High-entropy alloy formation by laser beam powder bed fusion of prealloyed nanoparticles and powder blends: Insights from molecular dynamics simulations

Laser Beam Powder Bed Fusion (PBF-LB) facilitates in situ alloying of powders and powder blends even at the nanoscale level, thus allowing for the simultaneous phase formation and shaping of intricate geometries. For unraveling the details of mass and heat transport processes in nanopowders under far-from-equilbrium conditions, molecular dynamics simulations are a helpful tool. In this study, we compare pre-alloyed equimolar FeCrCoMnNi and FeCrCoAlNi high-entropy alloy (HEA) nanoparticles with nanopowder blends composed of elemental nanoparticles deposited on support layers of varying melting temperatures (Mn/Al, HEA, and Ni) after the impact of a single laser pulse. From a powder bed of pre-alloyed nanoparticles, we obtain dense layers with some surface segregation and observe a high density of dislocations, stacking faults and vacancy clusters. The number of lattice defects is reduced, however, if a support layer with high melting point is used. When using a nanopowder blend, a dense but chemically inhomogeneous layer forms. This is due to the limited lifetime of the liquid phase. Simulations of stacked nanolayers of 2 nm width reveal that a critial lifetime of the liquid phase larger than 2 ns is necessary for obtaining full mixing. • The lifetime of the liquid phase is too short for full intermixing. • Mn and Al segregate due to lower surface energy and higher diffusivity. • The substrate influences on resolidification and formation of lattice defects. • There is a higher density of stacking faults in the powder layer on Ni substrate. • There are vacancies and vacancy clusters for all the considered substrates. • In-situ alloying of nanopowder blends requires several scans.