Abstract
The microstructure and aqueous electrochemical corrosion characteristics of stainless steel 316L (UNS S31603) and nickel alloy 625 (UNS N06625) coatings deposited onto a carbon steel substrate using commercial high velocity oxyfuel (HVOF) spraying systems and a new high velocity wire flame spraying system were assessed. The electrochemical corrosion behaviour of the as prepared coatings was compared with their respective materials in wrought form. A HVOF sprayed coating of nickel alloy 625 was found to be more corrosion resistant in an aqueous saline environment than a coating of stainless steel 316L. However, the nickel alloy coating did not match the corrosion resistance of the same nickel alloy in wrought form, but may have the ability to offer corrosion resistance in saline aqueous environments approaching that of a wrought stainless steel. A porosity level of < 2.5% may not have a significant effect on the electrochemical activities of the HVOF sprayed coatings near the free corrosion (rest) potential. However, the level of oxidation depending upon the spraying system was shown to have an effect on the corrosion resistance of the sprayed coatings. The stainless steel and nickel alloy coatings produced using the high velocity wire flame spray system displayed much higher oxides compared with those produced using HVOF processes and. consequently, poorer corrosion resistance.
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