Operando electron optical monitoring for real-time evaporation detection in electron beam powder bed fusion

Abstract Operando electron optical (ELO) monitoring offers a promising approach for real-time process control in electron beam powder bed fusion (PBF-EB). While in-situ ELO imaging of the solidified surface—as an extra process step—is well established, the electron signal during melting remains insufficiently investigated. In this study, a self-developed four-detector ELO system with a negative bias voltage is used to analyze the operando signal during melting of a Ti–6Al–4V plate and its correlation with evaporation. Square melt areas were produced using different beam current and scan velocity combinations at a constant area energy. A time delayed signal component is attributed to positively charged metal ions formed by evaporation-induced vapor ionization. The extracted ion signal shows strong qualitative agreement with the simulated evaporation, both for the average evaporation intensity in the quasi-stationary regime and for the settling phase within the first hatch lines. In addition, it resolves local evaporation changes during hatching, including maxima at turning points caused by heat accumulation, followed by a systematic decrease in evaporation intensity. These results provide the first experimental evidence that operando ELO could be a strong candidate for real-time monitoring of evaporation in PBF-EB and a promising tool for assessing and controlling the thermal homogeneity of the melting process.