Non-equilibrium solidification behavior associated with powder characteristics during electron beam additive manufacturing

Abstract

For components built by powder bed fusion with electron beam (PBF-EB), the resulting microstructure arising from non-equilibrium solidification, microsegregation and the formation of interdendritic phases significantly affects the material properties. Notably, the powder characteristics influence the heat absorption and conduction, thereby altering the molten pool behavior and solidification parameters. However, the effect of the powder feedstock on solidification during PBF has not been widely investigated. In this study, a CoCrMo alloy was fabricated using powders prepared by gas-atomization (GA) and plasma rotating electrode process (PREP). Under the given operating conditions, samples built using the two powders were characterized and compared. By performing multi-scale numerical simulations, melting and solidification were visualized and analyzed to elucidate the mechanism through which the powder characteristics influence the non-equilibrium solidification behavior during PBF-EB. The study revealed that after appropriate size control, compared with the GA powder, the PREP powder had a smaller specific surface area and higher sphericity; thus, the generated powder layer exhibited higher heat absorption and dissipation rates. Therefore, a high solidification rate was facilitated, thereby suppressing microsegregation. These findings contribute to PBF knowledge related to feedstock, proving to be an essential reference for selecting and optimizing metallic powders applicable to additive manufacturing.