Flow-interface-reaction interaction governing synergistic erosion-corrosion of WC-4Co-58Cr coating under rotating liquid-solid flow in marine environment

The hydraulic machinery in marine environment is vulnerable to the synergistic damage by high-speed rotating flow, chloride-induced corrosion, and sand particle erosion, which has become the major threat to its safe and efficient operation. In this study, the erosion-corrosion behavior of HVOF-sprayed WC-4Co-58Cr coating is investigated in artificial seawater containing 3.5 wt% quartz sand with an average particle size of about 400 μm at 25 °C. The flow velocity ranges from 3 to 9 m/s. Based on the coupling analysis of multi-component weight loss, electrochemical behavior and micro-damage morphology, the multi-scale coupling process of fluid flow, particle-surface impact, ion mass transfer and interface electrochemistry is revealed. The results show that the erosion-corrosion mechanism transfers with the flow velocity. At low velocities, corrosion is the dominant factor in material degradation. At 3 m/s, the total loss rate is 0.069 mm/y, in which pure corrosion accounts for 46.38% of the total damage, while the synergistic component contributes 37.68%. As the velocity increases, the synergistic effect intensifies and eventually becomes the dominant damage mechanism. At 9 m/s, the total loss rate increases to 0.310 mm/y, and the synergistic component reaches 47.42%. In particular, the corrosion-accelerated erosion component accounts for 28.39%. This transition stems from turbulent shear stress enhancing the mass transfer of corrosive medium, combined with localized breakdown of the passive film due to high-speed particle impact. Their interaction creates a positive feedback mechanism. The WC-4Co-58Cr coating with high Cr content forms a composite protective film primarily composed of Cr₂O₃, enriched with hydroxyl compounds on the outer layer, demonstrating strong resistance to synergistic erosion-corrosion. The study elucidates the intrinsic relationship among hydrodynamic effects, particle impact behavior, ion mass transfer processes, and material damage evolution, which contributes to the optimal design of erosion-corrosion resistant materials based on flow-induced damage mechanisms.