Key Engineering Materials Vol. 1047

Abstract: Wire arc directed energy deposition (WA-DED) is a cost-efficient additive manufacturing process with high deposition rates, yet the prediction of resulting mechanical properties remains challenging due to repeated thermal cycling and associated microstructural changes. Accordingly, this work aims to validate a hardness prediction model for DIN SG2 by Härtel et al. For this purpose, a demonstrator was designed, manufactured, and simulated using a thermal finite element model in the standard software Simufact Welding 2025. Since the DED module of the software used does not adequately represent active interlayer cooling, four substitute models for the convective heat transfer coefficient were implemented and evaluated. In addition, the original hardness prediction model was refined to consider complex path planning, remelting effects and a material-dependent lower temperature limit for tempering or heat treating the material. Using a substitute model that adjusts the convective heat transfer coefficient over time, the improved hardness prediction the adjusted hardness prediction model achieved an accuracy of ±5% for 81 of 88 evaluated measurement points. In order to enable an efficient and reproducible comparison between simulation and experiment, a Python evaluation script was developed. This tool automatically identifies relevant temperature peaks, correlates them with hardness data, creates individual evaluation diagrams and a comparison diagram, and exports all processed data to an Excel file.

Abstract: Robotic additive manufacturing using pellet extrusion has gained significant scientific interest and industrial maturity. Increased part dimensions, reduced production time, and lower raw material costs are the main advantages of this process. This development has led to a strong demand for improved control and understanding of the process and of multiple phenomena occurring during fabrication. Consequently, process monitoring has received considerable attention, as it enables better understanding and detection of anomalies and their origins during manufacturing, allowing for immediate correction when possible or for more in-depth post-process analyses. Several studies in the literature have focused on monitoring parameters such as extrusion temperature, layer height, and printing speed to investigate their effects on final part quality and mechanical performance. In the present study, the objective is to quantify the forces applied to the deposited material during robotic additive manufacturing by pellet extrusion. This is made possible using a six-component force sensor, which allows the measurement of forces and moments along the three directions (X, Y, and Z). Following data acquisition, the results allowed understanding of force variations throughout the fabrication cycle and their correlation with the different stages of the manufacturing process. A single layer curve was explained with the corresponding peaks of each segment of the trajectory. It was found that at rounds there are peaks in Z forces due to the fact that, at the rounded sections, there is a slight accumulation of material, as the robot’s travel speed decreases while the material flow rate remains constant. This therefore results in higher applied forces. Consequently, it was observed that from the third layer onward, forces along the Z direction were almost no longer detectable. These measurements aim to facilitate the detection of manufacturing defects through unexpected force variations and to relate these observations to the final mechanical properties of the fabricated parts.

Abstract: Despite remarkable advances in additive manufacturing (AM), the uncertainty in direction-dependent strength and fracture behavior of metallic components still poses major challenges for their reliable structural application. The layered nature of laser powder bed fusion (LPBF) produces highly anisotropic textures and microstructure architectures that influence both plastic flow and fracture. While numerous studies have characterized tensile anisotropy, the coupling between build-induced anisotropy and stress-state-dependent fracture remains largely unresolved, yet it governs the structural integrity of AM parts under multi-axial loading. In particular, the extent to which anisotropy alters the ductile-to-brittle transition or fracture locus is still unknown. This study addresses this gap by combining experiments and advanced constitutive fracture modelling for two typical AM metals, austenitic 316L stainless steel and AlSi10Mg aluminum alloy. The goal is to formulate a unified, physically based description of anisotropic plasticity and fracture that is applicable across various material classes. LPBF samples of 316L stainless steel and AlSi10Mg were built at multiple orientations between 0° and 90° relative to the build direction. Uniaxial tensile tests were carried out with digital image correlation to capture full-field strain evolution and to determine r-values as a measure of plastic anisotropy. Complementary fracture tests under different stress states ranging from simple shear to plane strain tension were designed to evaluate the fracture dependence on stress states and anisotropy. It can be concluded that both alloys exhibit orientation-dependent flow and r-value during plastic deformation. The fracture strain decreases with rising triaxiality, yet its rate of decrease depends strongly on orientation, demonstrating a clear coupling between anisotropy and stress state.

Abstract: Laser Powder Bed Fusion (LPBF) of Inconel 718 (IN718) enables near-net-shape fabrication of complex components but is limited by narrow processing windows, crack susceptibility, and defect formation. In this work, the influence of substrate preheating on LPBF processability, densification, microstructure, and hardness of IN718 is investigated. Cuboid samples (10 × 10 × 10 mm³) were fabricated at three preheating temperatures (80 °C, 300 °C, and 500 °C), while laser power was varied between 100 W and 200 W with fixed layer thickness (30 µm) and hatch spacing (80 µm). Density was assessed using helium pycnometry and optical microscopy, while both optical and scanning electron microscopy (SEM) were used to characterize melt pool (MP) geometry, cellular substructure, cracking behavior, and oxide inclusions. Vickers hardness (HV10) measurements were performed to assess as-built mechanical response under high load of 10kg, whereas micro hardness under a load of 0.3kg was used to evaluate the hardening and/or softening phenomena occurring during LPBF processing. The results show that increasing preheating temperature significantly widens the full-density processing window, suppresses cracking, stabilizes MPs, and promotes partial in-situ ageing, leading to enhanced as-built hardness. Nevertheless, to high preheating temperatures appear to promote both the occurrence of large porosities and the formation of oxides inclusions. These findings highlight the need for preheating-aware LPBF process metrics beyond classical volumetric energy density.

Abstract: Of interest for military applications is the repair of damaged fastener holes on aircraft. One of the preferred repair processes, specifically for aluminum alloy 7075 (AA 7075), is friction stir additive manufacturing (FSAM) to avoid hot cracking and high residual stresses. Some of the largest challenges with this additive manufacturing process, however, are the high axial force requirement to deposit the consumable tool onto the substrate material as well as the amount of downtime necessary for repair. One possible solution is the utilization of electrical assistance during the FSAM process, since the yield strength of the alloy decreases with increasing current density when depositing bar stock. This work investigates utilizing electrically assisted friction stir technology on a conventional knee mill, which is commonly used in depots and machine shops, to showcase that repairs can be completed on commercial, commonly available equipment with decreased repair time. Varying current addresses an efficiency challenge of additive manufacturing by lowering the dwell time necessary for deposition. While higher current densities would address one of the largest concerns of FSAM – the high force requirements, the ability to repair holes using a retrofit conventional system would allow for more point-of-need applications. With the eventual application of military interest in mind, 7.95 mm (5/16”) diameter holes are drilled and repaired using FSAM via a conventional Bridgeport knee mill for use in typical machine shop locations. The material properties of AA 7075 stock material are compared to FSAM hole repairs completed with and without electricity incorporated.

Abstract: Varying boundary conditions, such as convection, radiation, and contact thermal exchange parameters in Directed Energy Deposition (DED) process modeling, can significantly impact the predicted thermal fields [1] and final properties of a product. The current numerical study analyzes the effect of different boundary conditions on the temperature distribution during DED thanks to a 3D model of AISI M4 tool steel validated by an experimental campaign. It also confirms that a 2D FE model can already provide valuable trends about sensitivity of numerical results to boundary conditions. The accuracy and robustness of the 2D and 3D model predictions are analyzed. The temperature histories of a set of points at different heights in the clad and the melt pool dimensions provide experimental validation.

Abstract: Additive manufacturing (AM) transforms automotive production by enabling lightweight, complex components with reduced material waste. The present contribution investigates multi-material AM for automotive demonstrators combining copper-manganese-nickel and copper alloys, leveraging their complementary structural, thermal, and electrical properties. Such a component from the automotive sector is benchmarked against the respective conventionally manufactured part. Key performance indicators include structural weight, manufacturing cost via Activity-Based Costing, production time, energy consumption, and CO₂ emissions. Although this investigation compares AM laboratory/semi-industrial-scale and conventional industrial-scale implementations, the multi-material AM can deliver significant system-level benefits in energy efficiency and vehicle performance. These advantages are realized despite existing challenges related to interfacial bonding and process integration, and notwithstanding the associated increases in weight, cost and carbon footprint.

Abstract: Additive manufacturing gains ground on the production of high-precision metallic components with varying thickness. As the material thickness alters in the various locations of the product, it is eminent that the material mechanical properties might vary. In the present contribution, a preliminary study was performed to investigate the resistance to fracture of additively manufactured AlSi10Mg material with varying thicknesses. To this end, fracture toughness specimens of compact tension geometry with varying thicknesses from 3 to 15 mm were additively manufactured, machined and tested. The results showed that with increasing the specimen thickness, critical stress intensity factor K_cr decreases gradually from 38 MPa√m up till 31 MPa√m for the lower and higher investigated thicknesses, respectively. Finally, it was noticed that even the 15 mm thickness (higher investigated) does not satisfy the plane strain fracture mechanism and therefore all investigated specimens were in plane-stress condition.

Abstract: Cross-contamination occurring after the blending of metal powders in multi-material laser powder bed fusion (PBF-LB/M) is a frequent manufacturing issue and poses a major obstacle to the further development of this emerging additive manufacturing process. To evaluate the influence of such contamination on a technologically important material system for multi-material PBF-LB/M, this study investigates the impact of CuCr1Zr foreign particle contamination within AlSi10Mg powder on the resulting metallurgical characteristics and mechanical performance of the fabricated parts. Several contamination levels of CuCr1Zr were considered, namely 0.5 wt.%, 3.0 wt.% and 5.0 wt.%, with the results benchmarked against samples produced from uncontaminated powder. Tensile testing demonstrated that the cross-contamination contribute to material embrittlement. This investigation focuses on the tensile work-hardening behaviour of the investigated materials showcasing that the specimens exhibit only the first two work-hardening stages, while for the higher contamination level studied, the material becomes brittle and fractures even in the first work hardening stage.