Corrosion behaviour of HVOF-sprayed Co-Cr-W-C coating in NaCl solution.

Stellite 6 (Co-Cr-W-C) coating was deposited on carbon steel substrate by high-velocity oxyfuel spraying. The electrochemical corrosion behaviour of the coatings was investigated in 3.5% NaCl solutions at 25°C by means of polarisation studies and electrochemical impedance spectroscopy (EIS) measurements. The immersion time before corrosion tests was 0.5 and 24 h. The results showed that the corrosion rate of the coatings was lower than that of the steel substrate by one order of magnitude. An active-passive behaviour was observed during anodic polarisation of the coatings at both immersion times. The degree of substrate attack after polarisation tests of coated samples was not considerable. EIS measurement showed that two-time constants were observed in Nyquist plots of the coatings. [ABSTRACT FROM AUTHOR]