Evaluation of the electrochemical behavior of HVOF-sprayed alloy coatings

High-velocity oxy-fuel (HVOF) spraying is a versatile technique that can yield high-density coatings with porosities less than 1% by optimization of the process variables. Oxidation of the coating material can be greatly reduced by inert gas shrouding during the spraying process. This work evaluates the electrochemical behavior of HVOF-sprayed coatings aimed to have better or similar corrosion behavior as stainless steel AISI 316 in acidic medium. A total of eight different chromium-containing coatings with varying proportions of alloying elements such as Ni, Mo, Si, Fe, Co, W, B and C have been studied in hydrochloric acid medium. Porosity measurements, gravimetric analysis, open-circuit potential measurements, potentiodynamic polarization and optical microscopy have been performed. The electrochemical behavior of each coating has been compared with that of bulk AISI 316. The results indicate that HVOF-sprayed AISI 316 coating offers a lower corrosion resistance compared to bulk AISI 316. High nickel- and chromium-containing coatings appear to offer a corrosion resistance comparable to bulk AISI 316. However, results indicate that other alloying elements like molybdenum might be essential for obtaining higher corrosion protection.