Search Results (362)

Additive manufacturing (AM) enables the consolidation of components and the integration of new functionalities in metallic parts, but layered fabrication often results in poor surface quality and geometric deviations. Among various surface treatment techniques, machining is often favoured for its capability to enhance not only surface finish but also critical geometric tolerances such as flatness and circularity, in addition to dimensional accuracy. However, machining AM components, particularly thin-walled structures, poses challenges related to unconventional material properties, complex fixturing, and heightened susceptibility to chatter. This study investigates the vibrational behaviour of thin-walled Ti6Al4V components produced via laser powder bed fusion, using a jet-engine compressor blade demonstrator. Four stock envelope designs were evaluated: constant, tapered, and two topologically optimised variants. After fabrication by Laser Powder Bed Fusion, the blades underwent tap testing and subsequent machining to assess changes in modal characteristics. The results show that optimised geometries can enhance modal performance without increasing the volume of the stock material. However, these designs exhibit more pronounced in situ modal changes during machining, due to greater variability in material removal and chip load, which amplifies vibration sensitivity compared to constant or tapered stock designs. Full article

Catalytic ozonation has been widely utilized in environmental applications, such as the removal of pharmaceutical active compounds (PHACs) from wastewater, due to its outstanding catalytic efficiency. To further enhance its performance and expand its practical application, ozone-based hybrid processes have been investigated, including ultraviolet radiation/ozonation, hydrogen peroxide/ozonation, ultrasonication/ozonation, and biological treatment/ozonation. Ozone degrades pollutants via two primary pathways: direct oxidation (via molecular ozone) and indirect oxidation (via reactive intermediates). Enhancing ozone decomposition into various reactive oxygen species (ROS), predominantly hydroxyl radicals, can significantly augment the degradation efficiency of pollutants. The surface adsorption and electron transfer processes of catalysts can promote ozone activation and decomposition into ROS to achieve the efficient degradation and mineralization of pollutants. Among catalysts, Mn-based catalysts have been extensively studied in past research. They have demonstrated exceptional performance when combined with other metals, such as Mn/Ce, Mn/Fe, and Mn/Co, etc., due to synergistic effects arising from bimetallic interactions. The inherent characteristics of catalyst supports may also influence the generation process of ROS. Choosing an appropriate support is conducive to promoting the uniform distribution of catalytic active sites on the catalyst surface and avoiding the agglomeration of metal particles, and it is also beneficial for the recovery and reuse of the catalyst. Furthermore, coupling catalytic ozonation processes with techniques like high-gravity technology, jet reactor systems, and micro–nano-bubbles can improve the utilization efficiency of ozone by exploiting gas cavitation effects. In this paper, we summarize the research progress in the degradation of PHACs using catalytic ozonation and discuss strategies for improving the mass transfer efficiency of ozone in water. Finally, the challenges and opportunities associated with applying catalytic ozonation in practical applications are also discussed. Full article

Aluminum (Al) powder with low sinterability is difficult to use in binder jetting (BJT) additive manufacturing, which involves sintering a metal powder after forming a green body. A liquid-phase sintering process for Al powder using Al–Cu eutectic alloy powder as a sintering aid has recently been developed. In this study, to clarify the applicability of liquid-phase sintering to BJT additive manufacturing, the effect of the initial relative density of green bodies (ρ_rel,0 = 50–90%) on the final relative density was investigated. The final relative density was not significantly affected by ρ_rel,0 and achieved 96–97% after sintering at 630 °C for 1800 s. However, pores are likely to remain in the sintered body with a high ρ_rel,0 of 90%. In situ observations using synchrotron radiation X-ray computed tomography revealed that large pores were formed at the early sintering stage of the green body with ρ_rel,0 of 90% and partially retained after sintering. By contrast, the green body with ρ_rel,0 of 50% exhibited a significant rearrangement at the early sintering stage, promoting the densification. This study provides a deep understanding of liquid-phase sintering of Al powder, which is considered a suitable post-processing method for BJT additive manufacturing. Full article

Recent global efforts to produce lightweight electrified vehicles have motivated the push toward advanced lightweight materials which led to the creation of novel alloys optimized for use in high-pressure die casting (HPDC). HPDC enables the fabrication of near-net-shape automotive parts, significantly reducing or eliminating additional machining steps. A key feature of HPDC is the extremely fast cooling that forces the alloy to solidify within only a few seconds. Because of these rapid cooling conditions, it becomes essential to accurately evaluate the thermophysical behavior of newly designed lightweight alloys during severe quenching. Precisely quantifying these material properties is crucial for properly controlling HPDC operations and for building reliable numerical models that simulate filling and solidification. The thermophysical characteristics of such alloys vary markedly with temperature, especially when the material undergoes the fast solidification typical of HPDC. Therefore, understanding how these properties change with temperature during intense cooling becomes a critical requirement in alloy development. To address this need, a dedicated experimental system was designed to solidify molten metal samples under controlled and variable cooling conditions by applying multiple impinging water jets. An inverse heat-transfer algorithm was formulated to extract temperature-dependent thermal conductivity and diffusivity of the alloy as it solidifies under rapid cooling. To verify the reliability of both the inverse model and the measurements, experiments were performed using pure Tin, a reference material with well-documented thermophysical properties. The computed thermophysical properties of Tin were benchmarked against values reported in the literature and demonstrated reasonable consistency, with a maximum deviation of 13.6%. Full article

This Special Issue presents recent advances in the production, modelling, processing, and characterization of advanced industrial materials, highlighting the diversity and sophistication of contemporary research discussing metallic, polymeric, composite, and nano-structured systems. The collected contributions address key challenges in materials science, ranging from surface quality control, the development of novel machining and fabrication tools, and optimization of thermoplastic composite consolidation, to provide fundamental insights into additive manufacturing, rheology, and constitutive modelling. The showcased studies introduce innovative approaches to metrology, including advanced optical, fluorescence, and X-ray scattering techniques for characterizing nano-particles, microstructures, and thermal properties. The presented research also features investigations into the welding of dissimilar steels, binder jetting of stainless steel, and the influence of heat treatment on functional steel performance, alongside environmentally oriented research on natural-fibre energy devices and bio-based polymer composites. Further research topics include defect structures in doped crystals, low-temperature synthesis of oxide films, and mechanical behaviour of steels under extreme conditions. Collectively, these articles demonstrate the strong synergy between experimental methods, computational modelling, and industrial applications, underscoring the continued progress in materials reliability, surface engineering, and advanced manufacturing technologies. This Special Issue therefore provides a comprehensive overview of current trends and emerging directions, offering valuable methodological and conceptual insights in the field. Full article

Additive manufacturing (AM), commonly known as 3D printing, is revolutionizing modern dentistry, introducing high-precision, patient-specific, and digital-driven workflows across prosthodontics, orthodontics, implantology, and maxillofacial surgery. Extensive analysis explores the leading platforms in 3D printing such as stereolithography (SLA), fused deposition modeling (FDM), selective laser sintering (SLS), digital light processing (DLP), and PolyJet which all achieve superior performance across multiple areas including resolution capabilities, material compatibility options, clinical application readiness, and cost-effectiveness. Additionally, an extensive overview of common materials, including biocompatible polymers (PLA, PMMA, PEEK), metals (titanium, cobalt-chromium), and ceramics (zirconia, alumina, glass-ceramics), sheds light on the critical role of material selection for patient safety, durability, and functional performance. The review explores new advancements such as 4D printing with shape-adaptive smart biomaterials as well as artificial intelligence-enabled digital processes and prosthesis design for the transformation of regenerative dentistry and intraoral drug delivery operations into new domains and the automation of clinical planning. Equally groundbreaking are 3D printing applications in pediatric dentistry, surgical simulation, and dental education. However, full-scale adoption of AM technology is not without challenges, including material toxicity, regulatory hurdles for approval, high initial investments, and the need for extensive digital expertise training. Sustainability concerns are also being addressed, with recycled materials and circular economy models gaining traction. In conclusion, this article advocates for a future where dentistry is shaped by interdisciplinary collaboration, intelligent automation, and hyper-personalized biocompatible solutions, with 3D printing firmly established as the backbone of next-generation dental care. Full article

BJ3DP has unique advantages compared to other energy-beam-based additive manufacturing technologies, such as lower residual stress, arising from the lack of heat during the printing process and the uniformity of the sintering process. However, attaining both high density and dimensional precision in metallic materials remains a challenge in BJ3DP. This study presents a systematic investigation into the fabrication of high-melting-point pure chromium (Cr) via binder jetting 3D printing (BJ3DP), with a focus on optimizing the printing parameters and sintering conditions. An orthogonal experiment identified the optimal printing parameters as a layer thickness of 75 μm and a binder saturation of 60%, which resulted in green parts with a relative density of 57.1%—a representative value for BJ3DP processes that demonstrates effective parameter optimization. Subsequently, the green parts were sintered at 1800 °C for 9 h, resulting in a maximum density of 97.35%. The hardness of the as-sintered BJ3DP Cr parts was superior to that of samples produced by conventional levitation melting (184.20 HV vs. 171.20 HV). This work demonstrates that the no-heat printing strategy of BJ3DP effectively mitigates issues related to residual stress and cracking, providing a viable method for producing high-melting-point metallic materials. Full article

Additive manufacturing (AM) of hot-work tool steels such as H13 offers unique opportunities for producing complex, conformally cooled tools with reduced production time and material waste. In this study, five metal AM technologies—Fused Deposition Modeling and Sintering (FDMS, Desktop Metal Studio System and Zetamix), Binder Jetting (BJ), Laser Powder Bed Fusion (LPBF), and Directed Energy Deposition (DED)—were compared in terms of microstructure, porosity, and post-processing heat treatment response. The as-printed microstructures revealed distinct differences among the technologies: FDMS and BJ exhibited high porosity (6–9%), whereas LPBF and DED achieved near-full densification (<0.1%). Samples with sufficiently low porosity (BJ, LPBF, DED) were subjected to tempering and quenching treatments to evaluate hardness evolution and microstructural transformations. The satisfactory post-treatment hardness was observed in both tempered and quenched and tempered BJ samples, associated with secondary carbide precipitation, while LPBF and DED samples retained stable martensitic structures with hardness around 600 HV0.5. Microstructural analyses confirmed the dependence of phase morphology and carbide distribution on the thermal history intrinsic to each AM process. The study demonstrates that while FDMS and BJ are more accessible and cost-effective for low-density prototypes, LPBF and DED offer superior density and mechanical integrity suitable for functional tooling applications. Full article

Additive manufacturing (AM) technologies based on sintering, such as Powder Bed Fusion (PBF), Direct Energy Deposition (DED), Binder Jetting (BJT), and Material Extrusion (MEX), enable the production of complex metallic components with reduced material waste and design flexibility. However, the intrinsic porosity, microstructural anisotropy, and mechanical properties of sintered AM metals significantly influence their machinability, affecting tool wear, surface integrity, and cutting forces. This review explores the key material characteristics affecting the machining performance of sintered AM metals, focusing on conventional processes such as turning, milling, and drilling. The impact of microstructure, density, and mechanical properties on machining outcomes is analyzed, along with the challenges posed by the unique properties of sintered materials. Additionally, post-processing strategies, including heat treatments and surface finishing techniques, are discussed as potential solutions to enhance machinability. The review concludes by identifying future research opportunities, particularly in optimizing AM process parameters and developing hybrid manufacturing approaches to improve the industrial applicability of sintered AM metallic materials. Although previous studies focus on individual AM technologies, this review takes a novel approach by systematically comparing the machinability of metallic materials produced via PBF, DED, BJT, and MEX. By identifying commonalities and differences among these sintering-based AM processes, this work provides a comprehensive perspective on their machining behavior and post-processing requirements, offering valuable insights for industrial applications. Full article

This paper addresses ballistic protection, which is an important element in the performance of any military equipment. Improving ballistic properties is a necessity for individual protection through the use of protective vests. In this study, plasma jet thermal deposition was performed on ballistic protection materials, steel plates from the ARMOX category, using both metallic and ceramic powders. The samples with appropriate dimensions, covered with these types of powders, were analyzed from a microstructural point of view to determine their mechanical properties and evaluate the improvement in ballistic protection level. Microstructural analyses by optical and electronic microscopy, SEM (Scanning Electron Microscopy), allowed the performance of complex analyses regarding the adhesion of the deposits to the base material. It was possible to evaluate the microstructure, thickness, uniformity, and porosity of the deposits and the microstructural aspects at the interface between the base material and the deposit. For the efficient use of these deposits, tribological studies were carried out on the mechanical properties through scratch and microindentation analyses. The paper concludes the results obtained for the two types of deposits, metallic and ceramic, to streamline their use to increase the ballistic protection of bulletproof vests used in individual protection in military equipment. Full article

Metal binder jetting (MBJ) is an additive manufacturing technology of increasing interest due to its potential competitiveness in medium- and large-scale production, especially from a sustainability perspective. However, challenges in controlling the product accuracy and precision significantly limit the widespread adoption of this technology. This work investigates the achievable accuracy, precision, and spatial repeatability of parts produced using the MBJ process. Additionally, the paper aims to identify the causes of inaccuracy and suggest countermeasures to improve the product quality. The study was conducted experimentally by designing a benchmark geometry with various basic features. This geometry was scaled to three sizes—10–20 mm (small), 20–30 mm (intermediate), and 30–50 mm (large)—and produced using two different stainless-steel powders: AISI 316L and 17-4PH. In the green state, the dimensional tolerances ranged from IT8 to IT12 for features parallel to the build direction (heights) and from IT9 to IT13 for features parallel to the build plane (lengths). In the sintered state, the tolerances ranged from IT10 to IT16. This study reveals the challenges in scaling geometries to compensate for accuracy loss originating from the printing and sintering stages. In the green state, accuracy issues are likely due to non-uniform binder application and drying operations. In the sintered state, the accuracy loss is related to variable shrinkage based on the feature size, anisotropic shrinkage depending on the print direction, and differing densification mechanisms influenced by the material type. This study offers novel insights for improving MBJ process precision, supporting wider adoption in the manufacturing industry. Full article

This review presents recent advancements in cold atmospheric pressure (AP) plasma (CAP) processes for the synthesis and surface treatment of polymer films and metal nanoparticles (NPs) in biomedical applications. We discuss the properties and applications of atmospheric pressure plasma (APP) processes, including dielectric barrier discharge (DBD) and plasma jet methods, highlighting their effectiveness in controlling surface characteristics such as wettability and functionalization. Full article

Abrasive air jet machining is a burgeoning non-traditional machining technology particularly suitable for machining brittle non-metallic materials and metals with high hardness. It is very challenging to select the optimal process parameters to achieve desirable machining performance metrics, such as maximizing material removal rate and minimizing machining width while controlling machining depth. In this study, we aimed to achieve multi-objective process parameter optimization for abrasive air jet machining of silicon based on the artificial bee colony algorithm. A series of experiments was carried out to investigate the effect of process parameters, including air pressure, standoff distance, and nozzle traverse speed, on material removal rate, machining width, and machining depth. Mathematical models for machining performance metrics were developed by regression analysis, and a multi-objective optimization model was further formulated. The artificial bee colony algorithm was proposed to solve the optimization problem, and a set of Pareto-optimal solutions was found. The results indicate that the artificial bee colony algorithm is an effective method for multi-objective process parameter optimization in abrasive air jet machining. Full article

Due to its unique benefits over conventional subtractive manufacturing, additive manufacturing methods continue to attract interest in both academia and industry. One such method is called Cold Spray Additive Manufacturing (CSAM), a solid-state coating deposition technology to manufacture repair metallic components using a gas jet and powder particles. CSAM offers low heat input, stable phases, suitability for heat-sensitive substrates, and high deposition rates. However, persistent challenges include porosity control, geometric accuracy near edges and concavities, anisotropy, and cost sensitivities linked to gas selection and nozzle wear. Interdisciplinary research across manufacturing science, materials characterisation, robotics, control, artificial intelligence (AI), and machine learning (ML) is deployed to overcome these issues. ML supports quality prediction, inverse parameter design, in situ monitoring, and surrogate models that couple process physics with data. To demonstrate the impact of AI and ML on CSAM, this study presents a systematic literature review to identify, evaluate, and analyse published studies in this domain. The most relevant studies in the literature are analysed using keyword co-occurrence and clustering. Four themes were identified: design for CSAM, material analytics, real-time monitoring and defect analytics, and deposition and AI-enabled optimisation. Based on this synthesis, core challenges are identified as small and varied datasets, transfer and identifiability limits, and fragmented sensing. Main opportunities are outlined as physics-based surrogates, active learning, uncertainty-aware inversion, and cloud-edge control for reliable and adaptable ML use in CSAM. By systematically mapping the current landscape, this work provides a critical roadmap for researchers to target the most significant challenges and opportunities in applying AI/ML to industrialise CSAM. Full article

To address the greenhouse effect and environmental pollution stemming from fossil fuels, the development of new energy sources is widely regarded as a critical pathway toward achieving carbon neutrality. Microalgae, as a feedstock for third-generation biofuels, have emerged as a research hotspot for producing biojet fuel due to their high photosynthetic efficiency, non-competition with food crops, and potential for carbon reduction. This paper provides a systematic review of technological advancements in the catalytic hydrogenation of microalgal oil for biojet fuel production. It specifically focuses on the reaction mechanisms and catalyst design involved in the hydrogenation–deoxygenation and cracking/isomerization processes within the Oil-to-Jet (OTJ) pathway. Furthermore, the paper compares the performance differences among various catalyst support materials and between precious and non-precious metal catalysts. Finally, it outlines the current landscape of policy support and progress in industrialization projects globally. Full article