Recrystallization-based grain boundary engineering of 316L stainless steel produced via selective laser melting

Grain boundary engineering (GBE) is a thermomechanical processing strategy to enhance the physical and mechanical properties of polycrystalline metals by purposely incorporating special types of grain boundaries—such as twin boundaries (TB)—in the microstructure. Because of the multiple strain-annealing cycles involved, conventional GBE is not directly applicable to near-net-shape parts, such as those produced via additive manufacturing (AM) technology. In this study, we explore a different GBE processing route that leverages TB multiplication during recrystallization of austenitic 316L stainless steel produced via selective laser melting (SLM). We find that recrystallization requires a minimum level of mechanical deformation, which scales with the laser scanning speed employed during SLM. We ascribe this relationship to the cell size and the amount of solute segregating at cell boundaries during rapid solidification, which are inversely and directly proportional to the laser scanning speed, respectively. The coarser the cell structure and the more uniform the chemical composition, the easier the nucleation and growth of recrystallized grains. Our results provide the groundwork for devising AM-compatible GBE strategies to produce high-performance parts with complex geometry.