Search Results (822)

The authors of this paper investigated the process parameters of high-speed laser cladding of TC4/AISI431 composite coatings on the surface of C45 steel, choosing laser power, scanning speed, and TC4 addition as the experimental factors, and porosity, microhardness, and corrosion resistance as the target indices. A regression model was established based on the response surface methodology BBD, and the reliability of the model was analyzed using an ANOVA. Then, the WOA was used for multi-objective optimization. The optimal parameter set was determined as follows: a laser power of 5315 W, a scanning speed of 378 mm/s, and a TC4 addition of 3.6%. The microstructure and surface elemental composition of the coating were analyzed. The results showed that the porosity reduced by 60% and that the corrosion resistance improved by 79.98%, while the microhardness remained essentially unchanged. Full article

This study aims to enhance the performance of an innovative steel slag–ceramsite foam concrete (SSCFC) to advance sustainable green building materials. An eco-friendly composite construction material was developed by integrating industrial by-product steel slag (SS) with lightweight ceramsite. Employing a three-factor, three-level orthogonal experimental design at a fixed density of 800 kg/m³, 12 mix proportions (including a control group) were investigated with the variables of water-to-cement (W/C) ratio, steel slag replacement ratio, and ceramsite replacement ratio. The governing mechanisms of the W/C ratio, steel slag replacement level, and ceramsite replacement proportion on the SSCFC’s fluidity and compressive strength (CS) were elucidated. The synergistic application of range analysis and analysis of variance (ANOVA) quantified the significance of factors on target properties, and partial least squares regression (PLSR)-based prediction models were established. The test results indicated the following significance hierarchy: steel slag replacement > W/C ratio > ceramsite replacement for fluidity. In contrast, W/C ratio > ceramsite replacement > steel slag replacement governed the compressive strength. Verification showed R² values exceeding 65% for both fluidity and CS predictions versus experimental data, confirming model reliability. Multi-criteria optimization yielded optimal compressive performance and suitable fluidity at a W/C ratio of 0.4, 10% steel slag replacement, and 25% ceramsite replacement. Full article

Accurate melt pool geometry prediction is essential for ensuring quality and reliability in Laser Powder Bed Fusion (L-PBF). However, small experimental datasets and limited physical interpretability often restrict the effectiveness of traditional machine learning (ML) models. This study proposes a hybrid framework that integrates an explicit thermal model with ML algorithms to improve prediction under sparse data conditions. The explicit model—calibrated for variable penetration depth and absorptivity—generates synthetic melt pool data, augmenting 36 experimental samples across conduction, transition, and keyhole regimes for 316 L stainless steel. Three ML methods—Multilayer Perceptron (MLP), Random Forest, and XGBoost—are trained using fivefold cross-validation. The hybrid approach significantly improves prediction accuracy, especially in unstable transition regions (D/W ≈ 0.5–1.2), where morphological fluctuations hinder experimental sampling. The best-performing model (MLP) achieves R² > 0.98, with notable reductions in MAE and RMSE. The results highlight the benefit of incorporating physically consistent, nonlinearly distributed synthetic data to enhance generalization and robustness. This physics-augmented learning strategy not only demonstrates scientific novelty by integrating mechanistic modeling into data-driven learning, but also provides a scalable solution for intelligent process optimization, in situ monitoring, and digital twin development in metal additive manufacturing. Full article

This article provides a comprehensive overview of recent studies concerning laser heat treatment (LHT) of structural and tool steels, with particular attention to the 21NiCrMo2 steel used for carburized gear wheels. Analysis includes the influence of critical laser processing conditions—including power output, motion speed, spot size, and focusing distance—on surface microhardness, hardening depth, and microstructure development. The findings indicate that the energy density is the dominant factor that affects the outcomes of LHT. Optimal results, in the form of a high surface microhardness and a sufficient depth of hardening, were achieved within the energy density range of 80–130 J/mm², allowing for martensitic transformation while avoiding defects such as melting or cracking. At densities below 50 J/mm², incomplete hardening occurred with minimal microhardness improvement. On the contrary, densities exceeding 150–180 J/mm² caused surface overheating and degradation. For carburized 21NiCrMo2 steel, the most effective parameters included 450–1050 W laser power, 1.7–2.5 mm/s scanning speed, and 2.0–2.3 mm beam diameter. The review confirms that process control through energy-based parameters allows for reliable prediction and optimization of LHT for industrial applications, particularly in components exposed to cyclic loads. Full article

Laser powder bed fusion (LPBF) is an advanced additive manufacturing technology that is gaining increasing interest for biomedical implants because it can produce dense, patient-specific metallic components with controlled microstructures. This study investigated the LPBF fabrication of 316L stainless steel, which is widely used in orthopedic and dental implants, and examined the effects of laser power and scanning speed on the microstructure and mechanical properties relevant to biomedical applications. The study achieved 99.97% density and refined columnar and cellular austenitic grains, with optimized molten pool morphology. The optimal LPBF parameters, 190 W laser power and 700 mm/s, produced a tensile strength of 762.83 MPa and hardness of 253.07 HV_0.2, which exceeded the values of conventional cast 316L stainless steel. These results demonstrated the potential of optimized LPBF 316L stainless steel for functional biomedical applications that require high mechanical integrity and biocompatibility. Full article

Laser beam powder bed fusion of metals (PBF-LB/M, or simply L-PBF) has emerged as one of the most competitive additive manufacturing technologies for producing complex metallic components with high precision, design freedom, and minimal material waste. Among the various categories of additive manufacturing processes, L-PBF stands out, paving the way for the execution of part designs with geometries previously considered unfeasible. Despite offering several advantages, parts with overhang features require the use of support structures to provide dimensional stability of the part. Support structures achieve this by resisting residual stresses generated during processing and assisting heat dissipation. Although the scientific community acknowledges the role of support structures in the success of L-PBF manufacturing, they have remained relatively underexplored in the literature. In this context, the present work investigated the impact of laser power and scanning speed on the dimensioning, integrity and tensile strength of single-walled block type support structures manufactured in AISI 316L stainless steel. The method proposed in this work is divided in two stages: processing parameter exploration, and mechanical characterization. The results indicated that support structures become more robust and resistant as laser power increases, and the opposite effect is observed with an increment in scanning speed. In addition, defects were detected at the interfaces between the bulk and support regions, which were crucial for the failure of the tensile test specimens. For a layer thickness corresponding to 0.060 mm, it was verified that the combination of laser power and scanning speed of 150 W and 500 mm/s resulted in the highest tensile resistance while respecting the dimensional deviation requirement. Full article

The central role of heating and cooling in energy transition has been recognised in recent years, especially with geopolitical developments since February 2022 which demand an acceleration in deploying local energy sources to increase the resilience of the energy sector. Geothermal energy is a promising and vital option to optimize heating and cooling systems, promoting sustainability of urban environments. To this end, a proper design is of paramount importance to guarantee the energy performance of the whole system. This work deals with the optimization of the technical and geometrical characteristics of borehole heat exchangers (BHEs) as part of a shallow geothermal plant that is assumed to be integrated in an already operating gas-fired DH grid. Thermal performances of three different configurations were analysed according to the geological information that revealed an aquifer at −36 m overlying a poorly permeable marly succession. Numerical simulations validated the geological, hydrogeological, and thermo-physical models by back-analysing the experimental results of a thermal response test (TRT) on a pilot 150 m deep BHE. Five-year simulations were then performed to compare 150 m and 36 m polyethylene 2U, and 36 m steel coaxial BHEs. The coaxial configuration shows the best performance both in terms of specific power (74.51 W/m) and borehole thermal resistance (0.02 mK/W). Outcomes of the study confirm that coupling the best geological and technical parameters ensure the best energy performance and economic sustainability. Full article

An analysis of the working surfaces of cylindrical gears after scuffing shock tests allowed for the assessment of the effect of loading conditions on the form of damage to the tooth surfaces. Unlike the method of scuffing under severe conditions, where loading is applied gradually, the presented tests employed direct maximum loading—shock loading—without prior lapping of the gears under lower loads. This loading method significantly increases the vulnerability of the analyzed components to scuffing, enabling an evaluation of their limit in terms of operational properties. To identify the changes and the types of the teeth’s working surface damage, the following microscopy techniques were applied: scanning electron microscopy (FE-SEM) with EDS microanalyzer, optical interferential profilometry (WLI), atomic force microscope (AFM), and optical microscopy. The results allowed us to define the characteristic damage mechanisms and assess the efficiency of the applied DLC coatings when it comes to resistance to scuffing in shock scuffing conditions. Tribological tests were performed by means of an FZG T-12U gear test rig in a power circulating system to test cylindrical gear scuffing. The gears were made from 18CrNiMo7-6 steel and 35CrMnSiA nano-bainitic steel and coated with W-DLC/CrN. Full article

Plow loosening machines are essential agricultural machinery in the agricultural production process. Improving the surface strengthening process and extending the working life of the plow teeth of the plow loosening machine are of great significance. In this paper, the preparation of Stellite6/Cu composite coating on the surface of 316L steel substrate intended for strengthening the plow teeth of a plow loosening machine using laser cladding technology was studied. The influence of different laser process parameters on the microstructure and properties of Stellite6/Cu composite coating was investigated. The composite coating powder was composed of Stellite6 powder with a different weight percent of copper. Microstructural analysis, phase composition, elemental distribution, microhardness, wear resistance, and corrosion resistance of the composite coatings on the plow teeth were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness testing, energy dispersive spectroscopy (EDS), friction and wear testing, and electrochemical workstation measurements. The results showed that (1) When the laser power was 1000 W, the average hardness of the prepared Stellite6/Cu composite layer achieved the highest hardness, approximately 1.36 times higher than the average hardness of the substrate, and the composite coating prepared exhibited the best wear resistance; (2) When the scanning speed was 800 mm/min, the composite coating exhibited the lowest average friction coefficient and the optimal corrosion resistance in a 3.5% wt.% NaCl solution with a self-corrosion current density of −7.55 µA/cm²; (3) When the copper content was 1 wt.%, the composite coating achieved the highest average hardness with 515.2 HV, the lowest average friction coefficient with 0.424, and the best corrosion resistance with a current density of −8.878 µA/cm². Full article

Eco-friendly mortars have been manufactured with hybrid binders made of blast furnace slag and a reduced amount of clinker. The objective is to explore new formulations suitable for reinforced structures. Previous studies are mainly focused on activation with sulfates, a salt that is corrosive to reinforcing steel. Sodium nitrate and sodium carbonate, easily implementable in construction, have been used as activators in two different concentrations that involve similar Na content. A Type II PC mortar is used as reference. The dimensional stability of the mortars during curing (at 99% RH) and subsequent drying at 40% RH, has been evaluated, as well as their porosity and mechanical properties. Böhme tests revealed that studied hybrid binders have lower wear resistance than PC mortar. Activation with Na₂CO₃ allows the obtention of mortars with reduced porosity and good compression resistance, but generates microcracking that favors chloride diffusion. Activation with nitrates favors precipitation of AFm phases identified through differential thermal analysis. Nitrates in moderate amounts (4% w/w) allow manufacturing hybrid mortars with good resistance to chloride penetration and reasonably good mechanical properties. Hence, this binder can be a promising option for reinforced structures. Higher amounts of nitrates (8%) for activation give rise to more porous mortars. Full article

Approximately 20% of emissions from air travel are attributed to the auxiliary power units (APUs) carried in commercial aircraft. This paper proposes to reduce greenhouse gas emissions in international air transport by adopting proton-exchange membrane (PEM) fuel cells to replace APUs in commercial aircraft: we consider the design of three compressed hydrogen storage vessels made of 304 stainless steel, 6061-T6 aluminium, and Grade 5 (Ti-6Al-4V) titanium and capable of delivering 440 kW—enough for a PEM fuel cell for a Boeing 777. Complete structural analyses for pressures from 35 MPa to 70 MPa and wall thicknesses of 25, 50, 100, and 150 mm are used to determine the optimal material for aviation applications. Key factors such as deformation, safety factors, and Von Mises equivalent stress are evaluated to ensure structural integrity under a range of operating conditions. In addition, CO₂ emissions from a conventional 440 kW gas turbine APU and an equivalent PEM fuel cell are compared. This study provides insights into optimal material selection for compressed hydrogen storage vessels, emphasising safety, reliability, cost, and weight reduction. Ultimately, this research aims to facilitate the adoption of fuel cell technology in aviation, contributing to greenhouse emissions reduction and hence sustainable air transport. Full article

Recycling plastics waste into concrete represents one of the possible approaches for its valorization, offering both economic and environmental benefits. Although numerous studies have explored the mechanical properties of concrete with plastics waste, its durability performance remains largely unexplored. In this context, this study aims to assess the electrochemical behavior of rebars embedded in reinforced concrete modified by partially replacing natural aggregates with recycled plastics, comparing their behavior to that of conventional concrete. The corrosion of reinforcing steel bars was evaluated by wet and dry cycles (w/d) in calcium chloride solutions, monitoring corrosion potential and potentiostatic polarization resistance, and recording electrochemical impedance spectroscopy (EIS) and polarization curves. In addition, the chloride diffusion tendency and the mechanical performances were assessed in unreinforced samples. The findings indicate that in environments with lower chloride concentrations, concrete with plastic granules provides good protection against rebar corrosion. Although the mechanical results of the studied mixes confirmed that incorporating plastic granules as aggregates in the concrete matrix causes a reduction in compressive strength, as known in the literature, the modified concrete also exhibits improved post-cracking behavior, resulting in enhanced ductility and fracture toughness. Full article

The unique structures and properties of natural organisms provide abundant inspiration for surface modification research in materials science. In this paper, the tribological advantages of radial ribs found on shell surfaces were combined with laser cladding to address challenges in material surface strengthening. Laser cladding technology was used to fabricate bionic units on the surface of 20CrMnTi steel. The alloy powder consisted of a Ni-based alloy with added WC particles. The influence of laser power (1.0 kW–3.0 kW) on the dimensions, microstructure, hardness, surface roughness, and tribological properties of the bionic units was investigated to enhance the tribological performance of the Ni60/WC bionic unit. The microstructure, phase composition, hardness, and tribological behavior of the bionic units were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), a microhardness tester, and a wear tester. Experimental results show that the dimensions of the bionic units increased with laser power. However, beyond a certain threshold, the growth rate of the width and height gradually slowed due to heat conduction and edge cooling effects. The microstructure primarily consisted of equiaxed and dendritic crystals, with grain refinement observed at higher laser powers. The addition of WC resulted in average hardness values of 791 HV_0.2, 819 HV_0.2, 835 HV_0.2, and 848 HV_0.2 across the samples. This enhancement in hardness was attributed to dispersion strengthening and grain refinement. Increasing the laser power also reduced the surface roughness of the bionic units, though excessively high laser power led to a roughness increase. The presence of WC altered the wear mechanism of the bionic units. Compared to the wear observed in the N60 sample, the wear amount of the WC-containing samples decreased by 73.7%, 142.1%, 157.5%, and 263.1%, respectively. Hard WC particles played a decisive role in enhancing tribological performance of the bionic unit. Full article

The paper shows the effect of using a lubricant in the form of an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆), on the tribological properties of a hydrogenated diamond-like coating (DLC) doped with tungsten a-C:H:W. The coatings were deposited on 100Cr6 steel by plasma-enhanced chemical vapor deposition PECVD. Tribological tests were carried out on a TRB³ tribometer in a rotary motion in a ball–disc combination. 100Cr6 steel balls were used as a counter-sample. Friction and wear tests were carried out for discs made of 100Cr6 steel and 100Cr6 steel discs with a DLC coating. They were performed under friction conditions with and without lubrication under 10 N and 15 N loads. The ionic liquid BMIM-PF₆ was used as a lubricant. Coating thickness was observed on a scanning microscope, and the linear analysis of chemical composition on the cross-section was analyzed using the EDS analyzer. The confocal microscope with an interferometric mode was used for analysis of the geometric structure of the surface before and after the tribological tests. The contact angle of the samples for distilled water, diiodomethane and ionic liquid was tested on an optical tensiometer. The test results showed good cooperation of the DLC coating with the lubricant. It lowered the coefficient of friction in comparison to steel about 20%. This indicates the synergistic nature of the interaction: DLC coating–BMIM-PF₆ lubricant–100Cr6 steel. Full article

Many components in industry are subjected to high loads during operation and therefore often do not reach their intended service life. Conventional steels frequently do not provide sufficient protection against wear and corrosion. One solution is to coat these components using methods like thermal spraying to apply cermet coatings such as Cr₃C₂-NiCr or WC-Co-Cr. In light of increasingly strict environmental regulations, more eco-friendly alternatives are needed, especially ones that use little or no Cr, Ni, Co, or W. Another alternative is the recycling of powder materials, which is the focus of this research project. This study investigated whether filter dust from an HVOF system could be used to develop a new coating suitable for use in applications requiring resistance to wear and corrosion. This is challenging as the filter dusts have heterogeneous compositions and irregular particle sizes. Nevertheless, this recycled material, referred to as “Green Cermets” (GCs), offers previously untapped potential that may also be of ecological interest. An established WC-Co-Cr coating served as a reference. In addition to friction wear and corrosion resistance, the study also examined particle size distribution, hardness, microstructure, and susceptibility to crack formation at the interface and inside the coating. Even though the results revealed a diminished performance of the GC coatings relative to the conventional WC-CoCr, they may still be applicable in various industrial applications. Full article