Cold spray-friction stir hybrid additive manufacturing of 316L SS: Feasibility, microstructure, and mechanical performance

Cold spray additive manufacturing of strain hardenable austenitic steels often yields poor properties in the as-fabricated state. The cold spray-friction stir additive manufacturing (CFAM) process, which combines cold spray (CS) deposition with friction stir processing (FSP), has been shown to enhance the properties of ductile materials, particularly aluminum alloys. However, its potential for austenitic steels remains largely unexplored. In this study, the feasibility of additively manufacturing bulk 316L stainless steel using hybrid CFAM process is demonstrated by overcoming the inherent difficulties in FSP of brittle CS deposits through a specific processing strategy. The study further examines the relationship between processing, microstructure, and mechanical properties of CFAM fabricated 316L compared to CS produced 316L, highlighting the governing recrystallization and strengthening mechanisms. The results show that CFAM produced 316L exhibits a fully recrystallized microstructure characterized by equiaxed grains and minimal porosity. In contrast, CS fabricated 316L shows a partially recrystallized microstructure with high porosity and numerous elongated grains. Additionally, CFAM fabricated 316L demonstrates superior tensile properties and ductile fracture behavior, while CS fabricated 316L displays brittle fracture characteristics. This study suggests that CFAM is a promising method for producing strain-hardenable steel components, with significant potential to optimize properties for diverse applications.