查看更多>>摘要：In this work,bending fatigue behavior of thinner Zr61Ti2Cu25Al12 (ZT1) BMG beams with thicknesses of 500 μm and 100 μm were investigated with three-point bending (3PB),to evaluate the reliability and safety of this potentially material used in compliant mechanisms under cyclic bending load.Fatigue endurance limits (FELs) of ZT1 beams with thicknesses of 500 μm and 100 μm were determined to be 470 MPa,and ～0.3 of its tensile strength.Fatigue life and FEL of ZT1 beams in bending are substantially independent of the beam thickness,in the scale from 500 μm down to 100 μm.Fatigue cracks of all ZT1 beams initiated at the extrinsic microvoids,either indirectly derived from surface scratches during mechanical polishing or originated from as-cast process.However,fatigue crack propagation behavior is highly related to the magnitude of cyclic stress level.By interrupted fatigue tests,larger proportion about 60-70％ of fatigue life was spent on crack propagation under high stress level,while crack initiation occupied larger proportion about 80-85％ under low stress level.The medium stress level of about 590 MPa almost shared the crack-initiation life and crack-propagation life.In addition,there are two crack deflection mechanisms during cracks steady propagation stage.One mechanism is crack deflection along the interacted shear bands ahead of crack-tip,the other one is crack "jump" from one shear band to another shear band at a certain angle.These two mechanisms alternate dominate the crack propagation process,generating typical staircase-like crack propagation trajectory.Fatigue endurance limits of ZT1 beams in the form of either stress amplitude or strain amplitude are superior to traditional candidate materials in the field of compliant mechanisms,showing that the better reliability and larger deflection deformation can be achieved for flexible members made by ZT1 BMG even under cyclic loading.
查看更多>>摘要：Two alloys with different Ta and Al contents were applied to study the influence of Ta/Al ratio on the microstructural evolution and creep deformation under high temperature.The increase of Ta/Al ratio made the γ/γ'lattice misfit more negative and enhanced the volume fraction of γ'phase,which pro-duced cubic and small γ'phase in the initial microstructures.These initial tiny γ'phases impeded the dislocations movement and delayed the course of complete rafted γ'phase during the origination of creep deformation,which prolonged the time of the primary creep stage.Moreover,the increase of Ta/Al ratio and addition of Ru produced the denser and stable dislocation networks,the high APB energy and better solution strengthening,which hindered the climbing and sliding of dislocations,and restrained the formation of superdislocations in the γ'precipitate.The second creep stage was extended,and the min-imum creep rate was reduced.Hence,the increase of whole creep life of the alloy containing high Ta/Al ratio was attributed to the prolongation of the primary and second creep stages,and the low minimum creep rate.The appearance of the topological inversion phenomenon during the tertiary creep stage was the primary cause for the sudden increase of the creep strain rate of the alloy containing low Ta/Al ratio.However,the high creep strain rate of the alloy containing high Ta/Al ratio during the tertiary creep stage was related to the occurrence and extending of the cracks near the voids.Both alloys would lose efficacy within 20 h-30 h.
查看更多>>摘要：Efforts have been made to develop a promising anode material with a novel composition for sodium-ion batteries (SIBs).In this study,the sodium-ion storage mechanism of transition metal selenite that comprises transition metal cation coupled with two anions is studied.Amorphous cobalt selenite(CoSeO3)-carbon composite nanofibers containing numerous pores are synthesized via electrospinning process.Upon heat treatment of the electrospun nanofibers containing selenium,CoSe2 nanoclusters are formed.During the subsequent oxidation,CoSe2 transformed into amorphous CoSeO3 and some part of carbon was oxidized into CO2,leaving the pores inside the nanofiber.To unveil the electrochemical reaction mechanism,analytical methods including cyclic voltammetry,ex-situ X-ray photoelectron spec-troscopy,ex-situ transmission electron microscopy,and in-situ electrochemical impedance spectroscopy techniques were adopted.Based on the analyses,the following conversion reaction from the second cycle onward is suggested:CoO + xSeO2 + (1-x)Se + 4(x + 1)Na+ + 4(x + 1)e (←→) Co + (2x + 1)Na2O + Na2Se.Fur-thermore,the electrochemical properties of porous CoSeO3-carbon composite nanofibers are analyzed in detail.The anode material exhibited stable cycle stability up to 200 cycles at 0.5 A g-1 and high rate performance up to 5 Ag-1.
查看更多>>摘要：Sb2S3 is a promising candidate for the flexible solar cells or the top subcells in tandem solar cells due to its wide-bandgap,less toxic,acceptable cost and progressive power conversion efficiency (PCE).However,the poor quality and high trap states of Sb2S3 films limit the device performance further enhancement.Herein,we adopt a multidentate ionic liquid,tetramethylammonium hexafluorophosphate ([TMA][PF6])as a novel additive to address this issue.The octahedral[PF6]-contains six different oriented fluorine atoms with the lone pair electrons,which could coordinate with Sb atoms due to the multidentate anchor-ing.Thus,the high-quality Sb2S3 film with low trap states has been achieved.Moreover,the Fermi level of the Sb2S3 film has been upshifted,thereby showing an effective charge transfer.As a result,all photo-voltaic parameters of the optimized Sb2S3 devices are obviously enhanced,boosting the final PCE from 4.43 (control device) to 6.83 ％.Our study about the multidentate anchoring is manifested to be an effective method to enhance the Sb2S3 device performance.
查看更多>>摘要：The discovery of band convergence has opened an effective avenue for significantly enhancing thermo-electric performance of SnTe,while alloying CdTe in SnTe is evidenced efficient for improving the valley degeneracy.However,the thermoelectric transport properties are limited due to the low solubility of CdTe in SnTe (～3％).Inspired by the improvement of dimensionless figure of merit zT in Cu or Se-doped SnTe,investigating the effect of Cu2Se on the electronic and phonon transport properties of SnTe-CdTe alloys is highly desired.Traditionally,improving the quality factor can trigger an increase of the potential of a compound for higher zT,which is of importance for design of thermoelectric materials.Here,alloyed 3％ Cu2Se in SnTe-3％CdTe system enables an increased peak zT,which is attributed by the optimization of electronic performance (～21 μW cm-1 K-2 at 800 K),as well as the decreased lattice thermal conductivity owing to the enhanced mass and strain fluctuations.More importantly,alloying Cu2Se not only improves the quality factor from ～0.25 to ～0.45,resulting in a higher maximum potential zT,but also effectively preserves the Fermi energy in a relative optimized level.The current findings demonstrate the role of Cu2Se for manipulating thermoelectrics in SnTe.
查看更多>>摘要：Transition-metal based hybrids with excellent stability and activity are favorable candidates for hydrogen evolution reaction (HER).The development of typical Co3S4 has recently received considerable atten-tion due to the multiple valences of the spinel-structured compound.However,the in-depth effect of the dopants on the HER performance of Co3S4 has not been systematically clarified.Here,we report a sequential synthesis of a spinel-structured cobalt phosphosulfate nanoneedle arrays grown on carbon cloth (namely,P-Co3S4/CC).Results indicate that P-Co3S4/CC exhibits high electrocatalytic performance for HER with a low overpotential of 65 mV to drive10 mA cm-2,a small Tafel slope of 76.6 mV per decade,and great long-term stability for 25 h at various current densities in alkaline electrolyte.The first-principle calculation result reveals that the phosphorous doping work at Co3S4 enhances the HER performance sig-nificantly because the tetrahedral Co2+ active sites nearest the P atoms more easily weaken the H-O bond to form intermediates.The experiment result characterization and theoretical calculations further show that the introduction of P atom not only offers more active sites but also improves the electrical con-ductivity in an alkaline electrolyte solution.Consequently,the identification of active species provides feasible guidance for the further design of high-performance spinel-structured catalysts.
查看更多>>摘要：A laser texturing technique herein can endow bare aluminum alloy surface with regular dimple-pattern array and thus generates a case hardening.After STA treatment,these laser-textured samples become superhydrophobic.The surface wettability of the laser-textured samples can be regulated by control-ling the dimple-pattern dimensions during the laser processing.It is noteworthy that a fluorescence method is utilized to record the zones on the superhydrophobic surface penetrated by small enough water molecules.Compared with a general method of the Cassie-Baxter theoretical calculation,this fluorescence method intuitively exhibits the air trapping ability of the superhydrophobic surface.Fur-thermore,the laser-textured superhydrophobic samples have a notable hysteresis phenomenon at the initial period of UMT friction because the air cushion trapped within superhydrophobic samples have strong repellency against water droplets on the hydrophilic steel ball.Additionally,such samples display strong mechanical stability in comparison with bare aluminum alloy because of the presence of case hardening on the surface of the laser patterns.The research results above provide a valuable reference for designing a surface with different wettability,which may inspire practical applications in the fields of fluid transport,droplet manipulation,water harvesting and microfluidic devices.
查看更多>>摘要：Among the various anodes,Li3VO4 is a potential intercalation kind anode used in lithium-ion batteries(LIBs) that exhibits safer discharge voltage and higher capacity than graphite,a lower voltage plateau than Li4Ti5O12,and smaller volume difference in the Li+ intercalation/deintercalation process than met-als and alloys.However,the comparatively low electronic conductivity,low initial coulombic efficiency(ICE) and serious capacity decay make the Li3VO4 anode unviable when it comes to practical implemen-tation.Therefore,this paper reviews the research progress of Li3VO4 in recent years,mainly including the strategies of developing different synthesis methods to construct unique morphology,through coating,compositing or elemental doping to increase the ICE,electronic conductivity and the cycle constancy.Moreover,the application of Li3VO4 anode materials in other energy storage systems is summarized.Lastly,the development prospect and challenge of Li3VO4 anodes are discussed.
查看更多>>摘要：Over recent years,eutectic high-entropy alloys (EHEAs) have intrigued substantial research enthusiasms due to their good castability as well as balanced strength-ductility synergy.In this study,a bulk cast Al19.25Co18.86Fe18.36Ni43.53 EHEA is developed with fine in-situ lamellar eutectics.The eutectics comprise alternating ordered face-centered-cubic (L12) and ordered body-centered-cubic (B2) phases with semi-coherent interfaces.The resulting microstructure resembles that of most reported as-cast EHEAs,but the B2 lamellae are devoid of nano-precipitates because of the Cr-element removal in current tailored eutectic composition.Surprisingly,the B2 lamellae still feature much higher deformation resistance than the L12 lamellae,so that less lattice defects are detected in the B2 lamellae until the fracture.More interestingly,in the L12 lamellae we identify a dynamic microstructure refinement that correlates to extraordinary strain hardening in tension.The precipitate-free EHEA consequently shows excellent tensile ductility of～10 ％ and high ultimate strength up to ～956 MPa.
查看更多>>摘要：The phase transformation and microstructure in Ti-22Al-25Nb alloy are extremely complex.In this work,the morphology evolution of the O phase during the heating and cooling process was investigated by electron backscatter diffraction (EBSD) and first-principles calculations.The results show that the O→α2 phase transformation process during the heating process is as follows:spheroidization of the O phase occurs first,then the α2 phase nucleates in the spheroidized O phase,grows and replaces the O phase,completing the O→α2 phase transformation.In the meanwhile,the diffusion of Nb from Nb-poor O to Nb-rich B2 phases is a back-diffusion process.According to first-principles calculations,the driving force of the O→α2 phase transformation is the difference in the free energies of formation for the two phases(0.09eV/atom).When the Nb content is greater than 15.625 ％,the lattice distortion of the α2 phase sharply increases,and the distortion energy drives the back-diffusion of Nb.During the cooling process,the α2→O phase transformation is difficult and slow due to the difficult diffusion of Nb from the B2 to α2 phases.When holding for 60 min at 960 ℃,the coarse α2 phase gradually transforms to the O phase from the margin to the inside,forming a dispersed mixed structure of the O and α2 phases.During the B2→O transformation,the nucleation of the O phase induces a high stress region,in the range of approximately 200 nm.
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