[en] A number of laser and electron beam-based fabrication processes are under consideration for aerospace components, where the ability to obtain a consistent and desirable microstructure and resulting mechanical properties is of critical concern. To this end, this work employs a combination of analytical and numerical modeling approaches to investigate the effects of process variables and size-scale on solidification microstructure (grain size and morphology) in beam-based fabrication of bulky 3D structures. Thermal process maps are developed for predicting solidification microstructure in any material system, and results are plotted on solidification maps to investigate trends in grain size and morphology in Ti-6Al-4V. The results of this work suggest that changes in process variables (beam power and velocity) can result in a grading of the microstructure throughout the depth of the deposit, with a transition from columnar to mixed or equiaxed microstructure at higher powers.