Flow-accelerated corrosion mechanism of overlap and non-overlap zones in multi-track laser-clad nickel-based alloy coating

A large-area laser-clad coating was realized by overlapping laser tracks and thus presents overlap and non-overlap zones on the surface. The microstructure and corrosion behaviors of the overlap and non-overlap zones of the multi-track laser-clad nickel-based alloy coating at various flow rates and impact angles were investigated. Results indicated that overlap zone presented coarse columnar dendrites rather than cellular structures. The primary phases were mainly composed of γ-Ni, and the precipitation at the grain boundary was Ni₆Mo₆C. At the impact angle of 60° and flow rate of 6 m/s, overlap zone showed 2.0 × 10^–7 A/cm² higher stable potentiostatic polarization current density at passivation film destruction and furrow formation than non-overlap zone. The increase content of Mo^x+ (Mo) in non-overlap zone was 4.38% more than that in overlap zone after corrosion indicating the better Cl⁻ corrosion resistance. The current densities increased with the enhanced flow rate. At the impact angle of 60°, the flow rate increased from 1 to 6 m/s, and the potentiostatic current density increased by 3.0 × 10^–7–3.7 × 10^–7 A/cm². With the increase of the impact angle, the stable current densities increased first and then decreased. And the surface morphology changed from long and shallow ravines to short deep gully.