查看更多>>摘要：Biodegradable magnesium(Mg)alloys have received much attention due to their biocompatibility and biodegradation.In this study,to uncover the effects of grain morphologies,including grain size and dis-tribution on mechanical and corrosion properties,biodegradable Mg-2.1Nd-0.2Zn-0.5Zr(wt.％)(denoted as JDBM)alloy mini-tubes for stent application with three typical microstructures were achieved success-fully by adjusting drawing parameters.Samples with the bimodal structure exhibit the highest strength-ductility balance attributed to the combined effects of fine grains and coarse grains,but show the fastest corrosion rate of about 1.00±0.136 mm/year mainly due to the formation of micro galvanic couples between coarse and fined grains.Samples with fine equiaxed grains show the lowest corrosion rate of about 0.17±0.059 mm/year,as well as uniform corrosion mode and mechanical properties of yield strength(YS)256±5.7 MPa,ultimate tensile strength(UTS)266±3.8 MPa,and elongation to failure(EL)13.5％±1.8％,attributed to the high-density grain boundaries.Samples with coarse equiaxed grains exhibit medium corrosion resistance and mechanical properties of about 175±4.8 MPa,221±4.0 MPa,and 21.53％±4.1％.Considering the mechanical and in vitro corrosion properties,biodegradable JDBM alloy implants are recommended to be composed of fine equiaxed grains,which can be used as mi-crostructural targets for fabrication and processing.
查看更多>>摘要：A new metastable dual-phase Fe59Cr13Ni18Al1o medium entropy alloy(MEA)with hierarchically heteroge-neous microstructure from micro-to nano-scale was designed in this work.Partially recrystallized FCC phase and lots of NiAl-rich B2 precipitates are obtained by annealing and aging treatment.The yield strength of the MEA at room temperature(298 K)and liquid nitrogen temperature(77 K)increased from～910 MPa and～1250 MPa in the annealed state,respectively,to～1145 MPa and～1520 MPa in the aged state,while the uniform elongation maintained more than 15％.The excellent mechanical properties of the MEA both at 298 and 77 K are attributed to the co-activation of multiple strengthening mech-anisms,including fine grain,dislocation,precipitation,transformation-induced plasticity,stacking faults,and nano-twins.
查看更多>>摘要：The advancement of all-solid-state Li metal batteries(ASSLMBs)faces a major challenge in the growth of lithium dendrites on the anode-electrolyte interface.In this study,we propose a dual-filler approach using poly(ethylene oxide)(PEO)-based solid polymer electrolytes(SPEs)that combine Li1.4Alo.4Ti1.6(PO4)3(LATP)ion-conductive particles with graphitic carbon nitride(g-C3N4)nanosheets.Analysis through sec-ond harmonic resonance enhanced electrostatic force microscopy and critical current density(CCD)tests reveal that the g-C3N4 additives form nano-capacitors at the SPE-lithium interface,effectively reducing sudden changes in current densities.The distribution of relaxation time constant(DRT)measurements confirms that the g-C3N4 filler suppresses uncontrolled Li dendrite growth,effectively mitigating battery aging caused by anode interfacial degradation.Furthermore,X-ray photoelectron spectroscopy(XPS)anal-ysis indicates that the nitrogen-containing organic groups in g-C3N4 are reduced to form a stable interfa-cial layer with lithium metal.As a result of these enhancements,the electrolyte demonstrates remarkable interfacial stability in Li/Li symmetrical cells at 0.65 mA/cm2 and delivers promising performance in as-sembled Li-LiFePO4 batteries,achieving a reversible capacity of 121.6 mAh/g at 1 C after 200 cycles.These findings highlight the potential of dual-filler PEO-based SPEs for promoting interfacial lithium-ion trans-port in all-solid-state Li metal batteries.
查看更多>>摘要：An extremely high-strength TiAl/Ni-based superalloy dissimilar joint was obtained using a designed Ni25Zr25Sn20Cu10Hf10Cr5Fe5 multi-principal element interlayer via contact reaction brazing.It was found that a joint mainly composed of eutectic structure of(Ni)ss,(Ni,Cr,Fe)ss,and(Cr,Ni,Fe,Mo)ss,as well as micro-nano precipitates of(Ti)ss and(Hf,Zr)ss,could be achieved through the interaction between the interlayer and the base metals.The joint exhibited a shear strength of 498 MPa when brazed at 1190℃ for 10 min,while the fracture occurred within the TiAl base metal,and the retention rate of high-temperature(HT)strength(650 ℃)was～100％.The strengthening mechanism of the brazed joint was systematically discussed by transmission electron microscopy(TEM).It was shown that high-density dis-locations existed in each phase of the seam as well as twinning and stacking faults existed in the micro-nano precipitates,caused by a mass of solute atoms,greatly strengthened the joint.At HTs,the dislocation strengthening effect weakened due to grain recovery and recrystallization,but the joint could be addi-tionally toughened by multi-cracking.Meanwhile,granular(Ti)ss dispersed through the seam and ductile reticular structure(Ni)ss toughened the joint via the mechanism of crack termination and bridging.The proposed method provides a new approach for high strength and heat resistance joining of TiAl/Ni-based superalloy in aeroengine components.
查看更多>>摘要：Solid state lithium-ion batteries(SLIBs)have been considered as one of the most promising sustainable next-generation technologies for energy storage.However,the poor interfacial compatibility and low ion conductivity of solid electrolytes still remain a major challenge for SLIBs.Herein,a free-standing flexible solid polymer LA-PAM-PEO electrolyte is constructed through the electrospinning technology featuring with high Li+conductivity(6.1 x 10-4 S cm-1),strong mechanical strength and high Li+migration num-ber(0.32),which breaks the restriction between ionic conductivity and mechanical strength in polymer solid electrolyte.The cross-linking between LA,PAM and PEO is verified to decrease the crystalline of PEO,thus increasing the Li+conductivity.Moreover,benefiting from the 3D network composed of in-terconnected nanofibers and the covalent bonds between LA,PAM and PEO,the mechanical strength of LA-PAM-PEO SPE was also effectively improved.The LA-PAM-PEO SPE also delivers a high electrochemi-cal window(4.95 V),and low interface resistance(243.8 Ω).As a result,the Li/Li symmetrical cell with the LA-PAM-PEO displayed outstanding stability after 1000 h with the uniform Li deposition on the in-terface of Li electrode,in sharp contrast to the PEO SPE.In addition,the Li/LA-PAM-PEO SPE/LFP displays a discharge capacity of 135 mA h g-1 after 1000 cycles at the rate of 1 C,with a capacity retention of 93.5％.The proposed LA-PAM-PEO SPE thus opens new possibilities for the fabrication and engineering of solid-state Li-ion batteries.
查看更多>>摘要：The development of artificial photosensitive synapses with high sensitivity and biomimetic properties that combine innovative concepts and neuromorphic architectures is crucial to achieving highly integrated and flexible intelligent visual systems.Recently,graphene heterostructure-based photosensitive synaptic transistors have been extensively studied for this purpose.However,compared to traditional transistors,vertical structure thin film transistors(VTFTs)with ultra-short channels and advantages,such as high integration,have yet to be investigated in photosensitive synapses.Here,we report an ultra-thin VTFT featuring a graphene/WxSex-1 van der Waals heterostructure that combines photonic and neuromorphic elements.We demonstrate a VTFT in which the channel layer is formed by covalently bonded WxSex-1 nanomaterials produced by introducing Se atoms on the surface of a tungsten metal thin film deposited via radio-frequency sputtering.This structure successfully simulated the main synaptic function,exhib-ited photosensitive synaptic responses to ultraviolet(λ=365 nm)light,and demonstrated highly reliable electrical performance.Furthermore,the incorporation of gold nanoparticles changed the photosensitive synaptic response properties of the graphene/WxSex-i heterostructure from excitatory to inhibitory,show-ing a responsivity of about～14 A W-1,which was attributed to the heterojunction interface resonant effects and efficient charge transfer induced by localized surface plasmons.This further enabled optical artificial synaptic applications while operating with low voltage spikes and low light intensity.This work provides a novel strategy for integrating and developing biological and nano-electronic systems.
查看更多>>摘要：The conventional selective template etching method to fabricate yolk-shell microwave absorbers is in-convenient and inefficient,so the thermally-driven contraction strategy was used to prepare asymmet-ric yolk-shell MnSe@C microsphere microwave absorbers via self-template directed transformation.The self-templated oriented transformation enables compositional customization and enhances the template utilization.The confinement effect of the carbon shell is crucial for realizing the thermally-driven con-traction strategy and contributes to the strong conduction loss to MnSe@C.On the other hand,the en-hanced polarization loss benefits from the abundant heterogeneous interfaces and defects in the asym-metric yolk-shell MnSe@C microspheres.The rich cavities in the yolk-shell structure not only facilitate optimal impedance matching,but also promote the enhancement of multiple reflection loss(RL).As a result,the asymmetric yolk-shell MnSe@C microspheres obtain excellent microwave absorption perfor-mance,the minimum RL(RLmin)and the maximum effective absorption bandwidth(EAB)reaching-54.4 dB and 5.1 GHz,respectively,at a thickness of 1.9 mm.The successful obtainment of the asymmetric yolk-shell MnSe@C microspheres paves the way for the convenient synthesis of the yolk-shell transition-metal selenides(TMSs)microwave absorbers.
查看更多>>摘要：Poly(p-phenylene-2,6-benzobisoxazole)(PBO)fiber and polytetrafluoroethylene(PTFE)resin have been widely acknowledged as excellent wave-transparent materials for future high-frequency applications due to their exceptional dielectric properties.However,the weak interfacial bonding between these two ma-terials hampers their full potential.In this study,we successfully addressed this limitation by enhanc-ing the surface roughness of PBO fibers and introducing active sites through the in-situ grafting of sil-ica nanowires.The added silica acted as an interfacial anchor on the PBO fiber surface,significantly improving the bonding force between PBO and PTFE.PBO/PTFE wave-transparent laminated composites were fabricated using hot compression molding.The results demonstrate that the PBO(treated with in-situ grown silica)/PTFE laminated composites exhibit superior interlaminar shear strength(ILSS),flexural strength,flexural modulus,and tensile modulus compared to the pristine PBO/PTFE laminated compos-ites.Specifically,these properties are found to be 58.6％,32.9％,138.1％,and 25.35％higher,respectively.Additionally,these composites demonstrate low dielectric constant and dielectric loss.Most notably,they achieve a wave transmittance of 91.45％at 10 GHz,indicating significant potential for wide-range applications in next-generation advanced military weapons,such as"lightweight/high-strength/wave-transparent"electromagnetic window materials,as well as civilian communication base stations.
查看更多>>摘要：The laser powder bed fusion(L-PBF)additively manufactured CoCrFeNi high-entropy alloy(HEA),with face-centered cubic(FCC)crystal structure,demonstrates better comprehensive mechanical properties in the building direction(BD).Loading quasi-static,dynamic fatigue,and dynamic separated Hopkinson press bar(SHPB)impact stress conditions along the BD of the L-PBF processed HEA exhibit intriguing mi-crostructural evolution characteristics.The L-PBF generates hierarchical dislocation grids containing nu-merous cell substructures within the HEA FCC grains,impeding dislocation motion during deformation and improving the strength.When subjected to dynamic fatigue loading,the dislocation grids restrict the mean free path of dislocations and thus trigger the activation of abundant stacking faults.Hence,nu-merous nanotwins form near the end of the fatigue life.Multiple twinning systems can also be activated under dynamic high-speed impact loading.Especially at a low temperature of 77 K,the stacking fault energy of the CoCrFeNi HEA decreases,resulting in increased activation of nanotwins,exhibiting excep-tional toughness and resistance to dynamic loads.Additional twin boundaries also impede dislocation movement for the strain hardening.These findings hold valuable implications for the study of additively manufactured HEA parts working in extreme environments.
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