Effects of the higher accelerating voltage on electron beam powder-bed based additive manufacturing of Ti6Al4V alloy

Abstract

Electron beam powder bed fusion (EB-PBF) uses electron beams as the heat source to melt the powder layer by layer and produces parts with complex shapes. The power of the electron beam, which is determined by its accelerating voltage and beam current, is one of the key process parameters. Coupled with other process parameters, the electron beam power substantially affects the quality and mechanical properties of the final parts. Most studies on EB-PBF have been based on a constant accelerating voltage to consider the electron beam current, beam energy density, or scanning strategy. However, the influence of the accelerating voltage on the performance of the electron beam and the mechanical properties of the EB-PBF parts have rarely been studied. To this end, in this study, two accelerating voltages of 60 and 90 kV were used for the single-track scans and fabrication of cubic samples of Ti6Al4V alloy via EB-PBF. The surface morphologies, densities, microstructure and mechanical properties of the as-built EB-PBF samples were investigated. The results reveal that the interaction between the electron beam and metal vapor causes a considerable dissipation of electron beam energy. Increasing the accelerating voltage from 60 to 90 kV not only reduces the beam diameter from 401 to 308 µm and increases the depth of the beam penetration and molten pool, but also reduces the dissipation effect of the metal vapor, thereby increasing the proportion of the beam energy absorbed by the material, and decreasing the energy density necessary for fabricating dense parts. Furthermore, the experimental results indicate that raising the accelerating voltage of the electron beam can improve the energy efficiency, and bring more advantages to the EB-PBF process. For instance, a smaller beam current and shorter preheating time, which would reduce the “smoking” risk and increase the building rate.