Additive Manufacturing (AM), particularly electron beam powder bed fusion (PBF-EB), offers multiple advantages compared to conventional processing routes, but alloy development for AM is associated with high costs, as significant powder volumes must be produced and printed to enable mechanical property evaluation. This work evaluates whether conventionally processed substitute microstructures can provide meaningful mechanical property data for the early-stage screening of new AM alloy candidates. Substitute microstructures were produced from the γ′ Ni-based superalloys Alloy 247 and Alloy 247 LC using arc-melting, conventional casting, directional solidification, and controlled recrystallization, and were compared to two PBF-EB processed microstructures. Given the limited data on the recrystallization behavior in high γ′ Ni-based superalloys, a systematic recrystallization study was conducted to identify processing parameters capable of producing fine-grained microstructure with controlled grain boundary densities. Microstructural characterization was performed using scanning electron microscopy and electron backscatter diffraction. Compressive creep tests were conducted at 980 °C and 200 MPa. Although no substitute fully replicates the complex AM microstructure, selected microstructures exhibit comparable grain boundary characteristics and similar creep behavior in specific loading directions. Such well-controlled substitutes enable meaningful comparative creep testing and first-order extrapolation, offering a practical, resource-efficient route for early mechanical screening of new AM alloys.

Nickel aluminides reinforced with a ductile (Cr,Mo) phase are a novel class of high-temperature materials, promising a low density and good corrosion resistance. However, their ductility and creep strength are still limited. Additive manufacturing via electron beam powder bed fusion (PBF-EB) offers new opportunities for processing this material class: the high-temperature process is well-suited for processing crack-prone materials such as NiAl into near-net-shape geometries, and the high solidification rates create fine microstructures. In this study, we establish the first processing window for PBF-EB processing of a fully eutectic NiAl-(Cr,Mo) alloy and explore the effects of processing parameters on the microstructure and its evolution during the in-situ heat treatment characteristic of the process. The initial microstructure after melting exhibits a unique network-like, interpenetrating structure of NiAl and (Cr,Mo) phases. The size of the (Cr,Mo) phase increases with increasing energy input. Prolonged exposure to processing temperatures above 1000 degrees C leads to continuous coarsening of the phase network by a factor of 7, as well as discontinuous coarsening (DC). The DC reaction follows a Johnson-Mehl-Avrami-Kolmogorov pattern and stabilizes after several hours. The final fraction of discontinuously coarsened microstructure is determined by the choice of processing parameters. Furthermore, the DC reaction initiates at grain boundaries, thereby leading to grain refinement during coarsening. This refinement ensures a texture-free, fine-grained microstructure. Tuning the PBF-EB process parameters thus allows tailoring the microstructure of the NiAl-(Cr,Mo) alloy by selecting appropriate (Cr,Mo) phase sizes and DC fractions and provides a path to optimizing the alloy's mechanical properties.

In contrast to directionally solidified NiAl-CrMo in situ composites, additively manufactured specimens show a significant increase in the interface and cell boundary density. Understanding the resulting deformation structures in electron beam powder bed fusion processed NiAl-CrMo is important to optimize the creep performance. At lower temperatures of 700 degrees C and higher loads, the additively manufactured material exhibited a behavior consistent with power law creep, characterized by a notably high creep exponent. This suggests the dominance of dislocation activity, particularly the shearing of the CrMoss reinforcement phase within the composite, facilitated by knitting reactions of dislocations at the interfacial dislocation network. Conversely, at reduced loads and elevated temperatures of 800 degrees C-900 degrees C, the deformation mechanism shifted, as evidenced by inhomogeneous deformation and pore formation at vertical cell boundaries. In this regime, the climb of (001)-type dislocations was prevalent. The transition between these mechanisms appears to be strongly linked to the notably high density of cell boundaries after additive manufacturing. At higher temperatures, the shift towards a diffusive creep mechanism deteriorates the mechanical properties of additively manufactured NiAl-CrMo composites. However, exceptionally high creep strength is observed in the intermediate temperature regime, demonstrating the potential of additively manufactured NiAl-CrMo in situ composites.

In order to increase the productivity of the build process in electron beam powder bed fusion via spot melting, higher beam powers with larger melt spot sizes are commonly used. While these process modifications can improve productivity, they also lead to a coarser representation of the part's geometry. The current state-of-the-art countermeasure is to split the melt area into an infill area and a contour area. However, the split-up introduces challenges, such as an increased energy input, a transition area prone to defects, and the need for separate contour parameters. The proposed spot arrangements decouple boundary spots from the fixed lattice and combine this with stacking, i.e., lateral displacements between successively melted layers. While stacking reduces the risk of porosity in the infill, it also allows the contour to be processed simultaneously with the infill using the same beam parameters, thereby eliminating the defect-prone transition area. The benefits of the proposed approach are demonstrated on parts of varying complexity, supported by electron optical images, micrographs, and tactile roughness measurements.

The solidification behaviour of a tool steel is investigated during additive manufacturing (AM) with electron-beam powder bed fusion (PBF-EB). Solidification is controlled by thermal conditions and alloy composition. To study the impact of these two factors, high-speed operando X-ray diffraction (XRD) measurements of the PBF-EB process are performed over a wide range of processing conditions inducing cooling rates between 1400 K/s and 16000 K/s. The formation and transformation of the high temperature delta-ferrite phase are observed. The results reveal the dependence of the delta-ferrite presence time on cooling rates, providing insight into the impact of processing parameters on the delta-ferrite evolution. Furthermore, multi-component diffusion simulations are related to the experimental conditions accounting for elemental evaporation during PBF-EB processing. The simulations reveal the effect of compositional variations during the process on the solidification behaviour during PBF-EB processing. This work highlights the importance of understanding the interplay between processing conditions and alloy composition in PBF-EB, as well as how the combination of operando XRD with computational thermodynamics and kinetics tools can facilitate parameter and alloy development for the PBF-EB process.

Electron beam powder bed fusion (EB‐PBF) enables crack‐free Mo–Si–B alloys, yet the effect of postprocess annealing on microstructure and high‐temperature properties is not fully established. Here, EB‐PBF Mo–9Si–8B is annealed at 1200–1600 °C for 1–50 h and characterized by SEM/EBSD, quantitative image analysis, compression, and creep testing. The as‐manufactured state exhibits a very fine Mo ss dendritic network with interdendritic Mo 5 SiB 2 and Mo 3 Si. Annealing at 1200 °C largely preserves this morphology, whereas 1400–1600 °C treatments cause pronounced silicide coarsening. Phase fractions approach the 1600 °C Mo–Si–B equilibrium, and curvature‐driven parabolic growth is found for both intermetallics. Response‐surface modeling defines a practical processing window, where phase balance and morphology are near equilibrium. Compression tests between 1200 and 1400 °C reveal a transition from matrix/subgrain‐boundary‐controlled strength at 1200 °C to intermetallic‐controlled strength at 1400 °C. EB‐PBF Mo–9Si–8B achieves compressive strengths comparable to or above conventionally processed Mo–Si–B alloys. Creep tests at 1093 °C show that annealing at 1600 °C for 50 h reduces steady‐state creep rates partially by up to almost two orders of magnitude, demonstrating the effectiveness of tailored annealing for ultra‐high‐temperature applications.

In Electron Beam Powder Bed Fusion, the preheating step enables the processing of non-weldable materials by reducing thermal stresses. Additionally, the ongoing sintering creates a mechanically stable and conductive powder bed, preventing the formation of smoke and providing a beneficial basis for subsequent melting. The electron beam itself serves as an ideal heating device due to its high power and fast deflection velocities. The beam movement is typically performed according to the line order deflection pattern, with the aim of efficient, homogeneous and smoke-free heating and sintering. Given the multi-dimensionality of the parameters defining the preheating step and the deflection pattern, it is difficult to estimate the individual effects and dependencies, thus making it challenging to obtain the optimal setting.In this study, this issue is addressed by employing a numerical high-throughput approach to systematically explore how individual variations within the multi-dimensional parameter space influence the target quantities temperature and sinter degree. A total number of over 6000 relevant parameter combinations are evaluated to gather a comprehensive overview of the individual effects of the quantities line length, line offset, line order, beam focus, velocity and power. The results are presented in feature maps, facilitating clear identification of relationships and particular influences. Given the high fraction that preheating can take of the total layer time, the acquired understanding will have a significant impact on the efficiency of the process and the parameter selection.

Refractory Mo-Si-B alloys offer superior mechanical strength and oxidation resistance at elevated temperatures, making them promising candidates for next-generation turbine engines. Electron beam powder bed fusion (PBF-EB) enables the direct fabrication of complex components from such high-temperature materials. While a 〈1 0 0〉 || BD fiber textures is commonly expected in PBF-processed cubic metals, the as-built Mo-9Si-8B developed a pronounced 〈1 1 1〉 || BD fiber or near-random textures, depending on the area energy. We elucidate the role of post-solidification plastic deformation in governing texture evolution and recrystallization in the Mo solid-solution phase. Electron backscatter diffraction (EBSD) and thermo-mechanical simulations were combined to relate the local plastic strain to recrystallization and texture evolution. The final 〈1 1 1〉 || BD texture arises from collective lattice reorientation of the initial weak 〈1 0 0〉 || BD solidification texture, driven by plastic deformation (pencil-glide) under a biaxial tensile stress state. The recrystallized fraction scales with the local magnitude of plastic strain, consistent with the thermo-mechanical simulation predictions, confirming plastic deformation as the unifying factor behind both texture evolution and recrystallization. This work establishes a quantitative area energy – plastic-strain – microstructure framework, providing a mechanistic basis for tailoring crystallographic texture and recrystallization, thereby supporting property-oriented process design in PBF-EB processed refractory alloys.

Reliable microstructure control remains a major challenge in electron beam powder bed fusion, particularly for Ni-based superalloys such as IN718, where large columnar grains with a strong ⟨ 100⟩ texture cause highly anisotropic behavior, often limiting performance under unfavorably aligned or cyclic loads. Current approaches to achieve fine-grained, equiaxed microstructures focus on promoting a columnar-to-equiaxed transition by controlling the local solidification front velocity and the thermal gradient. However, this approach is highly material-specific, requires significant numerical verification and remains difficult to reproduce in complex parts due to the complex required temperature fields. For this purpose, spot melting enables the precise control of local energy input, thereby minimizing cumulative heating and enabling reproducible melt pool formation. In this study, we present a methodology for the experimental quantification of the spot melt pool shape and dimensions and examine how the melt pool geometry and the spatial melt pool arrangement influence the direction of the heat flux at the melt pool boundaries and, consequently, microstructure and texture evolution. By systematically varying the melt pool shape and the spacing between melt spots within a hexagonal lattice, we demonstrate the ability to generate a wide range of microstructures and textures, spanning highly anisotropic columnar microstructures with a ⟨ 100⟩ texture aligned along the build direction, fine-grained isotropic microstructures, and fine-grained, moderately anisotropic microstructures with a ⟨ 111⟩ texture aligned along the build direction, without invoking a columnar-to-equiaxed transition. This offers a promising outlook for complex parts, as it enables to locally choose between equiaxed microstructures and textures tailored to the desired loading direction, thereby further improving the performance of AM components.

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

Experimental observation of the dynamic melt pool evolution in advanced powder bed fusion processes is a challenging endeavor. The main challenge is that the small melt pool dimensions and its fast dynamic evolution require high spatial and temporal resolution of the monitoring equipment. Only dedicated, often costly experimental setups like high-resolution imaging or synchrotrons enable close-up views of the melt pool behavior. Multi-detector electron optical imaging enabled recently to determine the build surface topography in situ in layer-based monitoring scenarios in electron beam powder bed fusion. This study applies the method to study melt pool evolution. Detector signals during melting are recorded, with and without applied bias voltages on the detector plates. Furthermore, the dynamically evolving melt pool surface of single points is captured by fast electron optical imaging sweeps after beam is turned off. The imaging scan is also modelled using a mesoscopic Lattice-Boltzmann simulation tool to rule out possible melt pool distortions caused by scanning. Differences in melt pool evolution between experiment and model are observed. The developed method allows for observing melt pool dynamics with a previously unknown level of detail. It is envisioned that the method will allow for calibrating mesoscopic simulation models with experimentally measured dynamic melt pool properties.

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.

Combinatorial methods using composition gradients are valuable tools for the accelerated development of novel alloys. A key challenge for structural metals is ensuring specimens are large enough for representative microstructure and property development. Surface-laser-intermixing is a novel method that allows the synthesis of such specimens on the mm-cm scale while requiring only arc-melted feedstock. Herein, this method is applied for the investigation of a model superalloy system between Ni- and Co-based compositions with varying gamma '-fractions. The high energy input during remelting facilitates a melt pool depth of > 1 mm with only minor deviations of the compositions from the designed path through the system. The observed microstructure is in agreement with the literature-known phase stability. Microhardness measurements indicate the highest mechanical strengths in Nirich two-phase gamma/gamma ' compositions with medium to high gamma '-fractions. This study focuses on the methodological development of surface-laser-intermixing, limiting mechanical property assessment to microhardness. The results establish a basis for more comprehensive material library characterization in future work. A unique feature of this method is the inexpensive and time-efficient creation of large composition gradients and the large amount of data that can be obtained from the resulting materials libraries.

The multiphase alloy Mo-9Si-8B (at.

Electron beam powder-bed fusion processing of metals (PBF-EB/M) enables additive manufacturing (AM) of Ni-base superalloys at high temperatures above 1000 °C. Previous studies demonstrated the successful processing of CMSX-4 single crystals (SX). The SX selection process is based on standard grain selection combined with a stress-induced twisting of columnar grains around the build direction. This mechanism steadily merges different grains of various secondary orientations into one SX. The necessary anisotropic stresses are induced by the applied hatching strategy. Thus, changing the hatching strategy and therefore the stress orientation should also change the SX orientation. This study demonstrates how an AM single crystal is twisted around the building direction when the hatching strategy and thus the stress field are slowly rotated around the building direction with increasing build height. Electron backscatter diffraction confirms a continuous rotation of the secondary orientation over the build height following the applied hatch rotation. Thus, the orientation of single crystals can be specifically changed in the additive manufacturing process.

Fe-based BCC superalloys, composed of similar to two thirds Fe and Al by weight, offer a cost effective and sustainable solution for high temperature applications around 700 degrees C. Introducing Cu into alpha/alpha '/alpha '' superalloys can be used to tune lattice misfit and may contribute to enhance toughness and yield strength. However, understanding how Cu and its interaction with other elements affects the alpha/alpha '/alpha '' microstructure is crucial, as microstructural configuration significantly impacts creep resistance. This study investigates elemental partitioning, segregation, and Cu clustering in an Fe-Al-(Ni,Co)-Ti based alpha/alpha '/alpha '' superalloy containing 1.5 at.% Cu-originally added to improve toughness, inspired by prior ferritic steels. Atom Probe Tomography (APT) and Transmission Electron Microscopy (TEM) reveal that Ni, Al, Co, Ti, and Cu partition into alpha '/alpha '' precipitates. Within these, Cu segregates at former Anti Phase Domain Boundaries, where Co and Ti are locally depleted. Due to Cu's limited solubility in Fe and competition for Ni and Al sites, similar to 13.7 % and 33.0 % of Cu atoms cluster in the matrix and alpha '/alpha '' precipitates, respectively, while similar to 86.3% and 67% remain statistically distributed. Cu clusters show asymmetric size distributions: in primary alpha '/alpha '' precipitates, the most frequent and median sizes are similar to 14.3 nm and 23.7 nm; while in the matrix, where clusters co form with alpha ' precipitates, the most frequent and median sizes are similar to 2.4 nm and 42.0 nm. Additionally, two interfacial dislocation decorations are observed: one enriched with Co and Ti as Cottrell atmospheres and another with a Cu clusters "necklace". These findings offer critical insights for alloy and heat treatment design strategies aimed at balancing ductility and creep strength through controlled clustering and dislocation interaction.

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.

Electron optical (ELO) imaging has emerged as a powerful in-situ monitoring technique for electron beam powder bed fusion (PBF-EB). Until now, ELO imaging has been primarily used to analyze surface topography to detect defects such as porosity, cracks and bulging. However, the intensity of the ELO signal also depends on the composition of the material. In this work, element contrast is demonstrated by eliminating the influence of surface topography using a four-detector ELO system. The effectiveness of element contrast is demonstrated by monitoring alloy composition changes resulting from aluminum evaporation during the melting of squares on a titanium aluminide plate at room temperature. It is shown that the element contrast makes it feasible to extract the material-dependent ELO signal, even for highly bulged surfaces. Based on that, the method enables to detect changes in aluminum content due to evaporation, emphasizing the possible potential of a four-detector ELO system and the element contrast for in-situ aluminum evaporation detection for titanium aluminide alloys in PBF-EB.

Spot melting in electron beam powder bed fusion is a current research focus. This method exploits the ability of the electron beam to jump almost instantaneously between individual spots. This leads to an immense freedom in scan strategy design compared to line melting and opens up a wide range of unexplored strategies for robust processing of defect-free parts with tailored material properties. However, each layer of a part consists of thousands of spots ending up in an almost infinite number of possibilities to order them in a spot melting sequence. Common state-of-the-art approaches like random melting or pattern melting create a geometry independent, fixed spot sequence, thus do not use spot melting to its full potential. Planning a geometry-dependent spot sequence needs efficient algorithms due to the immense number of possibilities. In this work, we extend our graph-based, heuristic algorithm, which determines spot melting sequences on independent groups. The original approach is prone to failure, if the geometry contains areas far apart from each other or if areas are only connected via filigree regions. The proposed extension adds a subdivision of groups into communities thus taking advantage of the divide-and-conquer principle. The communities are ordered in a sequence by the approximate solution of the corresponding traveling salesman problem. With those additions, it is possible to determine suitable spot melting sequences for arbitrary geometries as long as the total number of spots per layer is high enough. We compare the algorithm with common spot melting strategies using a complex brake caliper geometry. Finally, experimental results including electron optical images and corresponding temperature simulations are presented.

Powder bed-based additive manufacturing allows the processing of demanding materials due to the high build space temperatures. In commercial machines up to 6 kW of power is available for the process, which is applied with a beam that can be moved almost without inertia. So far, such high beam powers have only been utilized to maintain the build chamber temperature, whereas the actual melting takes place at much lower power. This increases the time for melting as well as for heating and thus the overall process time. The aim of this study is to develop process strategies which enable a better utilization of the beam power and thus increase productivity. The resulting opportunities and challenges are exemplified with the Ni-base superalloy IN718.