In-situ characterization of defect formation and elimination dynamics during electron beam melting using high-speed X-ray imaging

• Directly observed defect formation and elimination dynamics in electron beam melting. • Revealed pore formation mechanisms from feedstock powders, pre-existing defects, and solidification front capturing in EBM. • Revealed pore elimination mechanism due to metal vapor condensation during EBM. • Unraveled crack elimination mechanism through remelting under vacuum condition. Electron beam melting (EBM), also known as electron beam powder bed fusion (EB-PBF), is a metal additive manufacturing (AM) technology that can make metal parts that are difficult, inefficient, or unachievable through conventional manufacturing routes and other AM technologies. However, a comprehensive understanding of the dynamics of electron beam-matter interactions in EBM remains elusive, which is a barrier for the development and adoption of EBM technology. Here, we report the dynamics and mechanisms of pore formation, pore elimination, and crack elimination in EBM. Three mechanisms of pore formation are observed: (1) pore formation from feedstock powders, (2) pore formation from pre-existing defects, and (3) pore captured by solidification front. One pore elimination mechanism is discovered: pore elimination due to metal vapor condensation, which is unique to EBM. One crack elimination mechanism is uncovered: crack elimination through remelting. These results will enhance the understanding of defect formation and evolution mechanisms in EBM and may inspire the invention of effective approaches to mitigate and control defects (porosity and cracks) in EBM.