Connecting processing conditions to microstructure evolution in laser powder bed fusion via defect modeling

The highly localized multiphysics nature of laser powder bed fusion (PBF-LB) induces complex transient temperature and strain profiles that challenge predictive modeling of microstructure evolution and resulting mechanical properties. Discrete dislocation dynamics (DDD) simulations were conducted to model the evolution of dislocation structures during rapid cooldown after laser powder bed fusion (PBF-LB) of 316L stainless steel. The DDD model incorporated the transient temperature profiles and stress evolution from finite element (FEM) thermomechanical simulations. Three cooling rate profiles were modeled. At lower cooling rates, higher overall dislocation densities and earlier emergence of organized dislocation cell structures oriented along [100] directions were observed. The accumulation of dislocations at solute-enriched cell walls increased progressively during cooling, independently of the cooling rate. Capturing this transient dislocation evolution provides insights into defect formation mechanisms and enables direct comparisons to experimental characterization. This will support microstructure-informed process optimization for tailored mechanical performance of additively manufactured alloys.