Neutron diffraction-assisted constitutive modeling of directed energy deposited CoCrFeMnNi high entropy alloy

The cellular structure is a crucial factor in understanding the mechanical properties of metal additive manufacturing (MAM) processed components. Its systematic monitoring and evaluation are essential for developing new alloys optimized for MAM. This study presents in situ neutron diffraction experiments and dislocation density-based constitutive modeling for the CoCrFeMnNi high entropy alloy (HEA) produced via directed energy deposition (DED). A dislocation density-based constitutive equation, grounded in the Kocks-Mecking-Estrin model, was employed to represent the HEA's cellular structure, combining in situ neutron diffraction data for enhanced accuracy. By parametrically analyzing the constitutive model, we found that the rates of dislocation accumulation and annihilation in the as-built sample were lower than in the heat-treated sample, which lacks a cellular structure. These observed differences can be attributed to the action of a dislocation forest network and local variations in stacking fault energy due to elemental segregation. Furthermore, the study examined dislocation density changes across different regions (cell interiors and cell walls) and compared these observations with dislocation cells formed during plastic deformation.