Crystal Plasticity Modeling of Dislocation Density Evolution in Cellular Dislocation Structures

The complex thermal cycles during the solidification process in metal additive manufacturing (AM) lead to the formation of high-density dislocation networks, organizing into submicron-scale cellular structures. These ultrafine structures are recognized as crucial for enhancing the mechanical properties of AM metals. In this study, we investigate the evolution of dislocation density within these cellular structures under plastic deformation and its impact on mechanical response using dislocation density-based crystal plasticity finite element (CPFE) modeling. The model incorporates the evolution of both statistically stored dislocation (SSD) and geometrically necessary dislocation (GND). Our simulations reveal that the yield and flow stresses of dislocation cell structures exceed predictions based on the rule of mixtures (ROM). Additionally, the SSD density increases at a higher rate than the GND density. Factors such as the volume fraction of the cell wall, cell diameter, and initial dislocation density difference between the cell wall and interior significantly influence GND accumulation across different regions of the cellular dislocation structures.