equiatomic Al_0.32CrFeTi_0.73Ni_1.50 High-Entropy Alloy Coating

Laser remelting of high-velocity oxygen fuel (HVOF) sprayed Co-free non-equiatomic high-entropy alloy (HEA) Al_0.32CrFeTi_0.73Ni_1.50 coating is carried out in an attempt to eliminate micropore defects on the original HVOF coating surface to improve the corrosion resistance under 3.5 wt.% sodium chloride solution. The influence of laser power adjustment on corrosion resistance is also discussed. At high laser power of 1500 W, the laser remelting coating is divided into two zones, namely the molten pool zone and the molten pool boundary zone. The molten pool zone coating structure is dense showing a BCC single-phase structure, and the interface is metallurgical bonding. Compared with the original BCC single-phase HVOF coating, the iron content of the molten pool zone coating is increased and the chromium content is relatively reduced, resulting in a decrease in corrosion resistance. Micropores rich in iron are formed in the molten pool boundary zone. Pitting occurs mainly at the micropores in the molten pool boundary zone, and galvanic corrosion between the molten pool zone and the molten pool boundary zone is formed to accelerate the expansion of pitting area in the molten pool boundary zone, while the molten pool zone as cathode is protected. The passivation film of the laser remelting coating at high laser power of 1500 W transforms into a PN-type double-layer structure from a P-type single-layer structure of the original HVOF coating. The laser power is adjusted down to a lower level to enhance corrosion resistance of coating. The laser remelting at a lower laser power can eliminate the pore defects of the molten pool boundary zone under high laser power and the original HVOF coating to obtain a denser coating. The laser remelting coating at a lower laser power is a BCC single-phase structure. The laser remelting coating forms a double-layer structure, that is, the inner layer is the HVOF coating and the outer layer is the laser remelting coating. The double-layer structure eliminates the iron element transport from the substrate to the laser remelting coating. The passive film of the laser remelting coating at a lower laser power is a P-type single-layer structure as same as that of the original HVOF coating.Please check if the corresponding author affiliation is correctly identified.Yes,  the corresponding author affiliation is correctly identified.