Multi-Scale Structural Effects of External Electrical Fields of Melt Tracks in Laser Powder Bed Fusion

The dynamics of the melt pool critically influence the structure and resultant properties of resolidified metals in laser-based powder bed fusion and related 3D printed applications. While the influence of external electric fields on the surface and bulk properties of fluids at ambient conditions is well documented, their impact on the transient, high-temperature melt pools characteristic of powder bed fusion remains largely unexplored, and their broader applicability is unclear across multiple length scales. Here, we reveal how external non-contact EFs influence both macro- and microstructures during laser scanning. EFs have the ability to influence structure through a fundamentally different mechanism than thermal approaches. Qualitative and quantitative analyses show that EFs drastically improve continuity and stability of metal tracks while enhancing surface smoothness in micro- and nano-scale. Beyond the surface, EFs drive the formation of equiaxed grains, promoting grain refinement in bulk. Structural effects depend on EF type as well as the orientation and direction with respect to the laser scanning direction. Moreover, we demonstrate that EFs can be effectively coupled with advanced beam-shaping strategies, yielding synergistic structural control and indicating their potential as a versatile and adaptable tool for next-generation advanced manufacturing systems.