Additive manufacturing by laser powder bed fusion (LPBF) of high entropy alloys produces dense samples by successive sintering of layers of pre-alloyed particles. Alternatively, one can also start with a power blend and initiate in-situ alloying by the laser beam, a flexible approach, which significantly accelerates processing.
In this contribution, we employ the molecular dynamics simulations using a modified embedded atom method interatomic potential parametrized by Choi et al. to consider different stages of LPBF. During LPBF, the powder is fully melted and solidified on a substrate that acts as a large heat sink. We investigate the influence of the initial pulse on high entropy alloy (HEA) LPBF and the heat flow from the substrate.
We find that the diffusion in prealloyed HEA melt significantly differs from in-situ alloyed melt, and the arrangement of atoms during in-situ alloying also influences intermixing. Our simulations reveal that in-situ alloying of HEA is possible, if the particles are in melt for a sufficiently long time, compared to prealloyed particles (which can be achieved, for example, with lower laser speed).
We explore the influence of various process parameters such as temperature field, melt pool size, laser spot size, substrate type, etc. on microstructural features in HEA in-situ alloying by LPBF. We investigate the impact of the substrates (Mn, HEA, Ni, Cr) with different melting temperature on HEA LPBF, which can significantly influence on the molten zone and solidification to crystalline or glassy states. The results show that the modelled structures delicately depend on the interplay of laser parameters, heat transport, interdiffusion, substrate and geometric factors.