Comparative study of corrosion performance of HVOF-sprayed coatings produced using conventional and suspension WC-Co feedstock

Corrosion properties of nanostructured coatings deposited by Suspension High Velocity Oxy-Fuel (S-HVOF) via an aqueous suspension of milled WC-Co powder were compared with conventional HVOF sprayed coatings. Microstructural evaluations of these coatings included X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDX). The corrosion performance of AISI440C stainless steel substrate and the coatings was evaluated in a 3.5 % wt. NaCl aqueous solution at ~25oC. The electrochemical properties of the samples were assessed experimentally, employing potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The potentiodynamic polarization results indicated that coatings produced by S-HVOF technique show lower corrosion resistance compared to the coatings produced by HVOF-JK (HVOF Jet-Kote) and HVOF-JP (HVOF JP5000) techniques. Results are discussed in terms of corrosion mechanism, Bode and Nyqvist plots, as well as equivalent circuit models of the coating-substrate system.