Elsa Wellenkamp Sequeiros

Micro-structured SAE H13 tool steel inserts for polymer injection molding require accurate replication of sub-millimeter features while retaining adequate densification and heat-treatment response. This study compared two powder-based routes on the same hemispherical insert containing pyramidal features of approximately 0.145 mm base width: hot embossing (HE) of water-atomized SAE H13 powder (supplier d50 = 5.7 µm, irregular morphology) compounded with a commercial M1 binder, and material extrusion (MEX) of a commercial gas-atomized SAE H13 filament processed on a Markforged Metal X. Rheological screening selected a 57:43 vol% powder-to-binder ratio for the in-house HE feedstock, and DSC/TGA measurements defined two-step debinding windows. The best HE conditions were 220 °C, 8 MPa, and 45 min for the in-house mixture, and 210 °C, 8 MPa, and 30 min for the granulated commercial filament; the latter showed a 0.15% linear deviation from the silicone replica diameter among the best-rated samples. Under the tested commercial MEX configuration, the pyramidal features were not resolved because the 0.40 mm deposition line width exceeded the target feature base width, causing the slicer to omit the sub-line-width geometry. The defect populations differed qualitatively: HE specimens showed porosity and local cracking associated with powder morphology and pressureless sintering, whereas MEX specimens showed build-direction-aligned inter-raster voids associated with the toolpath. Microhardness and tensile data are therefore interpreted as process-history-specific results rather than as a direct route ranking, because sintering conditions were not uniform across all specimens. The study defines an experimentally bound process-selection limit for SAE H13 micro-tooling: HE remains preferable for sub-nozzle surface features, whereas MEX remains attractive for macro-scale geometric freedom, if resolution, densification, and post-sintering consolidation are addressed.

Lead (Pb) is widely used in brass alloys (Cu–Zn) to enhance machinability, as its deformation into needle-like particles promotes chip breakage by initiating cracks. However, growing awareness of Pb’s toxicity has led to strict environmental regulations and growing demand for sustainable, lead-free alternatives. This systematic review, conducted following the PRISMA 2020 framework, consolidates recent research on the development and performance of machinable lead-free brass alloys. A comprehensive search was performed in the Web of Science, ScienceDirect, and Scopus databases, identifying 93 studies for full-text analysis. Various strategies have been identified for the development of lead-free brass, including process optimization, heat treatments, direct Pb substitution, and novel alloy design. The review highlights significant progress in achieving acceptable mechanical and machining performance, although trade-offs in cost, corrosion resistance, and large-scale manufacturability remain. The consolidated key findings offer a structured basis for future alloy design and promote consistent evaluation of microstructural, mechanical, and machining properties. Graphical Abstract

This study aimed to characterize a 316L stainless steel powder and a component produced from the same powder batch using the Laser Powder Bed Fusion (LPBF) process. SEM and EDS analyses, apparent density, tapped density, and pycnometric tests were conducted, alongside DSC and XRD analyses. The powders exhibited predominantly spherical morphology, with some variation in particle size and surface oxidation due to recycling and improper storage. Particle size distribution analysis using a Mastersizer 3000 revealed a fine powder fraction, with a median particle size (Dv50) of approximately 2?µm, significantly below the typical LPBF range. The crystalline structure of the powder was predominantly austenitic, with minor peaks that could correspond to ferrite or martensite. The component exhibited hardness values between 230 and 260 HV0.1, with a homogeneous distribution along both build and transverse directions. These results highlight the critical importance of powder condition monitoring for maintaining LPBF component quality.

The performance of Laser Powder Bed Fusion (LPBF) is highly dependent on the quality of the metallic powder feedstock. This study characterizes a gas-atomized Ti6Al4V (Grade 5) powder, analyzing morphology, particle size distribution, flowability, true density, chemical composition, phase constitution, and thermal stability. Optical and SEM imaging revealed predominantly spherical particles with some irregular shapes and satellites. Particle size analysis showed that only 46.49% of the volume fell within the specified 5–22?µm range, contributing to poor flowability (Hausner Ratio 1.86; Carr Index 46%). True density (4.35 g|cm³) closely matched the theoretical value, indicating low internal porosity. SEM|EDS confirmed the alloy composition but detected elevated oxygen levels. X-ray diffraction revealed an a-phase structure, while thermogravimetric analysis showed thermal stability up to 400?°C, followed by gradual oxidation. The results emphasize the critical influence of powder characteristics on LPBF processability and highlight the importance of stringent powder quality control to ensure reliable outcomes.

Smart textiles provide a significant technological advancement, but their development must balance traditional textile properties with electronic features. To address this challenge, this study introduces a flexible, electrically conductive composite material that can be fabricated using a continuous bi-component extrusion process, making it ideal for sensor electrodes. The primary aim was to create a composite for the filament’s core, combining multi-walled carbon nanotubes (MWCNTs), polypropylene (PP), and thermoplastic elastomer (TPE), optimised for conductivity and flexibility. This blend, suitable for bi-component extrusion processes, exemplifies the role of advanced materials in combining electrical conductivity, mechanical flexibility, and processability, which are essential for wearable technology. The composite optimisation balanced MWCNT (2.5, 5, 7.5, and 10 wt.%) and TPE (0, 25, and 50 wt.%) in a PP matrix. There was a significant decrease in electrical resistivity between 2.5 and 5 wt.% MWCNT, with electrical resistivity ranging from (7.64 ± 4.03)10⁴ to (1.15 ± 0.10)10⁻¹ Ω·m. Combining the composite with 25 wt.% TPE improved the flexibility, while with 50 wt.% TPE decreased tensile strength and hindered the masterbatch pelletising process. The final stage involved laminating the composite filament electrodes, with a 5 wt.% MWCNT/PP/(25 wt.% TPE) core and a TPE sheath, into a textile triboelectric impact detection sensor. This sensor, responding to contact and separation, produced an output voltage of approximately 5 V peak-to-peak per filament and 15 V peak-to-peak with five filaments under a 100 N force over 78.54 cm². This preliminary study demonstrates an innovative approach to enhance the flexibility of conductive materials for smart textile applications, enabling the development of triboelectric sensor electrodes with potential applications in impact detection, fall monitoring, and motion tracking.

Magnetic field-assisted control of magnetite location is a promising strategy for developing flexible, electrically conductive sensors with enhanced performance and adjustable properties. This study investigates the effect of static magnetic fields applied on thermoplastic elastomer (TPE) composites with magnetite and multi-walled carbon nanotubes (MWCNT). The composites were prepared by compression moulding and the magnetic field was applied on the mould cavity during processing. Composites were prepared with a range of concentrations of magnetite (1, 3, and 6 wt.%) and MWCNT (1 and 3 wt.%). The effect of particle concentration on composite viscosity was investigated. Rheological analysis showed that MWCNTs significantly increased the composite viscosity while magnetite had minimal impact, ensuring stable processing and facilitating particle orientation under a static magnetic field. Particle orientation and electrical conductivity were evaluated for the composites prepared with different particle concentrations under different processing temperatures. Magnetic field application at 190 °C enhanced magnetite/MWCNT interactions, substantially reducing electrical resistivity while preserving thermal stability. The composites showed no degradation at 220 °C and above, demonstrating suitability for high-temperature applications requiring thermal resilience. Furthermore, magnetite’s magnetic response facilitated precise sensor positioning and strong adhesion to polyimide substrates at 220 °C. These findings demonstrate a scalable and adaptable approach for enhancing sensor performance and positioning, with broad potential in flexible electronics.

Design for Additive Manufacturing (DfAM) is a transformative approach designed explicitly to optimize designs using metal additive manufacturing (AM). Exploring core DfAM principles, the chapter highlights the advantages of geometric freedom, material selection, and aligning designs with the capabilities of specific metal AM processes. It examines advanced optimization techniques like topology optimization and lattice structures to achieve high performance on lightweight metallic components. The transformative impact of metal DfAM is shown through real-world applications encompassing aerospace, healthcare, and automotive domains. The chapter acknowledges challenges inherent in metal DfAM, such as geometric limitations, surface finish considerations, and cost implications. Finally, it emphasizes the critical role of sophisticated software tools in driving design efficiency and explores future trends in AM metallic materials, technologies, and research.

Direct Energy Deposition (DED) is a highly efficient technology for the manufacture and/or repair of different components for multiple industries, including aeronautical. However, a good understanding of the various process variables is essential for producing deposits with the desired properties and ensuring process efficiency. In this study, the optimisation of Inconel 718 single-track deposits was carried out by varying laser power, scanning speed, and powder feed rate to minimise dilution and maximise height, always ensuring the efficiency of the process. The influence of the DED process’ inputs (laser power, scanning speed, and feed rate) and outputs (deposit’s geometry and dilution) were evaluated in the construction of Response Surface Plots and regression analysis equations, allowing the selection of the most promising processing conditions that achieve high-quality single tracks, with predicted dilution percentage, and deposit height. Optimisation analysis selected process parameters, and a block with 300 × 50 × 3 mm³ was built. Mechanical and microstructural characterisation of the built block before and after heat treatment (homogenisation at 1080 °C, followed by solubilisation at 980 °C, and double ageing at 720 and 620 °C) was performed through Optical Microscopy, SEM/EDS analysis, Vickers hardness and tensile tests. It could be observed that the chosen process leads to the formation of a dendritic structure with considerable amounts of Laves phase. However, heat treatments make it possible to obtain a more homogeneous structure with higher amounts of hardening phases, such as γ’ and γ”, which promotes an increase in hardness and tensile strength, and partial elimination of the Laves phase. With proper optimisation of the DED process and understanding of the different parameters’ influence on the deposit’s microstructure, it is possible to manufacture or repair Inconel 718 components for several industries.

While conventional die manufacturing techniques often lead to limitations in production speed and design intricacy due to labour-intensive procedures like machining and casting, Additive Manufacturing (AM) emerges as a key player offering substantial potential for cost reduction and process improvement in mass production. This study benchmarks four leading Laser Powder Bed Fusion (L-PBF) systems for producing maraging steel (EN 1.2709) dies. Despite the shared material and technology, variations in dimensional accuracy, surface finish, and microstructure were observed among the maraging steel parts. SEM/EDS, EBSD, hardness testing, and dimensional analysis revealed system-specific performance differences. Additionally, select parts underwent heat treatment and tensile testing, demonstrating the impact of post-processing on mechanical properties. These results offer valuable guidance for industrial stakeholders considering AM, highlighting the importance of supplier selection and process optimisation for achieving consistent part quality and unlocking the full potential of AM technologies.