Electrochemical Investigations and Corrosion Behavior of HVOF WC-12Co Coatings Obtained from Powder and Aqueous Suspension

In our previous work, the potential of the suspension-HVOF spraying (S-HVOF) to produce dense-structured WC-12Co coatings has been shown. Significant work was devoted to the development of aqueous carbide suspensions starting from commercially available fine WC and Co raw powders feedstock.

This contribution proposes a comparative study of the corrosion properties of the S-HVOF WC-12Co coatings and conventional sprayed HVOF coatings. The corrosion properties were evaluated at room temperature 3 wt. % NaCl electrolytes with different pH values and in pH neutral 0.5 M Na₂SO₄ solution. By varying the pH value, the corrosion mechanism of the cermet coatings should be assessed more precisely, since the two components, WC and Co, show strongly different pH dependencies. The electrochemical properties of the sprayed coatings were investigated using open circuit potential measurements, linear sweep voltammetry and potentiodynamic polarization methods. Before and after corrosion tests, microstructural evaluations of the coatings were performed. Moreover, element analyses of the eluates have been performed to determine soluble corrosion products.

The S-HVOF coatings show a similarly good corrosion resistance as the conventional HVOF WC-Co coatings. Generally, the coating properties, i.e. microstructure and phase compositions, as well as the electrolyte significantly influence the corrosion performance of the sprayed coatings.