Exploring Microstructure Evolution in CoCrFeNi High-Entropy Alloy During Laser Powder Bed Fusion: A Molecular Dynamics Simulation

Simulations can make an important contribution to clarifying phenomena related to processing metals via additive manufacturing such as the widely used laser powder bed fusion (LPBF) technology. This study presents a large-scale molecular dynamics (MD) simulation model to investigate the microstructural evolution of the CoCrFeNi high-entropy alloy during the LPBF process which is a widely used metal additive manufacturing method. The model includes a densely packed powder bed and a substrate and employs a continuous laser track to simulate localized heating as well as solidification by temporally controlling the temperature distribution within the resulting molten pool. Incomplete melting and evaporation are identified by the present MD simulation as two key mechanisms resulting in the formation of defects which are additionally confirmed by experiments. We demonstrate that the resulting laser energy density significantly impacts the migration of grain boundaries thus affecting the grain size. Higher energy densities promote the coalescence of grains and epitaxial growth by facilitating the fusion of grains. Perfect dislocations are primarily found at grain boundaries due to misaligned orientations, while partial dislocations occur within grains as rapid melting and solidification prevent atoms from reaching their equilibrium positions. Our MD simulation provides deep insights into atomic flow behavior within the molten pool, which is dominated by the Marangoni effect, during LPBF processing of the CoCrFeNi HEA. Different atoms demonstrate a consistent clockwise flow which ultimately leads to a uniform distribution of elements, ensuring homogeneity in the final alloy.