Optimisation of stainless steel cold spray coatings using mixed particle size distributions

Porosity in type 316 L stainless steel cold spray coatings is studied from two different aspects. The first is to examine, for a given level of porosity, the effect of coating thickness on corrosion behaviour. Beyond a critical coating thickness the substrate is no longer attacked in polarisation tests, which has implications for coatings that contain some porosity (including some thermal spray coatings). The second aspect examined is to approximate the stainless steel particles as non-deforming, and apply the powder metallurgy practice of mixing particle size distributions to improve coating density. The results show that coatings sprayed using mixed particle size distributions can have similar properties to those sprayed using fine particles alone, but without the processing difficulties of fine particles such as inconsistent powder feeding or nozzle fouling.

Research highlights
► We address the issue of porosity in austenitic stainless steel coatings.
► These particles undergo little deformation on impact.
► With a small level of porosity, coatings beyond a critical thickness are protective.
► Mixing particle size distributions reduces coating porosity.
► This is a more practical approach than spraying with fine particles.