Corrosion Resistance of Post Heat Treated HVOF Coatings Based on Cermet-Ni Based Alloys Mixture

The aim of the present work was to study the effect of the mixing NiCrBSi with different amounts of WC-12%Co commercial powders on the corrosion resistance of deposited coatings using high velocity oxy-fuel (HVOF) process. For such purpose, NiCrBSiWFe powder alloy was mixed mechanically with different amounts of WC-12%Co powder. The powder mixture was thermal sprayed using a JP-5000 gun on an AISI 1020 steel substrate. An oxyacetylene flame was used to perform the post heat treatment, which was applied during 300 seconds. The coating’s corrosion resistance was evaluated by conducting potentiodynamic polarization curves, in a aerated 3,5 % sodium chloride solution. Scanning electron microscopy (SEM), X-Ray Diffraction (XRD) and Auger electron spectroscopy techniques were employed for the coatings microstructural characterization before and after the corrosion test in order to identify the possible mechanisms of corrosion. The investigations showed that mixing WC-Co with NiCrBSiWFe powder no affected significantly the corrosion coating performance. On the other hand, it was shown that the post coating heat treatment has substantially improved the corrosion resistance of it. This improvement was related to the considerable decrease of the porosity as consequence of the sealing effect due to the oxyacetylene flame on the coating surface.