Electrochemical comparison between corrosion resistance of some thermally sprayed coatings

Electrochemical polarisation and impedance spectroscopy tests in0.1 M HCl and 0.1 M H2SO4 solutions were performed on HVOF-sprayedcermet coatings (WC–17% Co, WC–10% Co–4% Cr) and AtmosphericPlasma-Sprayed (APS) ceramics (Al2O3, Al2O3–13 wt%TiO2, Cr2O3) with APSbond coat (Ni–Co–Cr–Al–Y). Reference tests were also performed on hardchrome electroplating. Plasma-sprayed coatings offer limited substrateprotection owing to interconnected porosity, although the bond coat promotessome forms of passivation in H2SO4. HVOF-sprayed cermets possess goodcorrosion resistance in both environments. Chrome electroplating showscomparatively better corrosion resistance in H2SO4, but worse in HCl.