Microstructure and corrosion resistance of HVOF sprayed 316L stainless steel and Hastelloy C coatings

Abstract

In order to develop dense corrosion resistant coatings by thermal spraying, 316L stainless steel and Hastelloy C alloy powders were sprayed by an HVOF thermal spraying apparatus onto a mild steel substrate. The microstructure, pore size distribution, composition and corrosion resistance of the obtained coatings were evaluated experimentally. Corrosion resistance in seawater was examined by monitoring the impedance and corrosion potential of samples immersed in artificial seawater at 300 K over a period of more than 3 months and also by polarization measurement. It was found that the stainless steel coatings composed mainly of plastically deformed particles and some splats that were molten at the impact. By increasing the combustion pressure, the porosity measured by a mercury porosimeter was reduced to below 1%. In comparison, Hastelloy C deposits sprayed under a standard condition were so dense that their porosity could not be measured by the porosimeter. The polarization curves and the results of impedance monitoring exemplified that the Hastelloy C coatings possess much superior corrosion resistance to the stainless steel coatings in seawater, which was attributed mainly to the higher density and better adhesion of the Ni-base alloy coatings.