Corrosion and thermal processing in cold gas dynamic spray deposited austenitic stainless steel coatings

Abstract

This thesis presents research on the corrosion properties and effects of heat treatment on austenitic stainless steel coatings produced by the cold gas dynamic spray process on 316L stainless steel substrates. Previous work on the use of the low-pressure cold spray process to spray austenitic stainless steel was reproduced and validated. Heat treatment of the coatings was found to reduce porosity and evidence was found of recrystallization of the coatings. No significant changes in elemental distribution were found to occur during heat treatment. Corrosion testing was conducted by salt fog testing and anodic polarization. Coatings in the as-sprayed condition were found to be less corrosion resistant than bulk 316L stainless steel. Heat treated samples were observed to show corrosion resistance even worse than as-sprayed coatings. In fact, all heat treated samples exhibited little or no passivation behavior. Grain boundary sensitization is suspected to a probable cause for poor corrosion resistance in some samples and the presence of ferrite in the powder and coatings may also be a cause of corrosion resistance that is worse than the fully austenitic substrate.