Search Results (81)

Commodity shocks can generate material cross-border exposure because energy, food, industrial metals, and critical minerals are essential inputs to production and consumption. This article develops a transparent, margin-based screening framework for eight commodity categories using 2024 WITS/UN Comtrade reporter-to-world top-country data. The empirical design combines export- and import-side concentration, normalized entropy, an explicit non-substitutability scenario parameter, and a dimensionless trade-scale adjustment. A maximum-entropy independence matrix, $p_{ij}^k = e_i^k m_j^k$, is retained only as a null exposure benchmark; because it is rank one and contains no bilateral information beyond the observed margins, the study does not interpret it as a recovered trade network and does not report graph centrality. The revised results identify copper ores as the highest scale-adjusted vulnerability layer, followed by crude petroleum and liquefied natural gas; lithium carbonates remain highly concentrated but rank lower once trade scale is normalized dimensionlessly. Cobalt ores are retained only as a diagnostic illustration of HS-proxy fragility and are excluded from headline country rankings. Country-level tables report observed exporter and importer shares directly rather than redundant composite transmitter and receiver scores. Sensitivity analysis shows that the commodity ordering is robust to uniform and compressed non-substitutability scenarios and to broad parameter perturbations. Historical plausibility checks against the 2021–2022 European gas shock, Indonesia’s nickel-ore export restrictions, and the 2022 wheat disruption are directionally consistent with the screening signals, although they do not constitute causal validation. The framework is therefore intended as an early-warning screening device, not a graph-theoretic propagation model or a macroeconomic-loss estimate. Full article

In this study, an “oxide layer” was formed on the surface of Cu-0.97Cr-0.11Zr alloy sheets by introducing oxygen via a non-vacuum solid solution treatment, followed by vacuum solid solution and aging treatments to obtain a layered composite microstructure. The macro- and microstructures were characterized using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Furthermore, the properties of the alloy were evaluated through electrical conductivity and hardness measurements. The results indicate that during the non-vacuum solid solution process, oxygen atoms diffused into the copper alloy matrix and underwent an in situ oxidation reaction with the solute Cr. As the temperature increased from 800 °C to 900 °C, the thickness of the oxide layer grew from 23.2 μm to 77.8 μm. The formation of Cr₂O₃ nanophases within the oxide layer increased the alloy hardness from 87.3 HV to 101.8 HV and the electrical conductivity from 68.75% IACS to 78.85% IACS. Following subsequent vacuum solid solution and aging treatments, both hardness and electrical conductivity were significantly enhanced, reaching an edge hardness of 114.6 HV, a core hardness of 125.1 HV, and a conductivity of 80.32% IACS. Through this method, a layered composite structure of the Cu-0.97Cr-0.11Zr alloy, characterized by a highly conductive surface and a high-hardness core, can be successfully obtained. Full article

Miniaturized spatial electric field sensors often exhibit insufficient front-end charge coupling because of their limited sensing area. To address this material-level bottleneck, KH550-functionalized graphene composite films were developed as candidate electrode materials for spatial electric-field sensing. Single-layer and multilayer graphene powders were modified with the silane coupling agent KH550 and dispersed in a waterborne polyurethane/PVP matrix to fabricate composite films. The sensing mechanism was analyzed from the Maxwell–Wagner–Sillars interfacial polarization and electrode-equivalent capacitance perspectives. The modified materials were characterized by SEM, EDS, Raman spectroscopy, FTIR spectroscopy, low-frequency dielectric measurements, and broadband high-frequency impedance measurements. KH550 functionalization introduced Si- and N-containing surface species and increased disorder or sp³-related structural features while retaining the layered graphene structure. The film formulation selected through qualitative visual screening contained 0.16 g of graphene, 10 mL of waterborne polyurethane, and 0.05 g of PVP. Under AC excitation, the relative permittivity of the composite film containing KH550-functionalized multilayer graphene was approximately 18% higher than that of its unmodified counterpart. Broadband measurements showed material-dependent changes in the reflection and impedance responses of the electrode–fixture configurations. The modified multilayer-graphene electrode exhibited a different distribution of reflection minima, resistance maxima, and capacitive–inductive transitions from the unmodified and copper electrodes. Because the measured response includes contributions from the coating, substrate, fixture, and parasitic elements, these results are interpreted as comparative system-level responses. These results indicate that interfacial engineering of graphene composite films can enhance electrode-level dielectric response and charge-coupling capability, providing a material basis for non-contact electric field sensing electrodes. Full article

This study aims to reveal the formation mechanisms of typical defects in copper alloy castings and propose targeted process optimization strategies for production quality control. Taking the ZCuSn10P1 tin bronze outer layer of copper-clad iron core as the core research object, typical fracture and burr defects in actual mass production were systematically analyzed via multi-scale characterizations including SEM and EDS. Results show that fracture arises from abnormal Sn segregation and coarse hard-brittle δ phase, while burrs stem from insufficient matrix hardness during machining. Shrinkage cavity and porosity defects of aluminum bronze are further comparatively analyzed. A dual strategy of composition regulation and process optimization is put forward, which can effectively suppress defects and improve product qualification rate. This study provides a reliable reference for quality control and technical upgrading of copper alloy castings. Full article

Cu-based interpenetrating phase composites (IPCs) are candidate materials for sliding-contact applications in which thermal management, wear resistance, and electrical transport must be balanced. Herein, Cu–(CrW_x)C IPCs were fabricated by pressureless infiltration using nominal W-addition indices x = 0, 10, 25, and 50, corresponding to 0, 10, 25, and 50 g W added per 100 g Cr₂O₃ rather than final W mass fractions. Microstructural characterization indicates that W addition changes the scale and connectivity of W-containing carbide regions while preserving a continuous Cu-rich network. Representative quasi-static compression curves illustrate the large-strain load-bearing response but are interpreted descriptively because independent replicate specimens were not available for every composition under an identical test matrix. All composites retain room-temperature electrical conductivities of 39.23–40.44% of the International Annealed Copper Standard (IACS). Cu–(CrW10)C reaches a thermal conductivity of 208.27 W m⁻¹ K⁻¹ at 500 °C and the lowest specific wear rate of 2.42 × 10⁻⁶ mm³ N⁻¹ m⁻¹. Worn-surface and cross-sectional observations show that its low material loss coexists with localized cracking and adhered/detached features, whereas higher nominal W additions promote carbide fragmentation, interfacial separation, and hard-debris-mediated abrasion. The thermo-tribological performance index (TTPI) and electrical-thermal-wear balance index (ETWBI), used as internal screening metrics, identify Cu–(CrW10)C as the most balanced composition within the present four-composition dataset. These results demonstrate that wear resistance is governed by the stability of the skeleton-supported tribologically modified layer and continuous Cu-network transport rather than by hardness or nominal W addition alone. Full article

The paper investigates the structure and properties of titanium carbide-based composite coatings produced by flame spraying. The relevance of the study is associated with the need to improve the wear resistance and mechanical properties of components operating under abrasive and impact loading conditions in the metallurgical and machine-building industries. A composite powder mixture consisting of titanium carbide, copper, and aluminum was used as the coating material. Titanium carbide acted as a strengthening phase, while copper and aluminum served as damping and binding components. The coating was deposited onto a 30KhGS steel substrate using a 6 PM-II Powder Flame Spray System. Sedimentation analysis, scanning electron microscopy, energy-dispersive analysis, microhardness measurements, and wear resistance tests were carried out. The results demonstrated that the powder mixture has a predominantly fine-dispersed structure favorable for coating formation. The obtained coating exhibited a heterogeneous composite structure with uniformly distributed titanium carbide particles within the metallic matrix. The microhardness of the coating reached HV 770. Wear resistance tests showed insignificant weight loss after 10,000–30,000 abrasion cycles, indicating high wear resistance of the developed coating. It was established that the proposed composite composition contributes to the improvement of the strength characteristics, microhardness, and tribological properties of the surface layer. Full article

As a green energy technology, triboelectric nanogenerators (TENGs) convert mechanical energy into electricity and have gained significant attention in response to growing global environmental concerns. However, the widespread use of petroleum-based polymers as triboelectric materials in high-performance TENGs raises concerns over plastic pollution. In this work, we report a high-performance biodegradable TENG utilizing chitosan/laser-induced graphene (LIG) composite films as triboelectric layers. Modified chitosan substrates were first converted into LIGs via a convenient one-step CO₂ laser engraving, subsequently incorporated into chitosan matrices to form homogeneous composite films. A TENG device was designed by pairing the LIG/chitosan composite film with the fluorinated ethylene propylene (FEP) film, and copper electrodes. The introduction of LIG effectively strengthens charge storage and dielectric properties of the chitosan matrix, thereby significantly boosting the triboelectric output performance. Experimental results demonstrate that the as-assembled TENG with an LIG concentration of 1 wt.% achieves a peak open-circuit voltage of 196 V and short-circuit current of 2.1 μA, with a maximum power density of 295 mW/m². It can drive LED lights and small low-power electronic devices. Furthermore, the designed TENG device exhibits good biodegradability, flexibility, and stability, serving as a self-powered sensor for monitoring human joint movements. This work provides a simple and scalable strategy for integrating laser-induced graphene with biomass-based polymers, offering new insights into the design of high-performance, biobased triboelectric materials. Full article

MoS₂ acts as a high-performance lubricant, enhancing friction material stability, reducing wear and noise under extreme conditions, and preserving friction pair performance. However, its tendency to decompose and poor matrix wettability make surface modification essential for effective use in Cu-based composites. In this study, comprehensive investigations combining macro-scale and micro-scale friction experiments were conducted to examine the interfacial friction behavior of MoS₂ with different coatings and its tribological effects on copper-based composites under varying braking energy densities. The results indicate that the nickel coating suppressed MoS₂ decomposition, forming a high-strength diffusion interface with the matrix. This enhances the frictional stability and suppresses interfacial defect formation during micro-friction tests. However, the copper coating formed a poor-strength diffusion-reacting interface with matrix, leading to unstable friction at the interface and interface failure. Coating-dependent interfacial properties and micro-friction behaviors lead to varying tribological performance in Cu-based composites with MoS₂ during macro-friction tests. Nickel-plated MoS₂ (MoS₂@Ni) exhibits superior lubrication and frictional stability. The friction coefficients of Cu-based composites with MoS₂@Ni under low, medium and high working conditions are 0.36, 0.3 and 0.24, respectively, which are 6%, 12% and 13% lower than those of copper-plated MoS₂ (MoS₂@Cu). Meanwhile, its friction stability is 0.8, 0.6 and 0.58, respectively. With rising braking energy density, wear in Cu-based composites transitions from ploughing to oxidation and then to delamination. Defective MoS₂@Cu/matrix interfaces intensify delamination wear caused by the unstable fracture of subsurface plastic deformation layer cracks at higher energy density. Full article

When fabricating high-entropy alloy particle-reinforced metal matrix composites via friction stir processing, the relatively low heat input led to insufficient interfacial diffusion between the particles and matrix, thereby compromising the composite properties. To address this issue, this study introduced an electroless copper plating step followed by heat treatment to produce Cu-coated HEA particles with an interfacial diffusion layer. These modified particles were then incorporated into a copper matrix via friction stir processing to form composites with an intentionally designed interfacial diffusion layer. The results indicate that the diffusion layer structure contributed to excellent interfacial bonding. The resulting composite exhibited a simultaneous enhancement in both strength and ductility. The tensile strength and elongation reached 372.5 MPa and 34.2%, respectively, representing increases of 20.4% and 54% compared to pure copper. The wear rate of the composite reduced by 33.7% relative to pure copper. Quantitative analysis indicated that the contribution of fine-grain strengthening, Orowan strengthening, dislocation strengthening, and load transfer strengthening to the overall strength was 41.2 MPa, 0.3 MPa, 12.7 MPa, and 15.7 MPa, respectively. Full article

Alumina (Al₂O₃) reinforced copper matrix composites are widely used in the electronic industry, rail transit, and other fields due to their excellent electrical conductivity, ductility, and wear resistance. However, due to problems such as non-wetting and thermal expansion differences between alumina and Cu, weak interfacial bonding can easily reduce physical and thermal properties. A uniform silver layer was deposited on Al₂O₃ via chemical plating to enhance interface bonding with copper. Al₂O₃@Ag/Cu composites with 1–3 wt.% Al₂O₃ were prepared by rapid hot-press sintering. The effects of plating temperature and Al₂O₃ content on microstructure and properties were investigated. The results show that the optimum coating temperature is 25 °C, and a thin and uniform silver coating can be formed. This effectively improved Al₂O₃–Cu interface bonding while maintaining 77.8% of copper’s thermal conductivity (320.7 W/(m·K)). The composites showed improved wear resistance with increasing Al₂O₃ content. At 3 wt.% Al₂O₃@Ag, the wear rate was 3.36 × 10⁻⁵ mm³/(N·m), 84.4% lower than pure copper, with plow groove wear as the main mechanism. Full article

Tantalum nitride (TaN) coatings are valued for their hardness, chemical inertness, and biocompatibility; however, they lack intrinsic antibacterial properties, which limits their application in biomedical environments. Introducing copper (Cu) into the TaN matrix offers a potential solution by combining TaN’s mechanical and chemical durability with Cu’s well-documented antimicrobial action. This study explores how varying copper incorporation affects the structural, electrical, photocatalytic, and antibacterial characteristics of TaCuN multilayer films synthesized via reactive magnetron sputtering. Three thin TaCuN films were fabricated using a high-power reactive magnetron co-sputtering system, varying the Cu target power to control the composition. Structural and morphological analysis was performed using X-ray diffraction (XRD), scanning/transmission electron microscopy (STEM/TEM), and energy-dispersive X-ray spectroscopy (EDS). Electrical conductivity was studied along and across the film surfaces at temperatures ranging from 20 to 375 K using AC impedance spectroscopy. Optical and photocatalytic properties were assessed using UV–Vis spectroscopy and methylene blue degradation tests. Antibacterial activity against Staphylococcus aureus was analyzed under visible light using CFU reduction tests. XRD and TEM analyses revealed a multilayered four-zone architecture with alternating Ta-, Cu-, and N-rich phases and a dominant cubic δ-TaN pattern. The layers exhibited pronounced conductivity anisotropy, with in-plane conductivity (~10³ Ω⁻¹ cm⁻¹) exceeding cross-plane conductivity by ~10⁷ times, attributed to the formation of a metallic conduction channel in the mid-layer. Optical spectra indicated limited light absorption above 300 nm and negligible photocatalytic activity. Increasing the Cu content substantially enhanced antibacterial efficiency, with the highest-Cu sample achieving 95.6 % bacterial growth reduction. Morphological evaluation indicated that smooth film surfaces (Ra < 0.2 μm) effectively minimized bacterial adhesion. Reactive magnetron sputtering enables the precise engineering of TaCuN multilayers, combining high electrical anisotropy with robust antibacterial functionality. The optimized TaCuN coating offers promising potential in biomedical and protective applications where both conductivity and microbial resistance are required. Full article

Given the critical role of valve guides in the performance and lifespan of automotive engines, it is crucial to understand and improve their wear resistance. This study focuses on the wear resistance of powder metallurgy valve guides, aiming to systematically analyze the intrinsic relationship between their composition, microstructure, and properties. Three powder metallurgy valve guide samples with different compositions—specifically, a high-MoS₂ Fe-C-Mo-Cu-S alloy (1.5 wt.% C, 1.9 wt.% Mo, 1.5 wt.% Cu, 1.4 wt.% S), a low-MoS₂ Fe-C-Mo-Cu-S alloy (1.2 wt.% C, 0.3 wt.% Mo, 0.8 wt.% Cu, 0.2 wt.% S), and a Mo-free high-C-Cu Fe-C alloy (1.8 wt.% C, 5 wt.% Cu, 0 wt.% Mo, 0.01 wt.% S)—were studied using field emission scanning electron microscopy, metallographic microscopy, a reciprocating friction testing machine, and a 3D optical profilometer. The results show that the friction coefficient of the high-MoS₂ Fe-C-Mo-Cu-S alloy is the highest at 0.5, the low-MoS₂ Fe-C-Mo-Cu-S alloy is 0.25, and the Mo-free high-C-Cu Fe-C alloy is the lowest at 0.22. Since the minor wear amount cannot be accurately measured by the gravimetric method, the concave area of the wear-induced average roughness curve is employed to qualitatively indicate the magnitude of material loss: the area of the high-MoS₂ Fe-C-Mo-Cu-S alloy is 2964 μm², the low-MoS₂ Fe-C-Mo-Cu-S alloy is 1580 μm², and the Mo-free high-C-Cu Fe-C alloy is 1502 μm². The hardness results of the material show that the high-MoS₂ Fe-C-Mo-Cu-S alloy reaches 154 HB, the low-MoS₂ Fe-C-Mo-Cu-S alloy is 134 HB, and the Mo-free high-C-Cu Fe-C alloy is 145 HB. The porosity results show a difference of about 2% among the three alloys. Based on the microstructure characterization results, it can be concluded that the Mo-free high-C-Cu Fe-C alloy—with high carbon (C) and copper (Cu) content and fine pearlite layers—exhibits excellent wear resistance: high C can improve the hardness of the matrix, while Cu can act as a lubricating phase to enhance the material’s wear resistance. In contrast, although the addition of MoS₂ is intended to improve wear resistance, the irregular pearlite generated by MoS₂ reduces the wear resistance of the high-MoS₂ and low-MoS₂ Fe-C-Mo-Cu-S alloys; among them, the high-MoS₂ Fe-C-Mo-Cu-S alloy contains a higher amount of MoS₂, and large chunks appearing in the tissue easily cause abrasive wear and aggravate material wear during friction. This study provides solid theoretical and practical support for the material selection and performance optimization of powder metallurgy engine valve guides: the identified intrinsic relationship between alloy composition (MoS₂, C, and Cu contents), microstructure (pearlite morphology and second-phase distribution), and tribological performance establishes a clear theoretical basis for regulating the wear resistance of such components. Full article

Flexible pressure sensors are essential for wearable electronics, human–machine interfaces, and soft robotics. However, conventional Polydimethylsiloxane (PDMS)-based sensors often suffer from limited conductivity, poor filler dispersion, and low structural integration with textile substrates. In this work, we present a robotic drop-coating approach for fabricating graphite–copper nanoparticle (G-CuNP)/PDMS composite pressure sensors with textile-integrated electrodes. By precisely controlling droplet deposition, a three-layer sandwiched structure was realized that ensures uniformity and scalability while avoiding the drawbacks of conventional full-line coating. The effects of filler loading and graphite nanoparticle (GNP) and copper nanoparticle (CuNP) ratios were systematically investigated, and the optimized sensor was obtained at 40 wt% total fillers with a graphite content of 55 wt%. The fabricated device exhibited high sensitivity in the low-pressure region, stable performance in the medium- and high-pressure ranges, and an exponential saturation fitting with R² = 0.998. The average hysteresis was 7.42%, with excellent cyclic stability over 1000 loading cycles. Furthermore, a hand-shaped sensor matrix composed of five distributed sensing units successfully distinguished grasping behaviors of lightweight and heavyweight objects, demonstrating multipoint force mapping capability. This study highlights the advantages of robotic drop-coating for scalable fabrication and provides a promising pathway toward low-cost, reliable, and wearable soft pressure sensors. Full article

Although total knee replacements have an insignificant impact on patients’ mobility and quality of life, real-time performance monitoring remains a challenge. Monitoring the load over time can improve surgery outcomes and early detection of mechanical imbalances. Triboelectric nanogenerators (TENGs) present a promising approach as a self-powered sensor for load monitoring in TKR. A TENG was fabricated with dielectric layers consisting of Kapton tape and 3D-printed thermoplastic polyurethane (TPU) matrix incorporating CNT and BTO fillers, separated by an air gap and sandwiched between two copper electrodes. The sensor performance was optimized by varying the concentrations of BTO and CNT to study their effect on the energy-harvesting behavior. The test results demonstrate that the BTO/TPU composite that has 15% BTO achieved the maximum power output of 11.15 μW, corresponding to a power density of 7 mW/m², under a cyclic compressive load of 2100 N at a load resistance of 1200 MΩ, which was the highest power output among all the tested samples. Under a gait load profile, the same TENG sensor generated a power density of 0.8 mW/m² at 900 MΩ. By contrast, all tested CNT/TPU-based TENG produced lower output, where the maximum generated apparent power output was around 8 μW corresponding to a power density of 4.8 mW/m², confirming that using BTO fillers had a more significant impact on TENG performance compared with CNT fillers. Based on our earlier work, this power is sufficient to operate the ADC circuit. Furthermore, we investigated the durability and sensitivity of the 15% BTO/TPU samples, where it was tested under a compressive force of 1000 N for 15,000 cycles, confirming the potential of long-term use inside the TKR. The sensitivity analysis showed values of 37.4 mV/N for axial forces below 800 N and 5.0 mV/N for forces above 800 N. Moreover, dielectric characterization revealed that increasing the BTO concentration improves the dielectric constant while at the same time reducing the dielectric loss, with an optimal 15% BTO concentration exhibiting the most favorable dielectric properties. SEM images for BTO/TPU showed that the 10% and 15% BTO/TPU composites showed better morphological characteristics with lower fabrication defects compared with higher filler concentrations. Our BTO/TPU-based TENG sensor showed robust performance, long-term durability, and efficient energy conversion, supporting its potential for next-generation smart total knee replacements. Full article

Cu-20Pb-5Sn/45 steel bimetallic composites were prepared using the solid–liquid composite method. The interfacial microstructure, bonding strength, and wear performance were systematically characterized to elucidate the mechanisms governing the solid-solution interface and copper alloy layer wear behavior. The results reveal that mutual diffusion of Cu and Fe forms a metallurgically bonded α-(Cu,Ni)/α-Fe interface with a diffusion layer thickness of approximately 10.7 µm and an interfacial shear strength of 227.58 MPa. Under dry sliding conditions, the average coefficient of friction was 0.145, with a wear rate of 7.3665 × 10⁻⁶ mm³/(N·m). The α-(Cu,Ni) matrix was reinforced by hard Cu₃P and Ni-rich phases, which resist frictional shear stresses, while dispersed Pb particles provide self-lubricating properties, while the solid-solution interface hindered dislocation propagation, reducing dislocation pile-up and ensuring stable frictional performance. Full article