Microstructure evolution in laser-based powder bed fusion of metals

Laser-based powder bed fusion (LPBF) of metals offers the unique possibility of creating the microstructure voxel-by-voxel. The minimum voxel size in each direction is dependent on material dosing accuracy coupled with laser processing parameters. The rapid solidification conditions during LPBF lead to material heterogeneity coupled with hierarchical and non-equilibrium microstructures. The current paper delves into two different pathways available currently to control microstructure in LPBF, namely: in-situ microstructure control through material distribution to form functionally graded components with complex interfaces; application of post-processing thermo-mechanical treatments to control the microstructure. Unlike traditional manufacturing methods, each voxel in LPBF can be further processed multiple times after the first fusion process. Such in-situ processing presents further opportunity for tailoring the microstructure of each voxel in 3D. A future perspective is thus offered on the opportunities to control and engineer LPBF microstructures in metals.