Cold Spray of Bimodal Size 316L/Fe Powder Mixtures: Coating Microstructure and Cold Sprayability

In this study, a 43 μm 316L stainless steel and a 23 μm commercial purity Fe powder was used as feedstocks. The following coatings were made by cold spray: single component 316L, Fe, and 316L/Fe composites with feedstock mixing compositions of 20 wt.% Fe (20Fe), 50 wt.% Fe (50Fe) and 80 wt.% Fe (80Fe). The as-sprayed coatings were analysed through coating microstructure (inter-lamellar crack, flattening ratio, composition) and cold sprayability (DE, porosity, bond strength). The number fraction of the 316L/Fe particles in a mixture was calculated based on its respective weight fraction and was used to evaluate the degree of mixing. Using this metric, the effect of the feedstock mixing composition on the cold sprayability of bimodal size 316L/Fe powder mixtures was discussed. Results show that the multi-particle arrangement of the bimodal size 316L/Fe mixtures upon impact could affect the mixture cold sprayability. In particular, the mixture with a 316L/Fe number fraction of 1:8 (50Fe) can exhibit the lowest porosity as the feedstock obtains a dense packing and sufficient particle interaction during impact; the mixture with a 316L/Fe number fraction of 1:32 (80Fe) can exhibit the highest DE due to the combined effects of tamping and retention.