Three-dimensional spot melting patterns in electron beam powder bed fusion: high efficiency and tailored texture

Spot melting is quickly gaining ground on line-based scanning strategies typically used in electron beam powder bed fusion, offering a greater degree of freedom, suitability for complex geometries and the ability to control the local microstructure. Spot melting where the electron beam jumps from one location to another should be considered from two separate perspectives: the underlying geometric information, namely the lattice structure on which the spots are arranged, and the spot sequence that governs the order in which locations are visited by the electron beam. In recent years, a growing number of spot melting strategies have emerged, aiming to change the grain morphology by locally forcing a columnar to equiaxed transition using energies that are significantly higher compared to those traditionally used with line-based scanning. This contribution focuses on the geometrical aspect of the spot melting strategies, namely the three-dimensional spot arrangement and its potential use as a tool for texture design. We demonstrate that a well-defined stacking of two-dimensional hexagonal lattices to create three-dimensional lattice structures, significantly alters the minimum energy density for fabricating the Ni-base superalloy IN718. More importantly, we show that it is possible to directly translate the symmetry of the three-dimensional lattice into texture symmetry.