Heat Treatment of Recycled Battlefield Stainless-Steel Scrap for Cold Spray Applications

This work explores the impact of thermally preprocessing recycled austenitic stainless-steel powder for solid-state cold spray metal additive manufacturing with a focus on increasing deposition quality and coating density while maintaining mechanical integrity. The recycled stainless-steel scrap was gas-atomized using a novel mobile foundry manufactured by MolyWorks Materials Corporation. The powder was thermally treated based upon thermodynamic modeling using Thermo-Calc. The powder and sprayed specimens were characterized using particle size-shape analysis, microscopy, x-ray diffraction, and nanoindentation. Diffraction results highlighted the presence of both austenite and ferrite phases in the powder. Nanoindentation confirmed that thermally processing the feedstock powder at the austenitization temperature decreased the amount of ferrite present, which was consistent with the porosity observed in the deposits due to the lower yield strength of austenite relative to ferrite. The untreated powder deposits exhibited extensive porosity and microcracking, as opposed to the virtually fully dense deposit from the heat-treated powder.