Microstructural Characterization and Modeling of Beam Speed Effects on Ti-6Al-4V by Electron Beam Additive Manufacturing
In this study, the influence of the beam scanning speed to the microstructure of Ti-6Al4V parts processed by EBAM is investigated. EBAM parts were fabricated with 4 different scanning speeds, ranging from 214 mm/s to 689 mm/s, and the microstructures were studied. In addition, the volume fractions of different phases were obtained by thermal and phase transformation modeling. The microstructure is characterized by columnar structures of prior β grains along the build direction, and fine Widmanstätten (α+β) structure and α′ martensites are presented inside of the prior β. Both the prior β grain size and α-lath thickness decrease with the increase of the scanning speed. For the phase constitution, the volume fraction of α′ increases with the scanning speed while the volume fraction of α decreases due to the increase of cooling rate during solid phase transformation. The results from the analytical phase transformation model are consistent with the microstructure characterization from the experiment.