Search Results (3,153)

The linear economic model continues to drive multidimensional environmental problems, as it generates large volumes of plastic waste, as well as agricultural by-products, such as coconut husks. On the other hand, the maritime industry still relies on conventional materials such as wood, steel, and fibre-reinforced plastics, which have several usage challenges, including corrosion, toxicity, and difficulties associated with end-of-life management. These issues point to the need for more sustainable material options. This review examines the potential of combining coconut fibre (coir) with recycled plastics to produce a functional material for use in the maritime sector. The material is designed to add value to waste streams by providing a practical approach to reducing dependence on conventional and less sustainable resources. The review discusses fibre treatments (alkali, silane, acetylation) and fabrication methods (compression moulding, extrusion) and evaluates their impact on mechanical performance and durability. The studies show that coir–plastic composites possess highly tuneable mechanical properties. Tensile strengths are reported to range from approximately 2.4 MPa for natural resin matrices to 78 MPa for polyester hybrids, while the flexural modulus can be increased by up to 99% compared to the neat polymer blend. Fibre treatments (e.g., alkali) and fabrication methods are crucial, as they have been shown to improve tensile and flexural strength by over 40% and impact strength by 150%. However, the composites produced still show vulnerability to water absorption, UV radiation, and biofouling, which could limit their application in marine environments. To this end, several issues require further study, including long-term field validation, enhanced understanding of material fatigue, and scalable manufacturing. Full article

The increasing demand for porous stainless-steel materials produced by selective laser melting (L-PBF) for biomedical implants, filtration systems, heat exchangers, and energy devices has created an urgent need to improve their mechanical performance. Optimizing process parameters and microstructural properties is therefore critical for enhancing the overall functionality and reliability of L-PBF porous stainless-steel structures. This paper studies the effect of an aging heat treatment on the mechanical properties of L-PBF specimens, manufactured with stainless steel Uddeholm Corrax powders. The porosity was selected to be about 3%, based on manufacturer’s experience on the production injection mold inserts, with the ability to drain air. To reach this porosity, a set of manufacturing variables were selected, quantified in terms of VED (Volumetric Energy Density) of 59.01 J/mm³. The analysis of the mechanical behavior was focused on the compressive and flexural strength, dynamic Young’s modulus and the energy dissipation during earlier fatigue loading cycles. This study concluded that the heat treatment produces a negligible effect on dynamic Young’s modulus and increases the bending strength by about 25% and the compressive plateau strength by about 17%. Both specimens’ batches exhibit similar fatigue strain accumulation for cyclic compressive tests. Full article

Digital twins enable closed-loop process control in smart manufacturing, yet no quantitative mapping exists between controller computational complexity and achievable real-time performance class. This paper aims to establish a quantitative mapping between controller computational complexity and achievable real-time performance class in digital twin-based process control, providing evidence-based deployment guidance for smart manufacturing. Three controller architectures—proportional–integral–derivative, model predictive control, and its robust variant—are implemented and timed on a finite-difference state-space model of a 1 mm steel slab under boundary heat flux, representative of laser-based and induction heating in manufacturing. Per-cycle latency is characterized through time series, cumulative distribution analysis, and deadline-miss rate on standard hardware without real-time operating system support. The proportional–integral–derivative controller satisfies hard real-time constraints with sub-0.05 ms latency; model predictive control with warm-starting achieves a 99th-percentile latency of 2.43 ms against a 10 ms deadline with zero misses across all tested prediction horizons. Robust model predictive control yields a mean latency of 770 ms—154 times the 5 ms control period—placing it firmly in the near-real-time class. A robust linear matrix inequality delay-margin analysis certifies closed-loop stability bounds across three uncertainty scenarios as a function of actuation delay; a finite-horizon induced-gain metric reveals a worst-case disturbance amplification peak near 100 control steps. Model predictive control is shown to compensate for actuation delays up to 50 ms that destabilize proportional–integral control, establishing it as the preferred architecture in latency-constrained digital twin deployments. Full article

Wire Arc Additive Manufacturing (WAAM) has emerged as a cost-effective and high-deposition-rate technique for fabricating large-scale metallic components; however, the complex thermal history inherent to the process leads to heterogeneous microstructures that can significantly influence tribological performance. In this study, the dry sliding wear behavior of WAAM-fabricated austenitic stainless steel 308L (SS308L) was systematically investigated using a pin-on-disk configuration. The influence of applied normal load (1.5–15 N) and sliding speed (0.03–0.229 m/s) on wear volume, specific wear rate, coefficient of friction (COF), and tangential force was evaluated. Optical microstructural observations indicated features consistent with a ferritic–austenitic solidification structure, including regions resembling polygonal ferrite, Widmanstätten ferrite, and austenitic dendritic morphologies. Wear results showed that wear volume and cross-sectional area increased monotonically with increasing load, while the effect of sliding speed was comparatively less significant. The specific wear rate remained on the order of 10⁻⁴ mm³/N·m with minor variations across test conditions. The COF decreased with increasing load up to 10 N, followed by a speed-dependent response at higher loads. The findings demonstrate that load is the dominant factor governing wear behavior in WAAM SS308L, while microstructural heterogeneity may contribute to frictional stability and wear resistance. This study provides valuable insight into the structure–tribology relationship of WAAM stainless steels and supports the optimization of process parameters for wear-critical applications. Full article

The main aim of this study is to investigate the microstructure and microhardness of Wire Arc Additive Manufactured (WAAM) samples produced under different layer deposition strategies and corresponding interlayer temperature conditions. Experimental samples were produced using the WAAM process with X45CrSi9-3 steel. During the experiments, both the number of layers and the thermal conditions (heating and cooling) were systematically varied. This was achieved by fabricating samples consisting of five layers with three beads per layer. The layer deposition procedure was implemented in two different ways: (i) with a waiting period after each layer to allow cooling to room temperature, and (ii) without such a waiting period. Thermal cycles at selected locations within the samples were calculated using simulation modeling. By combining these thermal cycles with the continuous cooling transformation (CCT) diagram, the expected microstructures in the vicinity of these locations were determined. These predictions were supplemented by microstructural analysis and hardness measurements. Particular emphasis was placed on the influence of interlayer temperature and repeated heating and cooling cycles. The analyses enabled the identification of process parameters that facilitate control over microstructure, microhardness, and property gradients. It can be concluded that the interlayer holding time provides an effective means of controlling the microstructure of the workpiece, ranging from predominantly austenitic to predominantly martensitic. Depending on the thermal cycles, the measured microhardness varied within the range of 360–900 HV. Metallographic examination revealed a wide spectrum of non-equilibrium microstructures, including martensite with varying degrees of tempering, retained austenite, pearlite, and bainite. The application of a thermal model to the conducted experiments, combined with the CCT diagram, indicated that the expected microstructures consist predominantly of martensite with varying degrees of tempering, retained austenite, carbides, and, in some cases, up to 5% pearlite. Full article

This article presents a new combined post-processing concept to improve the quality of laser powder bed fusion (LPBF) of 17-4PH stainless steel (SS) cylindrical parts fabricated from N₂-atomised LaserForm 17-4PH (B) powder. The concept is based on consecutive heat treatment procedures and diamond burnishing (DB) processes. A two-stage study was conducted. The first stage was an LPBF process experiment. The following combination of LPBF parameter values was selected after optimisation: a laser power of $\mathrm{P}=150 \mathrm{W}$, laser scanning speed of v = 1200 mm/s, and layer thickness of $\mathrm{t}=40 \mathsf{\mu }\mathrm{m}$. In the second stage, this combination was used to evaluate the effects of two heat treatment procedures (HT1 and HT2) and two DB processes (using burnishing forces of 100 N and 300 N) on the tensile properties and surface integrity of LPBF 17-4PH SS cylindrical samples. The HT2 procedure, including annealing $({1200}^{\circ }$, $4 \mathrm{h})$, solution treatment (${1060}^{\circ }$, $1 \mathrm{h})$, cooling (${-70 }^{\circ }\mathrm{C},2 \mathrm{h}$), and ageing (${482}^{\circ }$, $4 \mathrm{h}$) led to yield limit, tensile strength, and Vickers hardness values of $\mathrm{Y}\mathrm{L}=1071 \mathrm{M}\mathrm{P}\mathrm{a}$, $\mathrm{T}\mathrm{S}=1410 \mathrm{M}\mathrm{P}\mathrm{a}$, and $523 \mathrm{H}\mathrm{V},$ respectively. The concept presented takes advantage of the combination of the transformation, precipitation and strain-hardening effects. The combined effect was most pronounced in the samples subjected to the HT2 procedure and subsequent DB (300 N), for which a retained austenite fraction of 6.93%, surface microhardness of ${563 \mathrm{H}\mathrm{V}}_{0.05}$ and the maximum values of the compressive axial and hoop RSs of $-1426.3 \mathrm{M}\mathrm{P}\mathrm{a}$ and $-1095.9 \mathrm{M}\mathrm{P}\mathrm{a}$, respectively, were measured. Full article

The unique powder-pack boriding technique using an open retort with boriding medium was applied for the first time in order to produce boride layers on K190 ledeburitic chromium steel manufactured using powder metallurgy. The processes were carried out using the commercial Durborid^®G powder mixture at 1173 K, 1223 K, and 1273 K for 3 h, 6 h, and 9 h. As a result of the boriding of the high-carbon and high-chromium substrate, three zones were revealed in the produced surface layers: the outer FeB zone, the inner Fe₂B zone, and the transition zone, with increased carbon content. The total thickness of the boride layers (FeB + Fe₂B) ranged from 14.13 µm at the lowest temperature and shortest time to 65.49 µm at the highest temperature and longest duration. Increasing the temperature and extending the boriding time resulted in a deeper FeB zone as well as a thicker total layer (FeB + Fe₂B). The growth kinetics of the produced layers on the surface of K190 steel were analyzed for the first time using the mean diffusion coefficient model. The thicknesses of the FeB zone and the total layer (FeB + Fe₂B) were determined. The activation energies of boron for the FeB and Fe₂B phases calculated in this work are comparable with other results for the powder-pack boriding of high-carbon tool steels. As a consequence of the high chromium content in K190 steel, chromium borides were observed in the boride zones, which increased the hardness of the surface layer. The highest temperature used resulted in the formation of vanadium borides. The presence of the transition zone with an increased carbon concentration and a high percentage of carbides resulted from the movement of carbon atoms toward the core by the advancing boron diffusion front. The parameters of boriding (temperature and time) as well as the presence of alloying elements in the substrate material influenced the microhardness of the boride layers. Full article

The increasing demand for sustainable and lightweight structural systems has motivated the development of alternative materials for wind turbine tower applications, where conventional steel structures are associated with high material consumption and environmental impact. In this study, a novel steel-reinforced recycled thermoplastic composite system is proposed as an alternative structural solution. To enable the design and practical application of such composite systems, the mechanical properties of the recycled thermoplastic matrix were experimentally characterized. Compression and tensile tests revealed average yield strengths of approximately 32 MPa in compression and 7.8 MPa in tension. To account for the environmental conditions encountered in field applications, the temperature-dependent mechanical behavior of the material was investigated. Since the critical mechanical response of the thermoplastic matrix in the composite system is governed by compression rather than tension, the study was limited to compression tests under elevated temperatures. The results show that the compressive yield strength decreases to approximately 31 MPa at 55 °C. An analytical model based on the transformed-section approach was also developed to predict the flexural behavior of the composite section and was validated through three-point bending tests, with an analytically predicted yield load of approximately 31.5 kN showing good agreement with experimental results. To assess structural applicability at a larger scale, a full-scale composite wind turbine tower was designed and manufactured, and its dynamic performance was evaluated through field measurements under natural wind loading conditions. The results indicate that the composite tower exhibits comparable dynamic behavior to a conventional steel tower, with a first natural frequency of approximately 3.08 Hz compared to 2.89 Hz for the steel tower, along with enhanced damping characteristics. These findings demonstrate that steel-reinforced recycled thermoplastic composites offer a promising and sustainable alternative for wind turbine tower applications, with potential for broader use in structural systems. Full article

In the manufacturing process of high-grade non-oriented electrical steel, cast billets are subjected to hot rolling and normalizing treatments. These processes are implemented to optimize the microstructure and texture of steel sheets during production, mitigate corrugated defects, and enhance the magnetic properties of the final finished sheets. In this study, two types of high-strength non-oriented silicon steel test specimens were prepared via the incorporation of the trace alloying element Sn, namely one without Sn addition and the other with 0.045 wt% Sn. The test specimens were first hot-rolled to a thickness of 2.0 mm, followed by normalization treatment in the laboratory to simulate the continuous normalizing process employed by a domestic steel mill. The effects of Sn on the normalized microstructure, texture, and precipitates of non-oriented silicon steel tailored for new energy vehicles were investigated. The findings reveal that the alloying element Sn can increase the thickness of the recrystallized layer on the surface of hot-rolled sheets and refine the grain size of non-oriented silicon steel. After continuous normalizing treatment, a comparison between the two test specimens shows that as the normalizing temperature rises, the reduction in average grain size of the 0.045 wt% Sn specimen relative to the Sn-free specimen increases from 1.4% to 15.96%. Additionally, the incorporation of Sn reduces the fraction of the {111} texture component (detrimental to magnetic properties) while increasing the fraction of the {100} texture component (beneficial to magnetic properties) in the non-oriented silicon steel. Precipitates exhibited significant coarsening and a reduction in number with increasing temperature, while the addition of Sn exerted a certain inhibitory effect on precipitate growth. Furthermore, the 0.045 wt% Sn-containing test specimen achieved an optimal balance between magnetic and mechanical properties when subjected to normalization at 980 °C and annealing at 920 °C. Under these processing conditions, the magnetic induction B₅₀ reached 1.733 T, the iron loss P_1.5/50 was 2.01 W/kg, the yield strength was 410 MPa, and the tensile strength was 529 MPa. Full article

Wire Arc Additive Manufacturing (WAAM) is a cost-effective and scalable technique for producing large metallic components; however, coarse columnar microstructures, strong crystallographic texture, and significant residual stresses limit its widespread adoption. Hybrid WAAM processes that integrate deformation-based techniques have been developed to address these limitations. This review provides an analysis of deformation-assisted WAAM, covering interlayer rolling, friction stir processing (FSP), machine hammer peening, laser shock peening, and ultrasonic-vibration-assisted techniques. These hybrid techniques introduce additional thermomechanical parameters (strain, strain rate, and applied stress) that significantly influence microstructure evolution. The governing physical metallurgy mechanisms are discussed in detail, including dislocation accumulation, recovery, static and dynamic recrystallization, and severe plastic deformation. Studies from 2022 to 2025 are critically reviewed, highlighting the effectiveness of hybrid WAAM in promoting columnar-to-equiaxed grain transformation, reducing anisotropy, mitigating defects, and improving mechanical properties across aluminum, titanium, steels, and nickel-based alloys. The integration of auxiliary processes such as in situ machining and heat treatment is also discussed. This review establishes a process–structure–property framework for hybrid WAAM and provides guidance for the development of advanced additive manufacturing systems for the production of near-net-shape components, with reported yield-strength gains of 20–40%, elongation gains of 10–30%, and fatigue-life improvements of up to 60% relative to as-built WAAM. Full article

Additive manufacturing through a laser cladding has been shown to be an effective technology for the mitigation of wear and rolling contact fatigue (RCF) of railway track. Small-scale tests have consistently shown that creating a thin layer of premium material on the tribo-active surface of the railhead vastly reduces wear and suppresses the onset of RCF due to the ratcheting mechanism being almost eliminated in comparison to standard rail material. Cladding reduces material plastic flow by 60% which is a cause of insulated track joint failure. This paper reports results from the first full-scale trials of additively manufactured laser clad layers on railway rails by studying their mechanical properties and microstructure. This is a vital step in safely progressing this technology from lab scale to network application. Tested full-scale insulated block joint (IBJ) specimens, clad with martensitic stainless steel (MSS) and Stellite 6, were sectioned, polished and etched and the microstructures of the clad, heat-affected zone and parent rail materials were inspected using optical and scanning electron microscopy (SEM) (Hitachi TM3030 plus, Tokyo, Japan). Residual stress was also measured. Cladding with MSS and Stellite 6 showed high wear and RCF resistance after the tests. Material flow was reduced with the clad layer applied. No defects such as porosity or large precipitates were observed in the heat-affected zone (HAZ), particularly close to the rail surface at the clad end which could act as a point of weakness. Residual stress states varied between materials, MSS being compressive (−344 MPa average) and Stellite 6 being tensile (+391 MPa average) which could have an impact on the fatigue life of the clad. This finding matches previous work, indicating that MSS may be preferable in the field, where bending of rails can occur. Overall, the work showed that laser cladding can provide a good solution to lipping issues and wear problems of rail in IBJs. Analysis in this work confirmed that the HAZ where clad meets the bulk rail at the surface has good structural integrity; however, this needs to be a focus of attention in field application of these layers. Full article

Background and Objectives: Conventional stainless-steel orthodontic molar bands may exhibit limited anatomical adaptation, favoring plaque retention and periodontal inflammation. This study aimed to compare the periodontal outcomes of standard bands and CAD/CAM-customized molar bands in adolescents. Materials and Methods: A prospective randomized controlled clinical study was conducted in 180 adolescents (mean age: 11.9 years) undergoing fixed orthodontic therapy. Participants were allocated to CAD/CAM-customized bands (n = 90) or standard stainless-steel bands (n = 90). Periodontal parameters—Plaque Control Record (PCR), Bleeding on Probing (BOP), and Periodontal Probing Depth (PPD)—were assessed at baseline, 1, 3, and 6 months. Data were analyzed using the Mann–Whitney U test (p < 0.05). Results: Baseline values were comparable between groups (p > 0.05). During follow-up, the CAD/CAM group showed significantly lower PCR, BOP, and PPD values. At 6 months, PCR was 21 ± 8% vs. 42 ± 12%, BOP was 17 ± 6% vs. 40 ± 10%, and PPD was 2.5 ± 0.5 mm vs. 3.1 ± 0.6 mm (all p < 0.001). Conclusions: CAD/CAM-customized molar bands demonstrated superior periodontal performance compared with conventional bands. Improved anatomical adaptation may reduce plaque accumulation and gingival inflammation during orthodontic treatment. Full article

This study investigates the influence of specific heat input and weld configuration on heat affected zone hardness and residual stress of S960MC high strength steel welds. In total, five types of weld samples were manufactured by Tungsten Inert Gas (TIG) autogenous welding and Metal Active Gas (MAG) butt welding to simulate the effect of increasing heat input and constraining the relative motion of welded parts during the heating and cooling phase. The obtained results show that the highest axial tensile residual stresses with magnitude above 900 MPa, combined with a hardness drop in a range from 13 up to 18%, occur mostly in the sub-critical heat affected zone, making it the critical zone of the weld. Increasing the heat input during welding does not have a simple correlation with generating more residual stresses and the trends obtained on the surface are different from results evaluated at a depth of 0.2 mm. Restraining the relative part motion during the welding affects mostly the tangential residual stresses, causing an increase in their tensile magnitude localized in the middle of the heat-affected zone while almost no influence on the axial residual stress component was recorded. Full article

The demand for high-nitrogen austenitic stainless steel (HNASS) powders has become increasingly urgent due to the rapid development of advanced manufacturing processes. However, it still remains a challenge to accurately control the nitrogen content and its chemical state. In this work, an innovative process combining high-pressure metallurgy and solid-state powder nitriding is proposed to prepare ultra-high nitrogen austenitic stainless steel powders. The prepared powders not only exhibit fine austenite grains, but also achieve a high nitrogen content of up to 5.63 wt.% at 1000 °C, 2.5 h, and 2.5 MPa. The results demonstrate that the phase composition of the powders, as well as the size and distribution of nitrides can be effectively regulated by carefully controlling the key processing parameters including temperature, time and pressure. Nitrogen is predominantly uniformly distributed as solid solution, with minor nanoscale nitride precipitates. XPS analysis of the powder surface indicates that the peak area ratios of N1s (N 1s core-level) in the form of solid solution and nitrides are ~82.95% and ~17.05%, respectively. And the peak area ratios of N1s at different depths of the powder do not show significant changes. Furthermore, the high-pressure nitriding mechanism reveals that the synergy between a high-pressure nitrogen atmosphere and solid-state nitriding enhances nitrogen diffusion flux and increases nitride nucleation density, enabling precise control of nitrogen content and precipitate size. Moreover, the high-pressure nitriding process can effectively keep nitrogen in a solid solution, prevent the precipitation of coarse nitrides, and consequently improve the quality of the powders. This research provides in-depth guidance and insights into the design and preparation of HNASS powders. Full article