Electron beam powder bed fusion (PBF-EB) of Ni-base superalloys such as CMSX-4 is a demanding process. Using conventional PBF-EB machines, process observation is done by mounting optical camera systems on viewing windows at the top of the build chamber. However, the concomitant metallization blocks optical observation methods with increasing build time. Therefore, build quality evaluation is normally done after the process utilizing visual inspection or subsequent metallurgical analysis. In this work, CMSX-4 is processed using a freely programmable PBF-EB machine with an electron optical (ELO) imaging system. It consists of a four-segment ELO detector and in-house developed imaging software. The ELO system works reliably for almost 30 h of build time and allows a layerwise monitoring of the build area. A comparison of in-situ ELO monitoring and the sample surfaces shows remarkable accordance. Furthermore, ELO imaging is applied to exemplarily document surface cracking over long build times. Therefore, the present study successfully demonstrates the application of ELO imaging for improved process control under the demanding test conditions of Ni-base superalloys.

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.

The exceptional properties of tungsten make it a very attractive material for advanced applications, however, it is challenging to process. Research on electron beam powder bed fusion (PBF-EB) of tungsten is limited but promising. Previous work has mostly focused on low beam powers and scan velocities, which limits the efficiency of the manufacturing process. A higher processing speed is required for economical production of large tungsten components. This paper studies PBF-EB processing of pure tungsten with a power of 5 kW using a Freemelt ONE and scan velocities of several meters per second, making use of the full capabilities of PBF-EB technology. The required energy input for preheating of the powder bed to achieve dense and crack-free bulk samples is investigated in detail. Then, to optimize the heating energy input, a localized heating strategy is introduced where only the sample cross section is heated after general preheating. Hereby, the required energy input for achieving crack-free tungsten was decreased by 50%. Furthermore, the layer time was reduced from initially 44 s to 30 s, since only a short cooling step was required to avoid overheating of the machine. Finally, dense and crack-free tungsten blocks with 80 mm height were successfully fabricated, thus verifying the applicability of high-power PBF-EB for efficiently creating solid tungsten parts. Microstructural and hardness analysis along the build height revealed a columnar grain structure with a slight grain coarsening and corresponding decrease in hardness towards the top of the build, consistent with the evolving thermal history of the process. These findings highlight a path for enhancing the process efficiency and energy utilization in additive manufacturing of tungsten.

A high-speed synchrotron radiography system has been developed to facilitate in situ imaging of dynamic processes in electron beam powder bed fusion (PBF-EB). Using the P61A White Beam Engineering Materials Science beamline at PETRA III, this system achieves high temporal resolution and a spatial resolution of approximately 10 µm. The scintillator screens are coupled to a diamond plate and housed within a specialized nitrogen gas cooling system, effectively mitigating thermal stress caused by the intense synchrotron beam. These innovative components ensure stable imaging performance and enhance the system's ability to operate under extreme conditions. By resolving fringes at short propagation distances for the partially coherent beam, the imaging system has enabled the efficient visualization of crack formation and pore evolution in high- Z materials, such as nickel-based superalloys, during the PBF-EB process. These advances not only optimize imaging in extreme environments but also open new avenues for high-energy synchrotron applications, including dynamic phase imaging and laser welding studies of dense samples.