Search Results (1,395)

Graphene is considered one of the most promising flexible transparent electrode materials as it has high charge carrier mobility, high electrical conductivity, low optical absorption, excellent mechanical strength, and good bendability. However, graphene-based flexible transparent electrodes face a critical challenge in balancing electrical conductivity and optical transmittance. Here, we present a green and scalable direct ink writing (DIW) strategy to fabricate graphene grid patterns by optimizing ink formulation with sodium dodecyl sulfate (SDS) and ethanol. SDS eliminates the coffee ring effect via Marangoni flow, while ethanol enhances graphene flake alignment during hot-pressing, achieving a high conductivity of 5.22 × 10⁵ S m⁻¹. The grid-patterned graphene-based flexible transparent electrodes exhibit a low sheet resistance of 21.3 Ω/sq with 68.5% transmittance as well as a high stability in high-temperature and corrosive environments, surpassing most metal/graphene composites. This method avoids toxic solvents and high-temperature treatments, demonstrating excellent stability in harsh environments. Full article

Textured Si₃N₄/BN composite ceramics were successfully fabricated using two-step sintering, combining pseudo-hot isostatic pressing (PHIP) and gas pressure sintering. The grain size of h-BN platelets had a significant influence on densification and mechanical and thermal properties. With an increase in h-BN grain size, the volume density of the composite ceramics gradually decreased, while flexural strength gradually increased. Meanwhile, larger h-BN platelets were more likely to trigger toughening mechanisms like large-angle deflection and greatly increase fracture toughness. Through proper selection of h-BN grain size, textured ceramics, with the addition of h-BN platelets of 1–2 μm, showed high thermal conductivity (∼92 W∙m⁻¹∙K⁻¹) and reliable mechanical properties (∼540 MPa, ∼7.5 MPa∙m^1/2, ∼11.1 GPa). Therefore, texture control is an effective means of improving the overall performance of ceramic materials. Novel textured composite ceramics thus have great potential in large-scale fabrication and directional heat dissipation applications. Full article

Paper’s inherent hydrophilicity and porosity cause inadequate barrier properties, failing under high humidity/temperature. This study successfully developed a hydrophobic nanocoating agent (xLNPs-OTS) through silanization modification using D276 (lignin nanoparticles with a diameter of 276 nm) as the substrate and OTS (octadecyltrichlorosilane) as the functionalizing agent. By applying the coating to paper surfaces followed by a hot-pressing process, the paper achieved comprehensive performance enhancements, including superior water, oil, and vapor barrier properties, thermal stability, mechanical strength, frictional resistance, and self-cleaning capabilities. The Cobb 60 value of LOTSC3.5T120t30 (the coating made from the OTS silanized lignin with the coating amount of 3.5 g/m² and a hot-pressing at 120 °C for 30 min) coated paper is as low as 3.75 g/m², and can withstand hot water at 100 °C for 60 min. The Cobb 60 value of the LOTSC20T120t30 (the coating made from the OTS silanized lignin with the coating amount of 20 g/m² and a hot-pressing at 120 °C for 30 min) coated paper is reduced to 0.9 g/m², the Kit grade is 6, and all coated papers are endowed with self-cleaning features. This study advances lignin’s high-value utilization, driving sustainable packaging and supporting eco-friendly paper material development. Full article

Selective laser melting (SLM) offers a novel approach for manufacturing intricate structures, broadening the application of titanium alloy parts in the aerospace industry. After the build period, heat treatments of annealing (AT) and hot isostatic pressing (HIP) are often implemented, but a comparison of their mechanical performances based on the specimen orientation is still lacking. In this study, horizontally and vertically built Ti6Al4V SLM specimens that underwent the aforementioned treatments, together with their microstructural and defect characteristics, were, respectively, investigated using metallography and X-ray imaging. The mechanical properties and failure mechanism, via fracture analysis, were obtained. The critical factors influencing the mechanical properties and the correlation of the fatigue lives and failure origins were also estimated. The results demonstrate that the mechanical performances were determined by the α-phase morphology and defects, which included micropores and fewer large lack-of-fusion defects. Following the coarsening of the α phase, the strength decreased while the plasticity remained stable. With the discrepancy in the defect occurrence, anisotropy and scatter of the mechanical performances were introduced, which was significantly alleviated with HIP treatment. The fatigue failure origins were governed by defects and the α colony, which was composed of parallel α phases. Approximately linear relationships correlating fatigue lives with the X-parameter and maximum stress amplitude were, respectively, established in the AT and HIP states. The results provide an understanding of the technological significance of the evaluation of mechanical properties. Full article

This work investigates the effect of nanoclay addition—specifically natural montmorillonite (MMT) and organo-modified montmorillonite (O-MMT)—on the elastocaloric performance of natural rubber (NR), a promising material for solid-state cooling due to its non-toxicity, low cost, and ability to exhibit large adiabatic temperature changes under moderate stress (~a few MPa). Despite these advantages, the cooling efficiency of NR remains lower than that of conventional vapor-compression systems. Therefore, improving the cooling capacity of NR is essential for the development of solid-state cooling technologies competitive with existing ones. To address this, two series of NR-based nanocomposites, containing 1, 3, and 5 phr nanofiller, were prepared by melt compounding and hot pressing and characterized in terms of morphology, thermal, mechanical, and elastocaloric properties. The results highlighted that the better dispersion of the organoclays within the rubber matrix promoted not only a better mechanical behavior (in terms of stiffness and strength), but also a significantly enhanced cooling performance compared to MMT nanofilled systems. Moreover, NR/O-MMT samples demonstrated up to a ~45% increase in heat extracted per refrigeration cycle compared to the unfilled NR, with a coefficient of performance (COP) up to 3, approaching the COP of conventional vapor-compression systems, typically ranging between 3 and 6. The heat extracted per refrigeration cycle of NR/O-MMT systems resulted in approx. 16 J/cm³, higher with respect to the values reported in the literature for NR-based systems (ranging between 5 and 12 J/cm³). These findings emphasize the potential of organoclays in enhancing the refrigeration potential of NR for novel state cooling applications. Full article

The improvement of densification and fracture toughness in high-entropy ceramics is important to realizing their practical applications. In this study, SiC whiskers and metal Ni additions were incorporated to solve these problems of high-entropy boride ceramics. The influence of sintering temperatures (1450–1650 °C) on the densification, microstructure, hardness, fracture toughness, and bending strength of (M_0.2Ti_0.2Ta_0.2V_0.2Nb_0.2)B₂-SiC_w-Ni (M=Hf, Zr, or Cr) composites prepared by hot-pressing technology were studied. Results showed that when SiC whiskers and metal Ni additions were used as additives, increasing sintering temperatures from 1450 to 1600 °C promoted the densification of high-entropy boride ceramics. This was mainly attributed to the high sintering driving force. However, when the temperature further increased to 1650 °C, their densification behavior decreased. At a sintering temperature of 1600 °C, these high-entropy borides ceramics all had the highest densification behavior, leading to their high hardness and fracture toughness. The highest relative density was 96.3%, the highest hardness was 22.02 GPa, and the highest fracture toughness was 13.25 MPa·m^1/2, which was improved by the co-function of SiC whiskers and plastic metal Ni. Meanwhile, in the adopted sintering temperature range of 1450 to 1650 °C, the highest bending strength at room temperature of these high-entropy boride ceramics could reach 320.8 MPa. Therefore, this research offers an effective densification, strengthening, and toughening method for high-entropy boride composites at a low sintering temperature. Full article

This study fabricated SrTiO₃ grain boundary layer ceramics using hot isostatic pressing (HIP), achieving a remarkably high dielectric constant of 60,350 and a superior breakdown strength of 1722 kV/m. Microstructural characterization via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that HIP treatment significantly refined grain size uniformity and homogenized bismuth distribution at grain boundaries, thus enhancing the interfacial barrier effect. Probe-based impedance spectroscopy elucidated the dielectric behavior and conduction mechanisms of individual grain boundaries. HIP promotes the formation of interfacial barrier layers (IBLs), significantly improving electrical performance. Compared to untreated samples (average breakdown strength: 555 kV/m), HIP-processed ceramics exhibited a threefold enhancement in breakdown strength (1722 kV/m). The treated ceramic exhibited excellent temperature stability, with TCC ≤8% over −55 to 125 °C. The optimized dielectric properties stem from HIP-induced structural modifications, including reduced oxygen vacancy concentrations and homogenized electronic distribution at grain boundaries. These findings establish a quantitative correlation between HIP parameters, grain boundary restructuring, and macroscopic performance, providing critical insights for designing high-energy-density dielectric materials. Full article

The cast nickel-based superalloy K417G exhibits excellent high-temperature strength, but non-equilibrium solidification during casting can cause defects such as irreparable interdendritic microporosity, which significantly degrades its fatigue and creep properties. This study uses hot isostatic pressing (HIP) to eliminate internal flaws such as porosity in the K417G alloy, aiming to improve its mechanical properties. We investigated the microstructure and mechanical properties of K417G under two thermal conditions: solution heat treatment (SHT) and hot isostatic pressing (HIP). The results indicate that HIP significantly reduces microporosity. Compared to SHT, HIP improves the mechanical performance of K417G. The creep fracture mechanism shifts from intergranular brittle fracture (SHT) to ductile fracture (HIP). Consequently, HIP increases the alloy′s creep life approximately threefold and raises its fatigue limit by about 20 MPa. This improvement is attributed to pore density reduction, which decreases stress concentration zones and homogenizes the microstructure, thereby impeding fatigue crack nucleation and extending the crack incubation period. Full article

This study examines the corrosion characteristics of GRX-810, a NiCoCr-based high entropy alloy, in a simulated marine environment represented by 3.5 wt.% NaCl solution. The research employs electrochemical and surface analysis techniques to evaluate the corrosion performance and protective mechanisms of this alloy. Electrochemical characterization was performed using potentiodynamic polarization to determine critical corrosion parameters, including corrosion potential and current density, along with electrochemical impedance spectroscopy to assess the stability and protective qualities of the oxide film. Surface analytical techniques provided detailed microstructural and compositional insights, with scanning electron microscopy revealing the morphology of corrosion products, energy-dispersive X-ray spectroscopy identifying elemental distribution in the passive layer, and X-ray diffraction confirming the chemical composition and crystalline structure of surface oxide. The results demonstrated distinct corrosion resistance behavior between the different processing conditions of the alloy. The laser powder bed fused (LPBF) specimens in the as-built condition exhibited superior corrosion resistance compared to their hot isostatically pressed (HIPed) counterparts, as evidenced by higher corrosion potentials and lower current densities. Microscopic examination revealed the formation of a dense, continuous layer of corrosion products on the alloy surface, indicating effective barrier protection against chloride ion penetration. A compositional analysis of all samples identified oxide film enriched with chromium, nickel, cobalt, aluminum, titanium, and silicon. XRD characterization confirmed the presence of chromium oxide (Cr₂O₃) as the primary protective phase, with additional oxides contributing to the stability of the film. This oxide mixture demonstrated the alloy’s ability to maintain passivity and effective repassivation following film breakdown. Full article

Under the global initiative for automotive lightweighting to address climate challenges, this study investigates the microstructure evolution of steel–aluminum composites processed by hot equal-channel angular pressing (H-ECAP). Using 6061-T6 aluminum cores clad with 20 # low carbon steel tubes processed through 1–4 C-path passes (Φ = 120°, ψ = 30°), we demonstrate significant microstructural improvements. The steel component showed progressive grain refinement from 2.2 μm (1 pass) to 1.3 μm (4 pass), with substructures decreasing from 72.19% to 35.46%, HAGB increasing from 31.2% to 34.6%, and hardness increasing from 222 HV to 271 HV. Concurrently, aluminum experienced grain refinement from 59.3 μm to 28.2 μm, with recrystallized structures surging from 0.97% to 71.81%, HAGB increasing from 9.96% to 63.76%, and hardness increasing from 51.4 HV to 83.6 HV. The interfacial layer thickness reduced by 74% (29.98 μm to 7.78 μm) with decreasing oxygen content, containing FeAl₃, Fe₂Al₅, and minimal matrix oxides. Yield strength gradually increased from 361 MPa (one pass) to 372.35 MPa (four passes), accompanied by a significant enhancement in compressive strength. These findings reveal that H-ECAP’s thermomechanical coupling effect effectively enhances interface bonding quality while suppressing detrimental intermetallic growth, providing a viable solution to overcome traditional manufacturing limitations in steel–aluminum composite applications for sustainable mobility. Full article

Chitosan films with potential application in triboelectric nanogenerators (TENGs) represent a promising approach to replace non-biobased materials in these innovative devices. In the present work, chitosan with varying molecular weights (MW) and degrees of deacetylation was dissolved in aqueous acetic acid (AA) at different acid concentrations. It was observed that the MW had a greater influence on the viscosity of the solution compared to either the acid concentration or deacetylation degree. Gel formation occurred in high-MW chitosan solutions prepared with low AA concentration. Films prepared from chitosan solutions, through solvent-casting, were used to prepare TENGs. The power output of the TENGs increased with higher concentrations of AA used in the chitosan dissolution process. Similarly, the residual AA content in the dried films also increased with higher initial AA concentrations. Additionally, hot-pressing of the films significantly improves the TENG power output due to the decrease in morphological defects of the films. It was demonstrated that a good selection of the acid concentration not only facilitates the dissolution of chitosan but also plays a key role in defining the properties of the resulting solutions and films, thereby directly impacting the performance of the TENGs. Full article

This study systematically investigates the effects of heat treatment at 800–1000 °C on the microstructure and mechanical properties of 10 wt.% TiB₂@Ti/AlCoCrFeNi_2.1 eutectic high-entropy alloy matrix composites (EHEAMCs) prepared by vacuum hot-pressing sintering. The results show that the materials consist of FCC, BCC, TiB₂, and Ti phases, with a preferred orientation of the (111) crystal plane of the FCC phase. As the temperature increases, the diffraction peak of the BCC phase separates from the main FCC peak and its intensity increases, while the diffraction peak positions of the FCC and BCC phases shift at small angles. This is attributed to the diffusion of TiB₂@Ti from the grain boundaries into the matrix, where the Ti solid solution increases the lattice constant of the FCC phase. Microstructural observations reveal that the eutectic region transforms from lamellar to island-like structures, and the solid solution zone narrows. With increasing temperature, the Ti concentration in the solid solution zone increases, while the contents of elements such as Ni decrease. Element diffusion is influenced by binary mixing enthalpy, with Ti and B tending to solidify in the FCC and BCC phase regions, respectively. The mechanical properties improve with increasing temperature. At 1000 °C, the average hardness is 579.2 HV, the yield strength is 1294 MPa, the fracture strength is 2385 MPa, and the fracture strain is 19.4%, representing improvements of 35.5% and 24.9% compared to the as-sintered state, respectively, without loss of plasticity. The strengthening mechanisms include enhanced solid solution strengthening due to the diffusion of Ti and TiB₂, improved grain boundary strength due to the diffusion of alloy elements to the grain boundaries, and synergistic optimization of strength and plasticity. Full article

The constitutive model significantly influences the accuracy of predicting the complex rheological behavior of hot isostatically pressed powders. The temperature plays a crucial role in determining material properties during hot isostatic pressing (HIP), making it essential to account for its effect on the yield model parameters to more accurately describe the densification evolution of powders. In this study, HIP experiments were conducted using two different process schemes, and the shrinkage deformation of the envelope under each scheme was analyzed. High-temperature uniaxial compression experiments were performed on HIP samples with varying densities to analyze and characterize the stress–strain response of the powder during HIP. A mesoscopic particle-scale high-temperature uniaxial compression model was developed based on the discrete element method (DEM), and the strain and stress values corresponding to different densities in the high-temperature uniaxial compression simulations were validated through experimental comparison. The strain evolution during the uniaxial compression process was analyzed, and the relationship between the parameters of the Shima–Oyane model and the temperature was established, leading to the development of a temperature-compensated Shima–Oyane model. Based on the obtained parameters at various densities and temperatures, a yield stress map for the nickel-based alloy was constructed. The accuracy of this model was verified by comparing experimental results with finite element method (FEM) simulations. The findings of this study contribute to a more precise prediction of densification behavior in thermally driven isostatic pressing. Full article

The advent of additive manufacturing (AM), also known as 3D printing, has revolutionized the production of titanium alloys, offering significant advantages in fabricating complex geometries with enhanced mechanical properties. This study investigates the variant-specific deformation mechanisms in HIP-treated TA15 (Ti-6.5Al-2Zr-1Mo-1V) titanium alloy, fabricated via selective electron beam melting (SEBM). The alloy exhibits a dual-phase (α+β) microstructure, where six distinct α variants are formed through the β→α phase transformation following the Burgers orientation relationship. Variant selection during AM leads to a non-uniform distribution of these α variants, with α6 (22.3%) dominating due to preferential growth. Analysis of the prismatic slip Schmid factor reveals that α4–α6 variants, with higher Schmid factors (>0.45), primarily undergo prismatic slip, while α1–α3 variants, with lower Schmid factors (<0.3), rely on basal or pyramidal slip and twinning for plastic deformation. In-grain misorientation axis (IGMA) analysis further reveals strain-dependent slip transitions: pyramidal slip is activated in α1–α3 variants at lower strains, while prismatic slip becomes the dominant deformation mechanism in α4–α6 variants at higher strains. Additionally, deformation twins, primarily {10–12}<1–101> extension twins (7.1%), contribute to the plasticity of hard-oriented α variants. These findings significantly enhance the understanding of the orientation-dependent deformation mechanisms in HIPed TA15 alloy and provide a crucial basis for optimizing the performance of additively-manufactured titanium alloys. Full article

Eskebornite (CuFeSe₂), a member of the I–III–VI₂ ternary semiconductor family, was explored in this study as a potential thermoelectric material, offering new insights into its synthesis, structural characteristics, and transport behavior. Structurally analogous to chalcopyrite (CuFeS₂)—an extensively studied antiferromagnetic semiconductor—eskebornite remains relatively underexplored, particularly regarding its solid-state synthesis and thermoelectric performance. To address this gap, pure eskebornite was synthesized via mechanical alloying followed by hot pressing, a method that enables the fine control of its phase composition and microstructural features. The synthesized undoped CuFeSe₂ exhibited p-type nondegenerate semiconducting behavior, with electrical conductivity increasing monotonically over the temperature range of 323–623 K, indicative of thermally activated carrier transport. Simultaneously, a decreasing trend in thermal conductivity with temperature was observed, likely resulting from intensified phonon scattering, which serves to suppress heat transport and enhance the thermoelectric efficiency by maintaining a thermal gradient across the material. A peak in the Seebeck coefficient occurred between 473 and 523 K, suggesting the onset of intrinsic carrier excitation and a transition in dominant carrier transport mechanisms. The material exhibited a maximum power factor of 1.55 μWm⁻¹K⁻², while the dimensionless thermoelectric figure of merit (ZT) reached a peak value of 0.37 × 10⁻³ at 523 K. Although the ZT remains low, these results underscore the potential of eskebornite as a thermoelectric candidate, with substantial room for optimization through chemical doping, microstructural engineering, or nanostructuring approaches to enhance the carrier mobility and reduce the lattice thermal conductivity. Full article