Vapor chemical composition in electron beam powder bed fusion using Ti–6Al–4V powder

This study investigates the vapor chemical composition, during the melting step of an electron beam powder bed fusion process using Ti–6Al–4V powder. A phenomenological model is proposed to analyze and discuss the vapor composition. The model focus on the heat dissipation of the molten powder. Vapor stream from the molten powder is compounded by vapor saturation pressure and rapid boiling (ebullition) of the molten pool. The model is based on post mortem results of condensed vapor (thin film), which were analyzed by X-ray photoelectron spectroscopy and glow discharge optical emission spectrometry, providing quantitative and in-depth profile data. It was found that the ratio of [Al] to [Ti] in the vapor stream is influenced by the melting conditions. As the e-beam current increases, the heat dissipation reaches the ebullition domains, and the [Al]/[Ti] ratio tends to the molar ratio of the precursor powder (Ti–6Al–4V), indicating the complete overheating of all the alloy elements.