Corrosion behaviour of NiCrBSi plasma-sprayed coatings partially melted with laser

In this work, the effect of localised laser melting of NiCrBSi coatings, previously deposited by plasma spraying, on the corrosion behaviour was investigated. The microstructure of the coatings was analysed by scanning electron microscopy (SEM), with attached energy dispersive spectroscopy (EDS). Vickers microhardness profiles of the coatings were carried out. Their corrosion resistance was evaluated by potentiodynamic polarisation curves, polarisation resistance (Rp) and electrochemical impedance spectroscopy (EIS) measurements. The electrolytes used were 0.03 M NaCl, for all electrochemical tests, and a commercial organic lubricant, whose low conductivity limited the electrochemical study to EIS measurements.Laser treatment generates areas with a finer microstructure and, consequently, a higher hardness and improves the adherence between the coating and the substrate. From the electrochemical measurements in the NaCl solution can be deduced that localised laser melting of plasma-sprayed coatings does not affect their corrosion rate. Corrosion evolves due to a progressive penetration of the electrolyte through the pores and cracks formed during coating solidification. When the coating operates under uncontaminated organic lubrication conditions, the dissolution of the material is extremely slow. The contamination of this lubricant accelerates the degradation process of the coating.