Non-Equilibrium Solidification Behavior With Solute Trapping 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 mechanical properties and hot cracking resistance. Notably, the powder characteristics influence heat absorption and conduction, thereby altering the molten pool behavior and solidification parameters. However, the effect of powder feedstock on non-equilibrium solidification during PBF has not been widely investigated. In this study, a CoCrMo alloy was built using powders prepared by gas-atomization (GA) and plasma rotating electrode process (PREP). Under the given operating conditions, the samples built with the two powders were experimentally characterized and their compression properties were compared. By performing multi-scale numerical simulations, powder 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 upon appropriated size control, compared to 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 is facilitated, thereby suppressing microsegregation. The findings contribute to PBF knowledge related to feedstock, thus proving to be an essential reference for selecting and optimizing metallic powders applicable to additive manufacturing.