Composition optimisation and electrochemical corrosion behaviour of flame-sprayed FeCoCrNiAlx high-entropy alloy coatings

This study reports on the fabrication of FeCoCrNiAlx (x = 0, 0.5, 1, and 2) high-entropy alloy coatings via high-velocity oxy-fuel (HVOF). The microstructure, wear resistance, and corrosion resistance of the coatings were investigated as a function of Al content. The results revealed that the addition of Al induced a phase transition, transforming the coatings from a single face-centered cubic (FCC) structure to a dual-phase FCC and body-centered cubic (BCC) structure. Notably, the dual-phase in the FeCoCrNiAl1 coating exhibited the best stable coexistence. At room temperature, the phase transition and lattice distortion caused by Al incorporation led to both increased hardness and a lower average coefficient of friction for the coatings. In 3.5 wt% NaCl solution, with increasing Al content, the corrosion potential of the coatings first rose and then fell, whereas the corrosion current density first declined and then rose. The FeCoCrNiAl1 coating, in particular, demonstrated superior corrosion resistance. This was attributed to the synergistic effects of its stable dual-phase structure, relatively smooth surface morphology, and the formation of a stable corrosion product film, which resulted from the optimal Al addition. Consequently, this coating achieved an optimal combination of mechanical properties and corrosion resistance.