Investigation on the corrosion process of carbon steel coated by HVOFWC/Co cermets in neutral solution

The corrosion protection afforded to a carbon steel substrate by two cermet coatings (WC/12 wt.% Co and WC/17 wt.% Co; 0.05, 0.01 and 0.2 mm coating thickness), applied by high velocity oxygen fuel (HVOF) technique, has been studied in 3.5% NaCl solutions. Potentiodynamic polarization curves of cermet constituents, substrate and coated samples, iron and cobalt dissolution kinetics under potentiostatic conditions and galvanic coupling tests have been carried out. Cermet layer hinders the anodic process and WC/17%Co is more protective than WC/12%Co, particularly at high coating thickness. It is likely that the increase in the matrix cobalt content changes the pore morphology, from interconnected to isolated pores, with enhanced protective efficiency