Key Engineering Materials Vol. 1047

Abstract: High-velocity oxy-fuel spraying is a widely used thermal spray technology for producing dense and wear-resistant coatings. The thermal input during spraying strongly influences coating microstructure, residual stress state, and substrate integrity. In this work, in situ thermal measurements were performed on S235 substrates during High-velocity oxy-fuel deposition of 316L coatings. Two spraying strategies were compared: (i) single-pass rotation and (ii) multi-pass rotation. Thermocouples embedded at 1.8mm depth captured transient temperature responses, revealing significant thermal cycling effects. Single-pass operations produced no significant heating–cooling cycles, while multi-pass strategies led to thermal accumulation and overlapping cycles. The results provide reference data for the calibration of finite element heat source models and support the development of process–structure–property relationships in High-velocity oxy-fuel coatings.

Abstract: Architected metamaterials fabricated by additive manufacturing offer deterministic geometries and tunable mechanical properties that can outperform conventional foams in energy absorption and impact mitigation. In this work, origami honeycomb and plate-lattice metamaterial concepts are unified within a common, quantitatively characterised metamaterial. An optimization-based design approach is employed to maximise absorbed energy while keeping the peak stress below a predefined threshold, using metamaterial geometric parameters as design variables. The objective function is evaluated through post-processing of Abaqus compression simulations on automatically generated designs. Owing to the high computational cost, the optimisation is performed using an evolutionary algorithm with a limited number of evaluations, yielding a best-performing design rather than a global optimum. Despite this limitation, the results elucidate the critical roles of buckling in limiting initial peak stress and of contact in enhancing post-peak energy absorption, and they highlight the significant potential for further performance gains through expanded design space exploration.

Abstract: Additive manufacturing of polymeric foams via Material Extrusion (MEX) is an attractive route to lightweight components with tunable mechanical response. However, reproducible performance remains challenging because foam expansion, cell stabilization, and inter-layer bonding are strongly governed by the thermal–processing window. This study evaluates the feasibility of directly printing a commercial PLA foaming filament and quantifies the influence of nozzle temperature (and the associated flow-rate adjustment) on density and tensile behavior. ISO 527-2 tensile specimens were printed under three printing-condition combinations, a nominal PLA setting (190°C, 100% flow) and two foaming-window settings (250°C, 55% flow and 270°C, 50% flow). Tensile tests were conducted, and the tensile properties were assessed via Young’s Modulus, Yield and Ultimate properties (stress/strain), and elastic and total absorbed energy up to fracture. In addition to absolute values, all relevant metrics were normalized by relative density to enable robust comparisons across foaming levels. Finally, the DIC maps at the Yield and Fracture point were used to support the derived results and conclusions.

Abstract: The wire arc directed energy deposition (DED-Arc/wire) process offers great potential for the additive manufacturing of large-volume components thanks to high deposition rates and cost-effective plant technology. Aluminium matrix composites (AMCs) are a high-performance alternative to conventional aluminium alloys, but their use in additive manufacturing has been limited so far due to porosity, restricted mechanical properties and a lack of semi-finished wire products. This paper presents a resource-efficient inline process chain for the additive manufacturing of silicon carbide-reinforced (SiC) AMCs (AMC-SiC). Since commercial AMC-SiC welding wires are not available, an AMC-SiC wire was produced from an aluminium tube (AW-6060) filled with AMC-SiC chips by means of multi-stage rotary swaging to a diameter of 1.6 mm. The DED-Arc/wire welding tests carried out demonstrate the basic processability of the developed wire, but with pronounced porosity in the weld seam. By integrating an inline hot rolling process, the weld bead was significantly deformed and the porosity was significantly reduced, thereby expanding the application potential of additively manufactured AMC-SiCs.

Abstract: This paper presents an initial investigation into the numerical modeling of additive manufacturing processes for AlNiCo magnets. The research concentrated on calibrating the heat source parameters by utilizing previously published experimental results. The influence of laser power and scanning speed on the laser fusion of AlNiCo5 on SS 304 substrates was investigated through single track experiments. The geometries of the melt pools were measured and utilized as the foundation for model calibration. A two-step calibration methodology was adopted: (1) a simplified 2D model implemented in Octave was used for sensitivity analysis and parameter fitting; and (2) validation was performed using a 3D model within the commercial software Simufact Welding software. Parameters calibrated through 2D simulations could be directly transferred to the 3D context. However, while the calibration procedure enabled accurate fitting for individual tracks, it resulted in globally non-optimal parameters, suggesting that process parameters influence laser penetration depth.

Abstract: The growing demand for sustainable materials has driven interest in bio-based composites for additive manufacturing (AM). This study explores the feasibility of incorporating untreated coconut fibres into commercial photopolymer resins for stereolithography (SLA). Coconut fibres were extracted, processed, and integrated at varying concentrations into resin formulations, followed by fabrication of ASTM D638 Type IV specimens using a desktop SLA printer and UV post-curing. Mechanical characterization included tensile testing to assess Young’s modulus, tensile strength, and elongation at break, complemented by microscopy of fracture surfaces to evaluate fibre dispersion and failure mechanisms. Results indicate good compatibility between coconut fibres and photopolymer resin, with mechanical performance strongly influenced by fibre content. These findings highlight the potential of coconut fibre-reinforced photopolymer composites as sustainable alternatives for AM applications.

Abstract: Laser powder bed fusion (LPBF) parts are commonly fabricated using nominally uniform process parameters; however, local variations in thermal boundary conditions can significantly influence part quality. In this study, the spatial distribution of build-plate temperature during LPBF of Inconel 718 was experimentally characterized using a thermocouple grid, and its influence on porosity, microstructure and hardness was investigated. Despite a nominal build-plate set temperature of 180 °C, measured temperatures ranged from approximately 101 °C to 120 °C and exhibited a pronounced radial gradient from the center toward the edges of the build-plate. Cubic samples fabricated at locations corresponding to the highest and lowest local temperatures showed distinct microstructural differences, with higher temperatures promoting slightly coarser cellular–dendritic morphologies and lower hardness values. Although bulk volumetric porosity showed identical values for both locations (≈0.01 vol.%), the pore populations differed: the hotter location contained fewer but locally larger voids while the cooler location exhibited a higher number density of smaller pores, as shown by equivalent-diameter histograms and cumulative distributions. Samples produced at cooler locations exhibited finer microstructures and higher hardness. These results demonstrate that spatial non-uniformity in build-plate temperature can lead to local variations in microstructure and mechanical properties within a single LPBF build, highlighting the importance of characterizing local thermal conditions when establishing reliable process-structure property relationships.

Abstract: Triply Periodic Minimal Surfaces (TPMS) structures, such as the Gyroid, can exhibit nearly isotropic mechanical behaviour over specific relative density ranges, as predicted by the Zener anisotropy ratio. In contrast, the Laser Powder Bed Fusion (L-PBF) process may induce anisotropy in the material due to thermal gradients and residual stresses, potentially influencing the overall structural response. This work investigates how the anisotropy generated by the L-PBF process interacts with the inherent isotropy of Gyroid architecture. Gyroid lattices in 316L stainless steel were produced with varying unit cell sizes and wall thickness. Quasi-static compression tests were performed along directions parallel and perpendicular to the build axis to evaluate orientation effects. Numerical simulations, using both isotropic and anisotropic material properties, were employed to estimate the effective elastic response and the Zener anisotropy ratio. The combined experimental and numerical study aims to assess whether and to what extent the Gyroid architecture partially mitigates the transmission of process-induced anisotropy to the effective elastic response, contributing to a better understanding of the mechanical behaviour of additively manufactured metallic lattices. In particular, the study clarifies whether the theoretically isotropic Gyroid architecture is able to attenuate or transfer L-PBF-induced material anisotropy at the lattice scale.

Abstract: Conventional manufacturing techniques for continuous carbon fiber-reinforced polymers (CFRP) rely on costly, geometry-specific molds, which substantially limit design flexibility. To overcome these constraints, this paper proposes a robot-based, multi-axis Fused Filament Fabrication (FFF) approach for the production of CFRP components of complex geometries. The setup enables advanced material placement so that support structures and internal cores can be avoided, thereby reducing process preparation effort, post-processing requirements, and overall manufacturing cost. As a case study, a tee pipe geometry is investigated. A dedicated slicing strategy is developed in which the main pipe and the branching section are fabricated sequentially. This approach requires precise cutting and controlled re-adhesion of the CFRP material, a critical capability for extending conventional neat-polymer FFF processes to the additive manufacturing of CFRP. Experimental validation demonstrated the feasibility of the process, highlighting the critical role of an innovative technique called nozzle ironing for surface preparation, as well as the challenges associated with fiber cutting mechanisms. While the final component achieved structural coherence, leakage testing revealed porosity at specific interface regions, suggesting directions for future hardware refinement and process optimization.

Abstract: In today’s competitive manufacturing landscape, balancing cost and performance is crucial. Additive Manufacturing (AM) offers a path to efficient, functional designs, with Four-Dimensional (4D) printing emerging as a key innovation. By using materials that are responsive to external stimuli, 4D printing enables objects to change shape over time, making them active and opening new possibilities in adaptive design. Building on this, research into the shape morphing behaviour of 4D-printed objects was conducted through simulation. Based on the literature, this process can be effectively approached as a thermomechanical problem. This work first simulates the shape morphing of two-layer structures. Multiple parameters are varied through Finite Element Analysis (FEA) to assess both their independent influence and the feasibility of the proposed method. The study then analysed the use of orthotropic properties to evaluate control over deformation directions. Finally, insights from these phases were applied to more complex geometries. It is concluded that the morphing process can be computationally planned using a thermomechanical approximation, paving the way for the incorporation of the influence of printing parameters, pattern design and the strategic division into active/passive regions. This study provides foundational work in 4D printing regarding the shape prediction of printed objects.