Electrochemical Characterisation Study of Coatings Obtained by High Velocity Oxy-Fuel Spraying (HVOF)

The electrochemical behaviour of coated Cr3C2-NiCr steel in aerated 0.5 M H2SO4 solution was studied by means of electrochemical ac and dc measurements. The structural characterisation of the coated steel, before and after electrochemical tests, was also performed in order to identify the mechanism of the electrolyte penetration through the coating up to the steel substrate, causing its corrosion. This characterisation may also help to explain electrochemical results. Three types of Cr3C2-NiCr coatings performed by a High Velocity Oxy-Fuel Spraying system (HVOF) were analysed. The facility for the electrolyte penetration through the coating and the corresponding electrochemical behaviour of the samples were strongly influenced by the spray parameters used and heat treatment applied. It was observed that heat-treated coatings (Q1 and Q3) showed better corrosion resistance than the assprayed coating (A). For coatings Q1 and Q3, the electrolyte did not reach the steel substrate during the measurement, leading to a better protection of the steel substrate against corrosion.