Recrystallization as a tool to characterize and control the properties of cold sprayed materials: case study on 316L steel
Owing to the unique buildup mechanisms, recrystallization in cold sprayed materials significantly differs from that in conventional counterparts. In this study, the relationship between deformation-induced microstructural heterogeneity, recrystallization behavior, and mechanical properties of cold sprayed materials was investigated using EBSD and nanoindentation. The 316L stainless steel was selected as a model material. The deposit was characterized in its as-sprayed condition and after annealing at temperatures between 900 and 1100 K. Thermomechanical estimates suggest that locally, temperature can rise over 1000 K and very high dislocation densities (up to 1017 m-2) form at particle boundaries during impact, providing a strong driving force for subsequent recrystallization. The EBSD observations confirmed the intense defect accumulation and grain fragmentation localized near the particle interfaces. Recrystallization initiated preferentially in these highly strained areas after annealing at 1000 K and progressed with increasing temperature and holding time, leading to complete recrystallization after 1 h at 1100 K. The recrystallized grain-size distribution was well described by a heavy-tailed log-normal distribution, which indicates extremely heterogeneous strain partitioning generated during particle impacts. Nanoindentation measurements showed that the high hardness of the cold sprayed deposit remained largely unchanged after annealing at 900 K but gradually decreased as recrystallization progressed. We further demonstrate that controlled post-spray recrystallization can serve as a powerful tool for characterizing deformation during deposition and for tailoring the microstructure and mechanical properties of cold-sprayed materials.