查看更多>>摘要：The microstructure evolution and mechanical behavior in directionally solidified Ni-rich Ni-Mn-Ga alloys with nominal compositions of Ni58Mn25Ga17 and Ni60Mn25Ga15 under compressive and tensile stresses have been investigated.The composition distribution shows the element Ni segregates in gamma phase,while elements Mn and Ga segregate in martensite phase.Furthermore,the microstructure orientation examined by electron backscatter diffraction(EBSD)indicates that beta phase has a preferred growth orientation of(001)A in Ni58Mn25Ga17 alloys,while gamma phase has a preferred growth orientation of(001)γ in Ni60Mn25Ga15 alloys.The fracture morphology suggests that the existence of ductile γ phase can reduce the crack propagation and promote fracture strain,particularly in the Ni60Mn25Ga15 alloys.Fi-nally,Schmid factor and deformation gradient tensor were calculated to well explain the crystallographic evolution during the detwinning under compressive and tensile stresses.The present findings not only elucidate the mechanism of y phase on the mechanical behavior of Ni-rich Ni-Mn-Ga alloys,but also shed light on the composition design of high temperature Ni-Mn-Ga shape memory alloys.
查看更多>>摘要：In the present work a new thermal conductivity model is developed for two-phase composite materials,which are consisted of a continuous matrix and dispersed 3D-particles separated from each other by the matrix as a function of grain size and volume ratio of the dispersed particles at different temperatures.The model is applied to reproduce experimental thermal conductivity values of cemented carbide systems WC-Co and WC-Ag.Good agreement was found between measured thermal conductivity data originating from both this work and recent literature and the calculated ones only using semi-empirical parameters for the interfacial thermal resistance(ITR)values at WC/Co,WC/Ag and WC/WC interfaces as a function of temperature.Additionally,the temperature and grain size dependence of the thermal conductivity for WC is established for the first time.The model works well for the case when the matrix(Ag)has a higher thermal conductivity compared to that of the WC particles and also for the case when the matrix(Co)has a lower thermal conductivity compared to that of the WC particles.The new model forms a physically sound basis for further development/materials design of cemented carbides and particle-reinforced composite materials.
查看更多>>摘要：Stainless steels have received wide attention as a substitute material for bipolar plates in high temper-ature proton exchange membrane fuel cell(HT-PEMFC).In the present work,the CrN,CrAlN and mul-tilayer CrN/CrAlN coatings were deposited on 316L SS to increase the corrosion resistance and decrease the interfacial contact resistance.The deposited coatings exhibited face centered cubic phase structure and it was verified from the X-ray diffraction pattern.X-ray photo electron spectroscopy results showed the formation of both CrN and CrAlN layers on 316L SS.CrN/CrAlN coating is more helpful in water management due to low surface roughness and high contact angle in the HT-PEMFC environment.The corrosion resistance behavior of all the samples were studied in 85％H3PO4 solution at 140℃purged with H2(HT-PEMFC anode)and O2(HT-PEMFC cathode)gases.The results showed that all the coatings considerably improved the performance of 316L SS and superior corrosion resistance was observed for CrN/CrAlN multilayer coating,whose protective efficiency was 98.12％and 96.14％in the two simulated HT-PEMFC environments.The results of electrochemical impedance spectroscopic studies demonstrated higher impedance for CrN/CrAlN coating.Surface morphological studies performed after corrosion stud-ies revealed that protection ability of CrN/CrAlN coating still remained acceptable.A very low interfacial contact resistance value of 6 mΩ cm2 at 140 N/cm2 was observed for CrN/CrAlN coating.Moreover,after corrosion studies,the interfacial contact resistance value of CrN/CrAlN coated 316L was much lower than that of CrN and CrAlN coatings due to the increased oxidation resistance.The maximum power density of about 0.93 W/cm2 at 2 A/cm2 and output voltage of 0.96 V was observed for CrN/CrAlN coating.
查看更多>>摘要：Basic thermal properties and mechanical properties are critical parameters for the structural magnesium alloys.Solute atoms and second phases can improve mechanical properties,but are deteriorating the heat dissipation performance.Through experimental determination of alloys,it is found that REMg12 phases have fewer negative impacts on thermal diffusivities than r1 phases.With the same intermetallic com-pound,the solute atom Zn have more negative influences on thermal diffusivities of Mg-Zn-La/Ce alloys than the content of second phases.In order to quantitatively evaluate thermal conductivities and further design Mg alloys with both high strength and high thermal conductivity,a calculated method is provided to describe the thermal diffusivity of alloys as a function of alloy composition and phase constitution A set of parameters for expression of thermal diffusivity of Mg-Zn-La/Ce alloys were obtained through assessing the experimental data.The thermal conductivities of Mg-Zn-La/Ce system were predicted and agreed well with experimental values with calculation error of 1.6％and standard error of±3.0 W/(m K)The calculation method considering thermal diffusivity resistivity improves the calculation accuracy and would be physically significant.
查看更多>>摘要：Recently,Coordination Polymers(CPs)have been widely utilized as energy storage materials for reversible Lithium-Ion Batteries(LIBs)benefiting from their tunable building blocks and adjusted electrochemical properties.However,the unsatisfied electrochemical behavior of CPs with poor conductivity and sluggish ion transport kinetics is still a bottle-neck for their large-scale energy storage applications in LIBs.Herein,we display the rational fabrication of a conductive Sn-based coordination polymer(Sn-DHTPA)via judi-ciously choosing suitable building units.The Sn-DHTPA is employed as anode for LIBs,exhibiting superior reversible storage capacity of 1142.6 mA h g-1 at 0.1 A g-1 after 100 cycles and impressive rate storage capability of 287.7 mA h g-1 at 20 A g-1.More importantly,a robust cycling performance of 205.5 mA h g-1 at an extra-high current density of 20 A g-1 are observed without remarkable capacity-fading up to 1000 cycles.The behavior superiority of Sn-DHTPA is related to its advanced architecture with abundant lithium storage sites,high electrical conductivity and rapid lithium transport.A series of ex-situ charac-terizations reveal that the impressive lithium storage capacity is contributed by the redox active sites of both the aromatic linker and metal center related to in-situ generated metallic nanoparticles dispersed in the skeleton.
查看更多>>摘要：From the perspective of high-temperature applications,materials with excellent high-temperature me-chanical properties are always desirable.The present work demonstrates that the binder-free nanopoly-crystalline WC ceramic with an average grain size of 103 nm obtained by high-pressure and high-temperature sintering exhibits excellent mechanical properties at both room temperature and high tem-perature up to 1000℃.Specifically,the binder-free nanopolycrystalline WC ceramic still maintains a considerably high Vicker hardness Hv of 23.4 GPa at 1000℃,which is only 22％lower than the room temperature Hv.This outstanding thermo-mechanical stability is superior to that of typical technical ce-ramics,e.g.SiC,Si3N4,Al2O3,etc.Nanocrystalline grains with many dislocations,numerous low-energy,highly stable Σ2 grain boundaries,and a relatively low thermal expansion coefficient,are responsible for the observed outstanding high-temperature mechanical properties.
查看更多>>摘要：Novel high-entropy perovskite-type(Ca0.2Sr0.2Ba0.2La0.2Pb0.2)TiO3(CSBLP)ceramics with cubic structure of Pm-3m space group were successful prepared by solid-state reaction method.Results of XRD,SEM-EDS,HRTEM confirmed a homogeneous distribution and equimolar arrangement of multicomponent cations on the A-site.The high-entropy CSBLP ceramics showed long-range structural order and short-range chemical disorder with widely dispersed nanoscale grains varying sizes of 4-6 nm in the microstructure.Because of increased configurational entropy,the CSBLP ceramic has an enhanced Seebeck coefficient(|S|=272 μV/K at 1073 K)and low thermal conductivity(κ=1.75 W/m·K at 1073 K)when annealed at 1300℃.This work demonstrates the possibility of effectively reducing thermal conductivity and improv-ing the performance of thermoelectric oxides through high-entropy composition design.
查看更多>>摘要：Supercapacitors are favored by researchers because of their high power density,especially with the ac-celeration of people's life rhythm.However,their energy density,especially from the point of view of the whole energy storage device,is far lower than that of commercial batteries.In this work,a kind of cus-tomizable full paper-based supercapacitor device with excellent self-healing ability is fabricated by simple and low-cost screen printing,electropolymerization and dip coating methods.The resultant separator-free supercapacitor device exhibits both ultrahigh gravimetric and areal specific energy(power)densities of 39 Wh kg-1(69 kW kg-1)and 692 μWh cm-2(236 mW cm-2),achieving excellent supercapacitor performance.Notably,the addition of vitrimers endows the whole device with outstanding self-healing properties,which is helpful for enhancing the adaptability of the device to the environment.In addition,this kind of paper-based device also displays good photothermal and electromagnetic shielding perfor-mances.These striking features make paper matrix composites attractive in the fields of supercapacitors,medical photothermal treatment and electromagnetic shielding.
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