Smoke Suppression in Electron Beam Melting of Inconel 718 Alloy Powder Based on Insulator-Metal Transition of Surface Oxide Film by Mechanical Stimulation.

Akihiko Chiba,Kenta Aoyagi,Yohei Daino,Kenta Yamanaka

doi:10.3390/ma14164662

Abstract

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.

Highlights

Electron beam melting (EBM) is an additive manufacturing process that produces components by selectively melting layers of metal powder based on three-dimensional computer-aided design data [1,2,3,4,5]
Materials surface is covered with an insulating Cr2 O3 passivation film with a thickness of several nanometers [11], and investigated the temperature dependence of the electrical properties, The powder used in this study was Inconel 718 powder fabricated via plasma at such as the electrical resistivity and alternating current (AC) impedance, and the thermal stability of the surface ization, which was purchased from Arcam AB
Smoking, which is a problem in electron beam additive manufacturing, is generated by the Coulomb repulsive force acting between the powder particles, because they become negatively charged under electron beam irradiation

Summary

Introduction

Electron beam melting (EBM) is an additive manufacturing process that produces components by selectively melting layers of metal powder based on three-dimensional computer-aided design data [1,2,3,4,5]. Compared to laser beam additive manufacturing processes, EBM has many advantages [2] with regard to the processing speed, energy density, residual stresses, and applicability to metal powders with high melting temperatures such as Ta [6]. The electron beam has a negative charge, which introduces several complexities with regard to the control of the EBM process. This problem must be overcome to expand the application scope of PBF-EBM processes

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Conclusion