Gradient Layer Research Articles

Distribution pattern of soil nematode communities along an elevational gradient in arid and semi-arid mountains of Northwest China.

Soil nematodes are the most abundant soil metazoans, occupying multiple trophic levels in the soil food web and playing an important role in soil function. Research on the biogeographic distribution patterns of soil nematode communities and their drivers has received greater attention. However, the distribution characteristics of soil nematode communities along the elevational gradient in the arid and semi-arid regions of Northwest China remain unclear. In this study, four elevational gradients (1750-1900, 1900-2100, 2100-2350 and 2350-2560 m) were established on Luoshan Mountain, Ningxia, an arid and semi-arid region in Northwest China, and soil nematodes in the soil layers of 0-10, 10-20 and 20-40 cm were investigated using the improved Baermann funnel method. The results revealed a monotonically decreasing trend in the total number of soil nematodes along the elevational gradient and soil layer depth, decreasing by 63.32% to 79.94% and 73.59% to 86.90%, respectively, while the interactions were not obvious. A total of 1487 soil nematodes belonging to 27 families and 32 genera were identified across the elevational gradient, with Helicotylenchus as the dominant genus, accounting for 10.43% of the total number of nematodes, and bacterivore nematodes as the main trophic groups, accounting for 32.39% to 52.55% of the relative abundance at each elevation, which increased with increasing elevation. Soil nematode community diversity, richness and maturity indices were relatively low at high elevation and decreased by 44.62%, 48% and 54.74%, respectively, with increasing soil layer depth at high elevations. Compared to low elevations, high-elevation soils experienced greater disturbance, reduced structural complexity and nutrient enrichment of the soil food web, and a shift in soil organic matter decomposition from bacterial to fungal pathways as elevation increased. Finally, redundancy analysis showed that soil pH, bulk density, soil moisture, soil organic carbon, available nitrogen, available phosphorus and available potassium were the main soil factors affecting the composition of soil nematode communities, which well explained the differences in nematode communities at different elevations and soil depths. This study can be used as basic information for further research on soil biota in this mountainous region, expanding our further understanding of the spatial ecology of soil nematodes in the arid and semi-arid mountain ecosystems.

Gradient distribution of cations in rhabdophane La0.27Y0.73PO4·nH2O nanoparticles

The structure of gradient rhabdophane nanoparticles of variable composition (La,Y)PO4·nH2O obtained by precipitation is considered. According to the data of HAADF TEM and EDX mapping using the Abel inversion procedure, it was shown that there is an inhomogeneous distribution of yttrium and lanthanum atoms in the particles from the central part to the periphery. At the same time, the nominal composition of both individual nanoparticles and the entire sample meets the value specified during synthesis within the error of the method – La0.27Y0.73PO4·nH2O. According to SAXS data, it was determined that in the particles of (La,Y)PO4·nH2O, there is a redistribution of scattering densities, which is caused by an increase in the fraction of YPO4 in the peripheral region of the particles. The observed effect of the distribution of cations over the particle made it possible to determine the size of the gradient layer, which reaches 50 % of the total particle size.

Incorporation of Graphene Oxide Quantum Dots in Gradient Layers of Polyethersulphone Nanofiltration Membranes for Nitrate Rejection from Aqueous Solution.

Graphene oxide quantum dots (GOQDs) have been widely used to prepare nanofiltration membranes due to the merits of excellent dispersity, ultrasmall size, and unique properties related to graphene. In this study, we first prepared the polyethersulphone-based nanofiltration (PES-NF) membrane via an interfacial polymerization process using a piperazine and m-phenylenediamine mixed solution as the aqueous phase. Then GOQDs were incorporated into the top-down gradient structured layers (i.e., ultrathin layer, interlayer, and substrate membrane layer) of the nanofiltration membrane, and subsequently the effect of GOQD addition on the nitrate rejection was evaluated. Compared with the pristine PES-NF membrane without the incorporation of GOQDs, the fabricated NF membrane (GOQD/PES-NF-2) incorporating GOQDs at both the ultrathin layer and interlayer exhibits more remarkable performances (an acceptable permeation flux of 52.2 L m-1 h-1 and excellent nitrate rejection of 96.3% at 0.6 MPa), the permeation flux of this membrane increases by nearly 2.4 times, and its nitrate rejection also shows a slight enhancement (∼7.6%) compared with those of PES-NF. Remarkably, at the operating pressure much lower than that required by reverse osmosis membranes, the GOQD/PES-NF-2 membrane possesses an equivalent monovalent ion rejection to reverse osmosis membranes but a higher permeation flux. Furthermore, the result of a 7 day continuous stability test validates the excellent durability of the GOQD/PES-NF-2 membrane, and its antifouling and chlorine resistance performances also outperform those of the PES-NF membrane.

Enhanced Fluorescence in Green ZnSeTe Quantum Dots Using Gradient Layer Technique

AbstractA novel method is presented for synthesizing green ZnSeTe quantum dots (QDs) that demonstrate high photoluminescence quantum yield (PLQY) and a narrow full width at half maximum (FWHM). In this synthesis, a gradient layer is created between the ZnSeTe core and the ZnSe inner shell by utilizing the different reactivities of precursors. This innovative approach aims to reduce lattice mismatch and minimize interfacial defects, thereby enhancing the fluorescence properties of ZnSeTe QDs. Using the gradient layer, green QDs are achieved with a FWHM of 36 nm and a PLQY of 90%, surpassing previous results. Detailed structural analyses confirmed a reduction in stacking faults and strain in the QDs with a gradient layer, leading to enhanced fluorescence properties. The QDs with a gradient layer are successfully integrated into the emissive layer of a quantum dot light–emitting diode device, demonstrating superior performance compared to QDs without the gradient layer.

Microstructure and performance of compositionally graded Ta2O5/Ti thin films on Ti6Al4V alloy deposited by magnetron sputtering

Tantalum pentoxide (Ta2O5) ceramic is a promising material for modifying metal implants due to its superior wear resistance, chemical stability, and biocompatibility. However, the clinical application of Ta2O5 coatings may be limited by inadequate adhesion, resulting from performance mismatches between Ta2O5 coatings and metal substrates. In this study, a Ta2O5/Ti gradient film was developed on the Ti6Al4V titanium alloy substrate using magnetron sputtering, consisting of a Ti bonding layer, four Ta2O5-Ti composite interlayers with graded composition, and a Ta2O5 surface layer. The microstructure and properties of the Ta2O5/Ti gradient films were investigated, with a Ta2O5 monolayer coating as a reference. Results reveal that the gradient layers have higher density, lower surface roughness, diminished residual thermal stress, and improved adhesion, mechanical properties, and wear resistance compared to the Ta2O5 monolayer coating. However, the corrosion resistance of the Ta2O5/Ti gradient layer sample is inferior to that of the Ta2O5 monolayer coating sample, attributed to interphase corrosion between Ta2O5 and Ti within the interlayers. These significant findings offer a promising approach for enhancing the overall performance of Ta2O5 coating on Ti6Al4V titanium alloy surfaces, thereby opening avenues for widespread application in the biomedical industry.

Effect of sintering cycle on the strength and translucency of multilayered zirconia.

A newly introduced sintering protocol promises to offer higher translucency while not significantly compromising the flexural strength of the material. However, the effect of the novel sintering protocol has not been thoroughly validated. The purpose of this study was to measure and compare the effect of two sintering protocols on the translucency and flexural strength of two multilayered zirconia materials. Two types of multilayered zirconia materials (ZirCAD Prime and Prime esthetic) were selected. Presintered disk specimens were obtained from Translucent, Gradient, and Dentin layers (n = 20). The disks were allocated to 2 groups: standard sintering protocol (peak temperature 1500°C) and high translucency sintering protocol (peak temperature 1600°C). After the sintering process, 10 specimens from each group were randomly selected. The optical values (L*, a*, b*) were measured and used to assess translucency using the relative translucency parameter (RTP00) and translucency differences (ΔRTP00). Then, all 20 specimens were tested for biaxial flexural strength. The outcomes were analyzed. The analysis of variance is used to analyze any significant effects on translucency and flexural strength. Then, any significant difference in the translucency and flexural strength between all pairs of materials was analyzed using Bonferroni-corrected Student's t-test (α = 0.05). The high translucency sintering protocol significantly decreased biaxial strength in the Prime translucent and dentine layer, Prime esthetic translucent, and gradient layer. RTP00 was significantly reduced in the Prime gradient and Prime esthetic gradient layer when sintered with a high translucency protocol. The lowest ΔRTP00 was observed in the Prime dentine layer, while the highest ΔRTP00 was observed in the Prime esthetic dentin layer. High translucency protocol significantly lowers the biaxial flexural strength of both multilayered materials, but the alteration in translucency is within clinically acceptable thresholds (TAT00 = 2.62).

Interface characteristics and performance of additively manufactured steel-titanium bimetals prepared through composition gradient layers

In this study, laser-directed energy deposition (LDED), a powder-feeding laser additive manufacturing technique, was utilized to fabricate bimetals comprising high-strength steel (HSS) and Ti6Al4V (TC4). Through meticulous compositional control, four distinct regions (labeled Areas 1 through 4) comprising Fe-Ti intermetallics with varying sizes and morphologies were obtained at the LDEDed HSS/TC4 interface. These zones exhibited thicknesses of approximately 190 μm, 210 μm, 525 μm, and 205 μm, respectively. The effect of these intermetallics on the performance of LDEDed HSS/TC4 bimetals was investigated. The results indicated that most Fe-Ti intermetallics, characterized by reticular/granular morphologies or fine precipitates, were dispersed at the bonded interfaces (Areas 1, 3, 4). Nevertheless, irregular and long-striped C14_Laves phases were observed in Area 2, indicating the presence of a pure Fe2Ti region. Performance testing revealed that fractures predominantly occurred within a hard and brittle Fe2Ti region (Hardness: 891.5HV) during mechanical grinding or tensile clamping, highlighting the formidable challenge of achieving high-quality LDEDed HSS/TC4 bimetals through a component-regulated building strategy. The difficulty arises from the high Fe content in HSS and high Ti content in TC4, resulting in the formation of a pure Fe2Ti region at the interface. Thermodynamic calculations suggest that the composition-gradient-layer strategy may not be optimal for the integrated laser additive manufacturing of HSS and TC4. These findings provide valuable insights into the design of steel-titanium functional gradient materials and other multi-material components.

Structural optimization and heat-fluid-solid simulation of a graded corundum-calcium hexaluminate purging plug by a multi-objective genetic algorithm approach

The purging plug is essential for enhancing production efficiency in molten steel refining, yet it faces challenges related to structural integrity due to its lifespan often not aligning with the ladle's repair cycle. This study introduces a novel corundum-calcium hexaluminate purging plug with gradual holes designed to alleviate internal stress concentration. Utilizing a multi-objective optimization model and fluid-solid coupling heat transfer method, the impact of structural parameters on thermal and mechanical properties was systematically investigated. The numerical simulation results indicate that increasing the number of gradient layers positively impacts temperature distribution. Notably, the D-210 (1.0 mm diameter) aperture reduces the stress gradient Δσmax by 648.06 MPa compared to D-212 (1.2 mm diameter) at the Y = 0.313 m section. Additionally, variation in inclination angle impacts tensile stress σt and shear stress τ, an inclination angle of 6° (α6) reduces maximum tensile stress by 211.41 MPa compared to an angle of 0° (α0).

Tuning the Permeation Properties of Poly(1‐trimethylsilyl‐1‐propyne) by Vapor Phase Infiltration Using Trimethylaluminum

AbstractVapor phase infiltration (VPI) has emerged as a promising tool for fabrication of novel hybrid materials. In the field of polymeric gas separation membranes, a beneficial impact on stability and membrane performance is known for several polymers with differing functional groups. This study for the first time investigates VPI of trimethylaluminum (TMA) into poly(1‐trimethylsilyl‐1‐propyne) (PTMSP), featuring a carbon–carbon double bond as functional group. Saturation of the precursor inside the polymer is already attained after 60 s infiltration time leading to significant densification of the material. Depth profiling proves accumulation of aluminum in the polymer itself, but a significantly increased accumulation is visible in the gradient layer between polymer and SiO2 substrate. A reaction pathway is proposed and supplemented by density‐functional theory (DFT) calculations. Infrared spectra derived from both experiments and simulation support the presented reaction pathway. In terms of permeance, a favorable impact on selectivity is observed for infiltration times up to 1 s. Longer infiltration times yield greatly reduced permeance values close or even below the detection limit of the measurement device. The present results of this study set a strong basis for the application of VPI on polymers for gas‐barrier and membrane applications in the future.

The Impact of Catalyst Layer Fabrication Procedure on Layer Morphology, Transport Properties and Performance in Low-Temperature PEM Fuel Cell

Hydrogen mobility represents a progressive, low carbon imprint option for the replacement of internal combustion engines. A core of this technology is low-temperature fuel cell with proton-exchange membrane (LTPEMFC), using hydrogen and atmospheric oxygen as fuel and oxidant, respectively. The membrane-electrode assembly (MEA) which makes up a cell consists of polymer electrolyte membrane, cathodic and anodic catalyst layers and carbon-based porous gas-diffusion layers. LTPEMFC require Pt catalyst on both the anode and the cathode in non-negligible total amount, increasing investing costs for stack unit. In order to maximise fuel cell performance, the formation of three-phase boundary has to be achieved during deposition of catalyst layers, interconnecting Pt nanoparticles on carbon support and ionomer with membrane in complex, porous structure. The quality of catalyst layer determines to high degree final MEA performance.Catalyst layers can be deposited either on gas-diffusion layers or onto the membrane, with latter being considered a more advantageous and feasible approach. Deposition itself can be realised by various methods, including airbrush spraying, decal printing, doctor blade deposition from paste and, most often used nowadays, ultrasonically-assisted spray coating. Each of these methods brings its own advantages and disadvantages, though the common problem of these methods is low suitability for serial production. On the other hand, the quality of so-prepared catalyst layers is sufficient. Methods for large-capacity coating of catalyst layers, especially roll-to-roll technology have exactly opposite pros and cons, high output but unsatisfactory layer quality. An interesting alternative to state-of-the-art catalyst layer fabrication procedures is inkjet printing.Inkjet printing is a well-established technology, though the application in LTPEMFC field brings various issues, mainly connected to quality of layers and prevention of nozzle-clogging during the deposition. Solving of these issues, however, will result in technology suitable for catalyst layer printing, combining high production throughput, very good reproducibility, minimal losses of the ink, suitability to additive manufacturing and possibility of printing specific geometries with gradient layer thickness. Accordingly, the goal of this study is the comparison of catalyst layers, deposited onto the membrane by ultrasonically-assisted spray coating and inkjet printing, in terms of morphology, electric conductivity, permeability and performance in LTPEMFC, using commercially-available materials for layer fabrication.Catalyst layers of the same composition and Pt loading were deposited by either ultrasonically-assisted spray coating or inkjet printing onto FTO conductive glass for the determination of electric conductivity, onto gas-diffusion layer for permeability determination in Loschmidt cell and FIB-SEM morphology studies and onto the membrane for the fabrication of MEA and evaluation of its performance in LTPEMFC. Characterisation of layers deposited on materials above underlined feasibility of inkjet printing for catalyst layer fabrication. In comparison with sprayed layers, layers prepared by inkjet printing tend to be thinner, more homogenous and compact. This results in superior electric conductivity but lower permeability at the same time. Single cell tests proved that performance of inkjet-printed layers is at least on par with sprayed ones, surpassing them with optimised ink composition and Pt loading. Overall, inkjet printing technology is a highly attractive technology for industrial catalyst layer production with great possibilities for contributing to decrease LTPEMFC unit’s investment costs.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 958174. This project is co-financed from the state budget by the Technology agency of the Czech Republic under the M-ERA.Net Programme, project No. TH80020006. This work was supported by the project "The Energy Conversion and Storage", funded as project No. CZ.02.01.01/00/22_008/0004617 by Programme Johannes Amos Commenius, call Excellent Research. This project is co-financed with tax funds on the basis of the budget passed by the Saxon state parliament.

Enhanced tribological properties and the microstructure evolution of the gradient nanostructured copper alloy

In this work, the effects of the gradient microstructures by surface mechanical attrition treatment (SMAT) on the corresponding tribological properties of the nanoprecipitates strengthened copper alloy was investigated. The nanoprecipitates strengthened copper alloy possesses a decent tribological properties compared with the pure copper and bronze. The SMAT-processed NP&T alloy possesses distinctly lower coefficients of friction (COF) than its coarse-grained counterpart throughout the entire frictions. In particular, under a sliding load of 2 N, NP&T alloy possesses a lower COF of 0.58 ± 0.03, approximately 15% lower than that of its homogeneous counterpart. Additionally, the wear volumes, wear rates, and worn surface roughness were approximately 45% lower in the NP&T alloy, indicating the superior tribological properties. The macro-, micro-, and atomic-scale friction and wear mechanisms in the worn NP&T alloy were systematically determined. The inherent gradient nanostructures could achieve strain delocalization, thereby suppressing surface deformation and improving wear resistance. Wear-induced substructure in the NP&T alloy comprises gradient layers mediated by twinning and stacking faults combined with nanocomposite layers, resulting in novel tribological performance characteristics. Thus, combining inherent and newly formed wear-resistant gradient nanostructures is an effective design strategy for high-performance Cu alloys.

Strategy for preparing nanocrystalline Ta-N gradient layer with enhanced mechanical and tribological performance via microwave plasma nitriding

Herein, microwave plasma nitriding (MPN) was employed to fabricate a nanocrystalline tantalum nitride (Ta–N) layer with enhanced mechanical and tribological performance. The results revealed that the nitrogen content in the Ta–N layer appeared as a gradient distribution, resulting in a component gradient structure comprising Ta2N, a solid solution of N in Ta and superlattice TaN0.04 from the top surface to the matrix, which was advantageous for relaxing the stress between the top Ta–N layer and the matrix. Nanocrystalline Ta–N layers (D(avg) = 45–55 nm) with dense and smooth surfaces were obtained at ≤950 °C, while grains grew and pores appeared on the surface of the Ta–N layers (D(avg) = 195–205 nm) at >950 °C. Consequently, the nanocrystalline Ta–N layer with gradient structure and desired thickness exhibited robust hardness and modulus of 26.89 and 247.64 GPa, respectively, which were considerably higher than those prepared by traditional gas/ion/liquid nitriding. The friction and wear test results showed that compared with pure Ta, the MPN-treated Ta matrix exhibited a shallower wear track, lower wear volume, and smaller superficial area, indicating that the Ta–N layer offered excellent surface protection for the matrix.

Surface nickel gradient tunes anionic redox activity to stabilize cobalt-free Li-rich cathodes

Constructing a gradient structure of transition metals is promising to improve the electrochemical performance of layered oxide cathodes. However, the nickel gradient spinel layer on the surface of layer Li-rich cathodes is barely successful. Herein, we present a refining strategy of reductive gas to induce a Ni-gradient spinel layer on the surface of Li1.2Mn0.6Ni0.2O2 (LRNMO). The formed gradient spinel layer stabilizes the coordination environment at the interface and reduces oxygen loss. Moreover, the Ni gradient further maintains the reversibility of the Mn3+/Mn4+ redox couple, while the multiple valence states of Mn ions in the gradient layer enhance the electrochemical kinetics. The LRNMO with Ni-gradient spinel layer achieves an initial coulomb efficiency reaching 86.1% and maintaining an energy density of 667.9 Wh kg−1 after 200 cycles at 1 C. The surface gradient strategy is conducive to maintaining structural stability and provides support for the continued development of Li-ion batteries.

Free vibration of functionally-graded piezoelectric semiconductor rectangular beam under thermal load

In this paper, the free vibration of a functionally-graded piezoelectric semiconductor (FGPS) rectangular beam under thermal load is studied within the framework of the theory of Timoshenko beam and the theory of piezoelectric semiconductor. It is assumed that the material properties in the functional gradient layer change smoothly. The multi-field coupling in the beam is deduced by introducing the first-order shear deformation theory in this paper, and the governing equations including motion equation, Gauss law and current continuity condition are obtained. The vibration of a simply supported FGPS rectangular beam is realized by solving the governing equations. In numerical examples, the natural frequencies of the FGPS rectangular beam under thermal load are analyzed through different perspectives. The results show that for different length scales, the natural frequency of the FGPS beam under thermal load is reduced by increasing the initial electron concentration in a certain range. The damping characteristics are insensitive to temperature change, and the damping characteristics are decreased by increasing length to thickness ratio and the thickness of the FGPS layer.

Effect of binder content and sintering time on the microstructure and mechanical properties of gradient cemented carbides with Ni binder

Replacement of Co by alternative Ni binder in gradient cemented carbide is an effective way to reduce the health concerns associated with Co powders. In the present work, gradient cemented carbides with different Ni contents and gradient sintering times were prepared by traditional powder metallurgy with a two-step sintering method. The microstructure of cemented carbide including the gradient layer formation was analyzed by XRD, SEM, EDS, TEM, and EBSD. The thickness of the gradient layer is almost proportional to the square root of sintering time, indicating that the gradient layer formation is a diffusion-controlled process. The atomic migration can be accelerated to form a thicker gradient layer with the increase of the binder content. The coherent interface of the Ti(C, N) core-rim structure for the gradient cemented carbides with Ni binder was revealed. With the increase in binder content, the average grain size of the WC phase is increased. The hardness and fracture toughness of the cemented carbides were also studied and analyzed according to the crack propagation behavior and the distribution of dislocation and stress indicated by KAM and GND. The variation of the hardness and the fracture toughness with the sintering time is mainly related to the density and the grain size of hard phases, while the change of the mechanical properties along with the Ni content probably results from the local dislocation density and the stress in the cemented carbides. The cemented carbide can obtain a good combination of hardness and fracture toughness with 10 wt% Ni gradient sintered for 2h.

Manufacturing and characterization of functionally gradient material from cemented carbide to diamond via filament-based material extrusion 3D printing

Functionally gradient material (FGM) fabricating via additive manufacturing draws great attention on alleviating the abrupt material discontinuity at the interface of different materials. Introducing gradient structure into polycrystalline diamond composites to produce diamond/cemented carbide FGM is an effective method to reduce the residual stress and enhance the bonding strength of diamond layer and cemented carbide substrate. However, achieving a smooth transition of material properties from cemented carbide to diamond is challenging. In this research, diamond/cemented carbide FGM with a well-controlled gradient was manufactured via filament-based material extrusion. Initially, green bodies of diamond/cemented carbide FGM were obtained by printing with customized composite filaments. Subsequently, thermal decomposition characteristic of the printing filament was analyzed by TGA, and the influence of different heating rates during the binder decomposition stage on the morphology and structure of the green bodies was investigated. After debinding, diamond/cemented carbide FGM without flaw was synthesized at 6.5 GPa and 1550℃. Subsequently, microstructure characterization was performed to investigate the distribution characteristics of the materials inside the diamond/cemented carbide FGM. A continuous transition from tungsten carbide to diamond was achieved inside the gradient layer. Furthermore, the stress state of diamond in different positions of the diamond/cemented carbide FGM was analyzed by Raman spectroscopy. It was found that all the residual stresses in the axial interface of the gradient layer were compressive stress, which can prevent occurrence of microcracks resulted from the tensile stresses formed in the interface. Finally, the impact tests reveal that gradient structure is conductive to improving the bond strength between PCD layer and cemented carbide substrate as the impact times before fracture of diamond/cemented carbide FGM has been increased by 15 %. The gradient structure design strategy, generated via the filament-based material extrusion technology, pioneers new ideas to the development of high-performance FGMs in mass production.

Virus ecology and 7-year temporal dynamics across a permafrost thaw gradient.

Soil microorganisms are pivotal in the global carbon cycle, but the viruses that affect them and their impact on ecosystems are less understood. In this study, we explored the diversity, dynamics, and ecology of soil viruses through 379 metagenomes collected annually from 2010 to 2017. These samples spanned the seasonally thawed active layer of a permafrost thaw gradient, which included palsa, bog, and fen habitats. We identified 5051 virus operational taxonomic units (vOTUs), doubling the known viruses for this site. These vOTUs were largely ephemeral within habitats, suggesting a turnover at the vOTU level from year to year. While the diversity varied by thaw stage and depth-related patterns were specific to each habitat, the virus communities did not significantly change over time. The abundance ratios of virus to host at the phylum level did not show consistent trends across the thaw gradient, depth, or time. To assess potential ecosystem impacts, we predicted hosts in silico and found viruses linked to microbial lineages involved in the carbon cycle, such as methanotrophy and methanogenesis. This included the identification of viruses of Candidatus Methanoflorens, a significant global methane contributor. We also detected a variety of potential auxiliary metabolic genes, including 24 carbon-degrading glycoside hydrolases, six of which are uniquely terrestrial. In conclusion, these long-term observations enhance our understanding of soil viruses in the context of climate-relevant processes and provide opportunities to explore their role in terrestrial carbon cycling.

Microstructures and tribological properties of MoS2/Mo2N multilayer gradient films deposited by reactive magnetron sputtering

In order to compare the microstructures and tribological properties of films, pure Mo2N, pure MoS2, 3-layer and 13-layer MoS2/Mo2N gradient films were deposited by reactive magnetron sputtering. The crystalline structure, surface and cross-section morphologies, 3D surface topography, binding energy, hardness and tribological properties of films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atom force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), nanoindenter, and wear tester, respectively. The results indicate that the preferred orientation of MoS2 in gradient films has changed. The surface and cross-section structures of gradient films become denser with increasing the number of gradient layers. Average surface roughness (Ra) of pure MoS2 film is the highest, and Ra of 13-layer film is the lowest. The binding energy of MoS2 in the composite layer of gradient film has changed. The hardness of gradient film is higher than that of MoS2 and lower than that of Mo2N. The wear resistance of gradient films is much better than that of pure MoS2, and this phenomenon is more obvious under high load conditions. The improvement in the wear resistance of gradient films is attributed to the increase of dense, hardness, H/E and H3/E2. In the initial stage of friction, the 3-layer gradient film can maintain low friction coefficient (≤0.15), which is attributed to the thick MoS2 surface layer. The wear resistance of 13-layer is much better than that of 3-layer gradient film, because it has higher hardness, higher H/E and H3/E2 than 3-layer gradient film.

The mass transport and electrochemical reaction in the cathode catalyst layer with ionomer/Pt gradient distribution

The mass transport and electrochemical reaction in the catalyst layer (CL) have a great impact on the performance of proton exchange membrane fuel cells (PEMFCs). In this study, a random algorithm is used to reconstruct the microstructure of the CL. The lattice Boltzmann method (LBM) is used to simulate the mass transport and electrochemical reaction in the CL. The CLs with ionomer/Pt gradient distribution are designed and then compared in terms of the oxygen concentration distribution, the number of reaction site and the reaction rate. The gradient type and number of gradient layers are also studied. It is found that the oxygen diffusion process and electrochemical reaction rate are significantly affected by the Pt/ionomer distribution. Compared with the uniform distribution CL, the reaction rate of CLs with ionomer/Pt gradient distribution can be improved by 14.4 % and 22.2 %, respectively.

Surface heterostructuring of 316L stainless steel manufactured by laser powder bed fusion and hot isostatic pressing

Metal additive manufacturing (AM), offering high freedom of design, has garnered attention as a cutting-edge manufacturing technology. Commonly, hot isostatic pressing (HIP), as post-processing, is utilized to remove undesirable defects in AM parts to obtain fully dense components. However, excessive heating during HIP can result in the deterioration of mechanical properties, limiting their potential for structural industry applications. Herein, we propose a new strategy to obtain an optimized gradient structure to achieve a substantial synergistic effect through ultrasonic nanocrystal surface modification (UNSM) on the HIP-processed AM substrate. The resulting microstructure shows an extended gradient layer reaching the center of the substrate with significant mechanical incompatibility between adjacent domains, showing an excellent combination of strength and ductility. Our study suggests that the optimized gradient structure with superior mechanical properties can be achieved by strategically exploiting HIP-induced effects, which are generally avoided in structural materials due to their deleterious effect on strength.