Laser deep penetration welding of die-cast aluminum presents challenges as the presence of retained gas under high pressure leads to a modified spatial and temporal keyhole behavior, which determines conditions for process pore formation. Currently different investigation with the goal manipulating the keyhole behavior focus on the use of adjustable core-to-ring intensity distributions. In wrought materials, a core-to-ring intensity distribution is referred to advantage a broader melt pool and enhance the keyhole width especially on the top, while only few investigations on welding of aluminum die-cast are reported. In this paper, investigation with in situ high-speed synchrotron X-ray imaging of a deep penetration laser welding process involving die-cast aluminum with different core-to-ring intensity distribution are presented. The results highlight a broadening of the keyhole width in the core-dominated process, while in the ring dominated process the keyhole width on the top is strongly reduced, leading to a pronounced bulging on the bottom of the keyhole. Further in the core-dominated process a second separated channel is formed beginning from the tip of the keyhole growing then in the rear part of it. This is then responsible for formation of a non-spherical cavity in the solidified pool. In the case of a ring-dominated regime bulging is occurring with mainly large bulging pores forming.

We present F3CT, a synchrotron-based hyperspectral full-field fluorescence computed tomography technique that avoids raster scanning by combining a pinhole aperture with an energy-resolving 2D detector. A virtual cone-beam model and two-stage calibration-reconstruction workflow enable 3D elemental mapping under full-field illumination. The method is demonstrated on biological and geological specimens, resolving silver-stain distributions in zebrafish tissue and high-energy fluorescence signatures in rock cores. Phase-contrast tomograms acquired sequentially under the same experimental geometry provide co-registered structural context. F3CT provides a high-throughput route to 3D XRF imaging and establishes a foundation for correlated structural and chemical tomography, with potential for future in-situ and operando implementations.

Additive manufacturing (AM) enables the precise fabrication of multimaterial components; however, Achieving chemical and structural homogeneity at material interfaces remains a significant challenge. Existing research on material transport in AM primarily relies on numerical simulations and postmortem analyses, with realtime, three-dimensional characterization still lacking. In this study, we employ in situ X-ray radiography and X-ray computed tomography to investigate material redistribution during laser powder bed fusion of a Al-CuCrZr multimaterial. Our results demonstrate that the incorporation of Cu occurs through discrete, stochastic events within the melt pool. We suggest that this mode of incorporation results from the poor wetting of the spreading liquid on the substrate liquid, necessitating additional dynamic driving forces to assist the incorporation process. Within the melt pool, copper mixing is predominantly governed by fluid dynamics, with relatively negligible effects from gravitational/buoyancy and viscous forces, as well as diffusion. However, despite the high fluid velocity, heterogeneous local compositions persist. These variation of local composition, in turn, lead to shifts in the local solidification path and ultimately influence the resulting microstructure. The predominant mixing mechanisms and length scales are likely applicable to a wider range of multimaterial systems. Additionally, the incorporation mode could be expected to hold for multimaterial systems sharing similar wetting behavior, but requires further investigations for confirmation. These findings offer valuable experimental validation for numerical models and provide key insights to guide the optimization of future multimaterial AM processes.

Pulsed laser beam welding is widely used to weld thin aluminium alloy sheets, for example, in e-mobility components such as prismatic battery casings. However, aluminium alloys are prone to hot cracking phenomena during solidification, which is affected by different factors. In pulsed laser welding, the solidification rate is highlighted as a key factor, while tensile strain development during solidification shrinkage must also be considered a dominant factor leading to hot cracking. Accurate temporal strain measurements preceding hot crack initiation during solidification remain challenging to obtain, especially beneath the welding surface. Therefore, a thermomechanical finite element model is developed in ANSYS software to simulate time-dependent strain evolution at different depths around the melt pool during solidification. The simulation results are compared with experimental results of time-resolved high-speed synchrotron X-ray diffraction (XRD) measurements beneath the welding surface. The finite element model accurately captures the overall strain evolution and peak strain magnitudes observed experimentally, demonstrating good agreement in terms of global strain trends. Additionally, the time-dependent strain measurements reveal distinct strain-drop times corresponding to crack initiation at different time lags and to crack propagation from the melt pool boundary.

In situ synchrotron studies of Directed Energy Deposition (DED) additive manufacturing provide unique process insights, using high-resolution spatial and temporal observations to reveal melt pool dynamics, phase evolution, and defect formation mechanisms. However, capturing these phenomena under industrially relevant conditions remains a challenge. Here, a second-generation DED apparatus is presented that replicates industrially relevant process conditions whilst enabling multi-modal in situ monitoring, including synchrotron X-ray radiography and diffraction, infrared (IR) imaging, inline coherent imaging (ICI), and optical imaging. The equipment, termed the Blown-powder Additive Manufacturing Process Replicator-II (BAMPR-II), also facilitates a range of unique process adaptations including the application of heat, magnetic fields, and ultrasound. Two case studies are described demonstrating how BAMPR-II reveals the underlying phenomena controlling DED, including: (1) simultaneous X-ray and ICI imaging to capture cracking mechanisms during DED; and (2) X-ray imaging of DED illustrating how magnetic fields can control flow in the melt pool.

Additive manufacturing by Powder Bed Fusion using a Laser Beam on Metals (PBF-LB/M) enables unprecedented design freedom but remains limited by defect formation that stems from unstable melt pool dynamics. Current monitoring approaches often depend on machine learning, which can obscure the underlying physics and complicate industrial deployment. Here, a direct acoustic emission-based methodology is introduced that captures sound signatures of conduction-keyhole transitions and keyhole collapse. Using acoustic emission measurements validated by operando synchrotron X-ray imaging, a series of envelope-based indicators are established that robustly distinguish stable and unstable regimes in 316 L steel and Ti6Al4V under continuous and pulsed lasers. This physics-driven framework provides transparent, localized regime prediction, paving the way for more reliable and industrially scalable monitoring solutions in metal additive manufacturing.

Laser Additive Manufacturing (LAM)-induced directional solidification creates complex microstructures in nickel-based superalloys, featuring columnar grains with cellular sub-grains and carbides. Using Scanning 3D X-ray Diffraction (S3DXRD), we reveal orientation and intergranular strain relationships coupled to cellular sub-grain networks and primary cubic MC carbides. We analyzed 3D orientation and elastic strain fields across 82 γ grains and 37,000+ carbides in an ABD-900AM alloy produced via Directed Energy Deposition (DED). Cooling-induced solute segregation creates volumetric lattice parameter patterning in the γ phase, altering residual stress fields. Ti-, Ta-, and Nb-rich carbides form preferentially in these high-solute regions, exhibiting weak orientation relationships with parent γ grains. These results provide the first non-destructive 3D study linking rapid solidification segregation, deformation heterogeneity, and carbide architectures in additively manufactured Ni-superalloys. These insights provide crucial detail to rationalise LAM process parameter optimisation and the coupled spatially governed structural performance. Researchers present a highly detailed, synchrotron resolved, 3D microstructural investigation of how tiny structures/defects form inside nickel superalloys during metal additive manufacturing, with the goal of helping engineers build tougher jet engines and turbine parts.

The goal of this work is to understand melt pool dynamics and material mixing in Multi-Material Laser Powder Bed Fusion (MM-LPBF), with particular emphasis on the influence of spatter formation at the distinct-material interface. The ability to selectively process steel-copper materials with finer resolution and greater design complexity in LPBF is of significant interest to the aerospace, nuclear, and structural industries because it enables the fabrication of components with both high strength and thermal performance. However, the understanding of melt-pool dynamics near interfacial regions in MM-LPBF remains limited, affecting the mixing zone and ultimately the interface properties. In this work, an in-situ X-ray synchrotron operando setup is used to investigate the melt pool evolution during MM-LPBF of bronze (Cu10Sn) and stainless steel 316L. Computational fluid dynamics simulations complement the X-ray observations by analyzing thermal evolution, laser-metal interactions, and material mixing. The results show that spatter ejection disrupts melt pool stability, producing heterogeneous mixing characterized by elongated, abrupt islands in the interfacial region. Unlike single-material LPBF, MM-LPBF with dissimilar alloys that have markedly different thermal properties and laser energy absorptivity results in non-steady melt-pool dynamics that promote process instabilities and spatter formation. This work is the first to investigate the spatter formation mechanism in MM-LPBF using in situ X-ray analysis and provides new insights into process limitations by demonstrating that the standard laser beam profile is insufficient to effectively control material mixing at the interface.

The characterization of metal powders is crucial for assessing their suitability in additive manufacturing applications. Synchrotron X-ray computed tomography provides high-resolution, three-dimensional data for evaluating particle morphology and internal porosity. However, accurate interpretation of such datasets, particularly for metallic powders, remains challenging due to reconstruction artifacts and segmentation sensitivity. This study presents an optimized post-reconstruction segmentation framework using marker-controlled watershed implemented using Fiji, aimed at improving robustness and reproducibility in synchrotron-based powder analysis. Aluminum alloy powders sieved to less than 150 mu m and less than 100 mu m were analyzed to investigate the influence of image quality, filtering, and marker definition on segmentation outcomes. The finer powder sample, affected by noise voxels, required a two-step adaptive filtering strategy and careful tuning of the contrast threshold based on the distance map, using the h-parameter in the extended maxima function. In contrast, the coarser sample, exhibiting minimal noise, showed stable segmentation performance across a broader range of threshold values. Morphological metrics such as Feret diameter and Equivalent Spherical Diameter were employed to evaluate the accuracy of segmentation and particle shape. Results indicate that dataset-specific preprocessing and distance-driven marker definition are essential for minimizing under-and over-segmentation in noise-affected data. The proposed framework enhances the reliability of synchrotron X-ray computed tomography-based powder analysis, supporting its use in quality control of feedstock materials for additive manufacturing.

This study investigates various cracking mechanisms and their prevalence in fusion processing of steel-copper multi-materials using operando X-ray diffraction and imaging during laser powder-bed fusion (LPBF) of 316L-CuCrZr multi-material. During this investigation, three main types of cracking were identified: (i) solidification cracking, (ii) metal-induced embrittlement (MIE), and (iii) liquation cracking. All cracking types are closely related to phase formation during processing and stem from two underlying mechanisms. First, liquid-liquid phase separation (LLPS) and the monotectic reaction in the 316L-CuCrZr system cause two liquids with vastly different solidification ranges to form, leading to solidification cracking. Second, LLPS and the monotectic reaction uniformly distribute Cu-rich liquid between the Fe-rich dendrites, leading to MIE and/or liquation cracking. Conducted based on the insights gained from the operando characterisation, further experiments showed that cracking can be drastically reduced by avoiding phase separation. However, the complete elimination of cracking necessitates chemical alterations in the material feedstock, indicating that while process adjustments can mitigate cracking, they may fail to fully prevent it. These findings serve as a guideline for understanding the underlying causes of cracking in steel-copper multi-materials, how process optimisation can effectively mitigate cracking, and to what extent such adjustments in processing can achieve this outcome.

Understanding the microstructural formation and evolution in a dynamic temperature field during the metal additive manufacturing process has been a significant challenge, particularly in alloy systems containing solute (s) with high diffusivity at temperatures where solid-solid phase transformations take place, such as the eutectoid decomposition in Ti-Cu alloys. This study explores the influence of the build process on the microstructural evolution in Ti-8.5Cu alloy processed using Directed Energy Deposition - Laser Beam/Metals (DED-LB/M). Utilising in situ synchrotron X-ray radiography, changes in melt pool geometry for each layer during the DED-LB/ M process are analysed. The results reveal a substantial increase in the length, depth and volume of the melt pool from the bottom to the top layers and with the increase of laser power. Such changes reflect the rise in residual temperature, and these data are used to calibrate the classical Rosenthal model, enabling it to accurately describe the temperature profile across the entire build. Post-build electron microscopy studies reveal that the volume fraction of pearlite exhibits an unusual 'V-shaped' dependence on laser power. This dependence is well explained by the competition between the nucleation rate and the growth rate of pearlite. This finding offers valuable insight into microstructure manipulation of Ti-8.5Cu alloy during DED-LB/M processing. It also serves as an excellent example of how in situ synchrotron X-ray imaging can be fully utilized to understand microstructure evolution in a complex and challenging manufacturing process.

Spatter formation is a major issue at welding speeds above 8 m/min for full penetration laser beam welding of high-alloyed steels. In experiments using a local gas flow directed at the keyhole rear wall, a reduction in spatter formation on the specimen top side was observed for welding of AISI 304. However, the interaction between gas flow and keyhole behavior with respect to the mechanisms and locations of spatter detachment, especially on the bottom side, is not yet fully understood. High-speed synchrotron X-ray imaging enables detailed insights into the keyhole behavior and the spatter formation to obtain a deeper understanding of the underlying mechanisms. During the reference experiments welding without shielding gas flow, the spatter detach from a melt pool swelling behind the keyhole aperture on both sides of the sheet. A gas flow with a low flow rate of 4.8 L/min reduces the spatter formation on the top side and the keyhole length due to the absence of oxygen affecting the surface tension. A swelling also forms on the keyhole front on the bottom side and small spatter detach undirected. Increasing the flow rate to 12.8 L/min elongates the keyhole, particularly on the specimen top side. The increased momentum transfer of the gas flow results in a periodic keyhole oscillation on the specimen top side. In combination with an elongated melt pool, the oscillation is directly correlated with the hump formation, caused by melt being pushed over the already solidified weld seam. In addition, spatter does not detach from the top side due to the changed melt flow and only detach from the keyhole front on the bottom side.

The high melting temperature of tungsten (W) makes it an attractive candidate for energy generation applications; however, its use is limited by its poor ductility at low temperatures. This limitation affects even melt-based additive manufacturing (AM) processes such as laser powder bed fusion (PBF-LB), with as-fabricated pure W exhibiting both longitudinal and transverse cracks. Metallurgical and processing factors that affect these cracks are still being explored. This work utilizes powderless single-tracks on pure W plates made over a range of power and velocity combinations in three unique PBF-LB setups: one with flowing argon, one with continuous vacuum, and an in situ high-speed synchrotron X-ray radiography setup. Each had different oxygen activities in their build environments. Longitudinal cracks with oxides appearing to exude from the crack were found for tracks deposited in a build environment with argon shield gas, while no such cracks were observed for builds conducted in vacuum. A calculation showed that direct oxygen ingress into the melt pool from the build environment is negligible when argon shield gas is present. Thus, incorporation of spatter is a likely mechanism for oxygen ingress into the melt pool. Radiography showed extensive keyholing, spatter generation, and crack formation at keyhole porosity. A heat transfer calculation showed the crack formation time was consistent with cooling below its ductile-to-brittle transition (DBT) temperature. This work identifies solidification cracking as a feasible mechanism in pure W beyond the well-known DBT related cracking.

This paper examines the impact of spatial power distributions on the time-dependent keyhole behavior during laser beam welding of copper using high-speed synchrotron X-ray imaging. The experimental setup utilized a COHERENT HighLight FL8000-ARM fiber laser with concentric intensity distribution created by an optical fiber cable. The European Synchrotron Radiation Facility (ESRF, beamline ID19) was used to conduct high-speed synchrotron imaging at 20,000 images per second to study the spatio-temporal keyhole behavior. Keyhole geometries were extracted through advanced image processing techniques, allowing quantification of parameters like depth, aperture, bulging, and determination of related oscillation frequencies. The results showed that core-dominated processes exhibit significant variations in keyhole geometry. In contrast, ring-dominated processes exhibited reduced penetration depths but increased melt pool dynamics due to altered absorption conditions and increased temperatures within the melt pool. A stabilized core-ring power distribution minimized fluctuations, resulting in improved process stability. The findings were summarized in a model concept describing three characteristic keyhole regimes: core-dominated, ring-dominated, and stabilized core-ring processes.

This study investigates the cracking mechanism in additive manufacturing of Ni-Cu multi-material combinations using operando X-ray diffraction and imaging experiments during laser powder-bed fusion (L-PBF) of CuCrZr and IN625. It is shown that liquid immiscibility between the two alloy systems stems from the interaction between Cu and the alloying elements in IN625, causing both Cu-rich and Ni-rich liquids to form with different freezing ranges. Consequently, solidification cracking takes place due to the large solidification range where the Ni-rich solid and Cu-rich liquid co-exist. Guided by thermodynamic calculations, it was identified that the highest crack susceptibility occurs between 20 and 40 wt% CuCrZr-IN625, which was further validated by printing mixtures of the two alloys in different ratios. Operando X-ray imaging and scanning electron microscopy characterization revealed that the cracking occurred during the terminal stage of solidification. It was observed that the columnar grains of the Ni-rich primary solid separate into cracks, where Cu-rich liquid regions persist over a wide temperature range as the solidification of these regions begin significantly later. It was concluded that the mechanism of cracking explained in this study could be extended to other Cu-Ni alloy combinations containing elements that induce immiscibility when mixed with Cu during fusion-based processing methods.

Porosity in directed energy deposition (DED) deteriorates mechanical performances of components, limiting safety-critical applications. However, how pores arise and evolve in DED remains unclear. Here, we reveal pore evolution mechanisms during DED using in situ X-ray imaging and multi-physics modelling. We quantify five mechanisms contributing to pore formation, migration, pushing, growth, removal and entrapment: (i) bubbles from gas atomised powder enter the melt pool, and then migrate circularly or laterally; (ii) small bubbles can escape from the pool surface, or coalesce into larger bubbles, or be entrapped by solidification fronts; (iii) larger coalesced bubbles can remain in the pool for long periods, pushed by the solid/liquid interface; (iv) Marangoni surface shear flow overcomes buoyancy, keeping larger bubbles from popping out; and (v) once large bubbles reach critical sizes they escape from the pool surface or are trapped in DED tracks. These mechanisms can guide the development of pore minimisation strategies.

Laser beam welding with partial gas shielding using local gas flows has been shown to be very effective in reducing spatter, especially when welding high-alloy steels at high processing speeds (>= 8 m/min). This paper examines the gas flow induced mechanical effect on keyhole geometry and correlating melt flow by means of a computational fluid dynamics analysis. Therefore, keyhole mode laser beam welding of AISI304 was modeled by using the volume of fluid method in FLOW-3D. The mechanical effect of the partial shielding was implemented by considering the gas flow induced dynamic pressure. By varying flow rates, a widening, and a reduction in fluctuation amplitude of the keyhole rear wall was detected. Furthermore, the melt flow dynamics were characterized by less flow velocity and melt movement. The results were validated by a visual comparison with high-speed synchrotron X-ray imaging, showing a high degree of agreement in modeling accuracy of the keyhole dynamics. (c) 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)

The columnar grains in additively manufactured alloys increase the tendency to form solidification cracks and cause anisotropy. Studying the effect of process parameters on microstructure development helps to guide the manufacturing of the equiaxed grain microstructure. First, the effect of process conditions on the melt pool dimensions using in situ synchrotron X‐ray imaging and thermal profile and solidification condition using finite element simulation and calculation of thermodynamics phase diagrams of CrMnFeCoNi high‐entropy alloy fabricated by directed energy deposition is studied. Increasing the laser power reduces the thermal gradient to solidification rate ratio, pushing the solidification closer to the columnar‐equiaxed transition. Nevertheless, the simulations still indicate the columnar microstructure for all scan conditions in contrast to the experimental observation that shows single‐wall samples built at 200 W consisted of dominantly equiaxed grains, whereas columnar grains are dominant in samples built at 100 W. It is believed that in addition to the effect of thermal gradient and solidification rate, the chemical segregation (Mn and Ni) during solidification may promote dendrite detachment, hence assisting the transition to equiaxed grains. The multitrack deposition results in more solid beneath a new melt pool, increasing the thermal gradient that promotes more columnar grains in comparison to single tracks.

AbstractCracking during Laser Additive Manufacturing is a problem for many higher-strength aluminium alloys, including AA6061. Here, we used a pulsed laser with ramp-down power modulation to improve the cracking resistance by about 50% compared to the use of a rectangular pulsed laser. Using synchrotron in situ X-ray imaging at 100,000 images s−1, ground truth data was obtained about changes in melt pool geometry, solidification rate, and thermal gradients were calculated. An analytical hot cracking model was developed to show that these changes lead to a decreased hot tear susceptibility. Therefore, laser pulse modulation can be an effective tool to reduce crack susceptibility of alloys. More fundamentally, the results demonstrate that modifying thermal conditions provides a pathway to crack elimination in LAM and the model established in our study sets the foundation for further complex laser manipulation in modifying the printability and resulting mechanical properties of hard-to-process alloys in Laser Additive Manufacturing.

Laser welding zinc-coated steels is of major importance in automotive engineering and other industries to ensure cost-effective corrosion resistance of assemblies without requiring post-weld rework. However, the low evaporation temperature of zinc is causing welding defects, in particular melt ejections and spatter. In this work, in-situ experiments of laser beam welding were performed using high-speed synchrotron Xray imaging (up to 40,000 images/second) to determine the dynamics in the keyhole and in the weld pool and to provide detailed explanations for the formation of weld defects. A simplified sample geometry made it possible to weld zinc-coated steel sheets (DX51D Z275) in a lap joint (sheet thickness 1.25 mm each) with a fiber laser (COHERENT HighLight FL-ARM 8000) to describe fundamental phenomena. The high spatial and temporal resolution of the radiography allowed describing the acting mechanisms and their effect on keyhole and melt pool. (c) 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)