Corrosion Behaviour of HVOF-Sprayed CoCrNi Coating on Copper Alloy Surface in NaCl Solution

To reduce the corrosion degradation of copper alloys, an equiatomic CoCrNi medium-entropy alloy (MEA) coating was successfully fabricated on a copper alloy plate using high-velocity oxygen-fuel (HVOF) spraying. The microstructure, corrosion behaviour, and passive film characteristics of the CoCrNi MEA coating in a 3.5 wt.% NaCl solution were investigated. The CoCrNi MEA coating mainly consisted of a face-centred cubic solid solution structure and a small amount of metal oxide. Compared to that of the widely used electroplated NiCo coating, the corrosion current density of the CoCrNi MEA coating dropped by 93%. The pitting corrosion of the CoCrNi MEA coating originated from the interface between the solid solution matrix and the oxide. Due to the strong protective passive film and low coincident site lattice boundaries, the CoCrNi MEA coating exhibited superior corrosion resistance in a NaCl solution.