The development of a sample environment for in situ x-ray characterization during metal Electron Beam Powder Bed Fusion (PBF-EB), called MiniMelt, is presented. The design considerations, the features of the equipment, and its implementation at the synchrotron facility PETRA III at Deutsches Elektronen-Synchrotron, Hamburg, Germany, are described. The equipment is based on the commercially available Freemelt ONE PBF-EB system but has been customized with a unique process chamber to enable real-time synchrotron measurements during the additive manufacturing process. Furthermore, a new unconfined powder bed design to replicate the conditions of the full-scale PBF-EB process is introduced. The first radiography (15 kHz) and diffraction (1 kHz) measurements of PBF-EB with a hot-work tool steel and a Ni-base superalloy, as well as bulk metal melting with the CMSX-4 alloy, using the sample environment are presented. MiniMelt enables time-resolved investigations of the dynamic phenomena taking place during multi-layer PBF-EB, facilitating process understanding and development of advanced process strategies and materials for PBF-EB.

Electron beam–powder bed fusion (PBF-EB) is an additive manufacturing process that utilizes an electron beam as the heat source to enable material fusion. However, the use of a charge-carrying heat source can sometimes result in sudden powder explosions, usually referred to as “Smoke”, which can lead to process instability or termination. This experimental study investigated the initiation and propagation of Smoke using in situ high-speed synchrotron radiography. The results reveal two key mechanisms for Smoke evolution. In the first step, the beam–powder bed interaction creates electrically isolated particles in the atmosphere. Subsequently, these isolated particles get charged either by direct irradiation by the beam or indirectly by back-scattered electrons. These particles are accelerated by electric repulsion, and new particles in the atmosphere are produced when they impinge on the powder bed. This is the onset of the avalanche process known as Smoke. Based on this understanding, the dependence of Smoke on process parameters such as beam returning time, beam diameter, etc., can be rationalized.

Electron beam powder bed fusion (PBF-EB) is an additive manufacturing technique that fabricates customized components using an electron beam in a controlled vacuum environment. Maintaining high vacuum quality is crucial to prevent feedstock contamination. However, the inherent nature of the PBF-EB process introduces a gas load into the system, potentially affecting process stability and product quality. This study utilizes a residual gas analyzer to investigate experimentally outgassing associated with various process activities, including electron beam radiation, rake movement, and powder outgassing. The findings indicate that hydrogen, water, nitrogen, oxygen, argon, and carbon dioxide are the predominant gases present during PBF-EB processes. Moreover, rapid outgassing is identified as a likely trigger for powder movement, marking the initial stage of the smoke phenomenon. These results contribute fundamental insights into the gas atmospheres in PBF-EB processes.

Electron optical imaging shows significant potential as a process monitoring technique in electron beam powder bed fusion. When the primary electron beam interacts with substrate materials, electrons are emitted from the surface. These electrons carry essential surface information that can be used for monitoring. Usually, an additional step is incorporated into the process where the electron beam scans the entire surface, generating optical images layer by layer, known as in situ electron optical imaging. However, the potential of electrons emitted during the melting process, called operando signals, has not been fully utilised. By correlating X-ray computed tomography measurements, in situ, and operando electron optical monitoring, this study reveals a strong correlation between outliers in the operando signal and the start of defect formation. The defect initiation is often associated with strong balling which results in abnormal high operando signal intensity. The defect development leads to topographical features that can be effectively captured by subtracting operando signals from opposite detector pairs. These observations suggest that operando electron optical imaging is a strong tool to identify the initiation of faults in electron beam powder bed fusion.