In powder bed fusion-electron beam melting, the alloy powder can scatter under electron beam irradiation. When this phenomenon-known as smoking-occurs, it makes the PBF-EBM process almost impossible. Therefore, avoiding smoking in EBM is an important research issue. In this study, we aimed to clarify the effects of powder bed preheating and mechanical stimulation on the suppression of smoking in the powder bed fusion-electron beam melting process. Direct current electrical resistivity and alternating current impedance spectroscopy measurements were conducted on Inconel 718 alloy powder at room temperature and elevated temperatures before and after mechanical stimulation (ball milling for 10-60 min) to investigate changes in the electrical properties of the surface oxide film, alongside X-ray photoelectron spectroscopy to identify the surface chemical composition. Smoking tests confirmed that preheating and ball milling both suppressed smoking. Furthermore, smoking did not occur after ball milling, even when the powder bed was not preheated. This is because the oxide film undergoes a dielectric-metallic transition due to the lattice strain introduced by ball milling. Our results are expected to benefit the development of the powder bed fusion-electron beam melting processes from the perspective of materials technology and optimization of the process conditions and powder properties to suppress smoking.
Keywords: Inconel 718; Mott insulator; additive manufacturing; ball milling; electrical resistivity; electron beam melting; metal–insulator transition; oxide film; powder bed fusion; smoking.