Graphene-Reinforced WC-CoCr Coatings by High-Velocity Air Fuel Spraying: A Path to Superior Corrosion Protection

Abstract

The present study investigates the effect of graphene nanoplatelets (GNPs) on the microstructure and corrosion resistance of WC-CoCr coatings deposited via high-velocity air fuel (HVAF) spraying. The HVAF process effectively mitigated decarburization through its controlled lower combustion temperature. The addition of 1 wt.% and 2 wt.% GNPs markedly improved coating densification by filling nanoscale pores, thereby reducing porosity and achieving a relative density of 99.57% for WC-CoCr + 2G. The high thermal conductivity of GNPs enabled uniform heat dissipation during spraying, leading to a 9.7% reduction in crystallite size, and a 25.6% decrease in lattice strain. Electrochemical studies in 3.5 wt.% NaCl solution revealed a remarkable reduction in the corrosion rate, dropping from 4.27 × 10^–6 mpy for WC-CoCr to 1.71 × 10^–8 mpy for WC-CoCr + 2G, demonstrating an almost 99% improvement. The enhanced corrosion resistance is attributed to GNPs acting as a diffusion barrier against Cl⁻ and Na⁺ ions while simultaneously catalyzing the rapid formation of a protective Cr₂O₃ passivation layer. This novel insight into the functional role of GNPs in tuning microstructure, strain relaxation, and electrochemical stability establishes HVAF-sprayed GNP-reinforced WC-CoCr coatings as a transformative solution for high-performance corrosion protection in aggressive environments.