查看更多>>摘要：The spatial arrangement,distribution and morphology of Fe-bearing intermetallics in AA6082 alloys de-pends on the manufacturing process of the alloy and thus influences the macroscopic properties.Here,the microstructure of a near industrial scale casting AA6082 Al alloy fabricated by:(a)direct chill cast-ing,(b)Al-5Ti-1B grain refiner addition and(c)intensive melt shearing has been investigated by three-dimensional visualization using SEM-based serial ultramicrotomy tomography.The formation sequence of phases in AA6082 alloys is generally categorized into four stages:formation of α-Al grains,Fe-bearing intermetallics,Mg2Si phase,and eutectic rosettes.Results of three-dimensional visualization of the mi-crostructure indicated that TiB2 particles not only could nucleate Fe-bearing β-intermetallics,but also could provide substrate for the formation of Fe-bearing α-intermetallics and Mg2Si.A further deep anal-ysis reveals that the essential condition for the formation of secondary phases such as Fe-bearing in-termetallics and Mg2Si phase is the build-up of a supersaturated solute front at the α-Al solid-liquid interface irrespective of the specific nucleation site.In addition,the results indicate that grain refinement processing causes the severe interconnectivity of Fe-bearing α-intermetallics.However,the intensive melt shearing is a better manufacturing process because the intermetallics are more evenly distributed and re-fined than with the addition of the grain refiner,thereby improving the properties of the alloy.
查看更多>>摘要：Development of a low-cost and durable bifunctional electrocatalyst with high catalytic activity by hy-bridizing rare earth metal and non-noble metal is of utmost significance.Herein,a bifunctional electrocat-alyst consisting of MoO2 and CeOx heterostructure is synthesized via interfacial engineering.Particularly,due to its unique hetero-interface with abundant oxygen vacancies,the MoO2-CeOx/NF is able to exhibit outstanding hydrogen evolution reaction(HER)performance with an overpotential of 26 mV at 10 mA cm-2,and a preferable oxygen evolution reaction(OER)overpotential of 272 mV at 100 mA cm-2 in 1 M KOH.The recorded HER and OER overpotentials of MoO2-CeOx/NF are clearly smaller than those of Pt/C(HER overpotential of 27 mV)and RuO2(OER overpotential of 393 mV)at the same current density.More importantly,MoO2-CeOx/NF can also exhibit good HER activity with an overpotential of 50 mV at 10 mA cm-2 in acidic media.Thus,it is expected that this work can offer a new approach in the realization of high-catalytic alkaline overall water splitting and acidic HER performance through the rational design of rare-earth metal and non-noble metal heterostructure.
Min FengChengyang JiangMinghui ChenShenglong Zhu...
139-149页
查看更多>>摘要：Glass-ceramics are usually obtained through controlled crystallization.In this work,we propose a new strategy to add an appropriate amount of oxide particles to the parent glass to improve the performance of glass-ceramics.Different amounts of Al2O3 or/and CeO2 particles were added into a SiO2-Al203-ZnO-CaO-ZrO2-TiO2 based glass,and crystallization behavior,fracture strength,and thermal shock behavior were systematically evaluated.The results indicate that with the addition of Al2O3 or/and CeO2 particles of moderate amount,the unfavorable needle-like ZrSiO4,Zn2SiO4,and CaTiSiO5 crystals were largely in-hibited when annealed at 900℃.Accordingly,fracture strength is maintained high after heating at high temperatures.The thermal shock resistance is also enhanced drastically.The additive Al2O3 is thermo-dynamically favorable to react with the glass,forming particulate ZnAl2O4 instead of precipitating the needle-like crystals of Zn2SiO4 and CaTiSiO5;while CeO2 will combine with ZrO2 to form a solid solu-tion and promote the precipitation of primary crystal CaZrTi2O7 that will not transform to ZrSiO4 with prolonging thermal exposure.
查看更多>>摘要：Thermoelectric generators(TEGs)have received increasing attention due to their potential to harvest low-grade heat energy(＜100℃)and provide power for the Internet of Things(IoT)and wearable elec-tronic devices.Herein,a wood-based ordered framework is used to fabricate carbon nanotube/poly(3,4-ethylenedioxythiophene)(CNT/PEDOT)wood aerogel for TEG.The prepared CNT/PEDOT wood aerogel with an anisotropic structure exhibits a low thermal conductivity of 0.17 W m-1 K-1 and is advantageous to develop a sufficient temperature gradient.Meanwhile,CNT/PEDOT composites effectively decouple the relationship between the Seebeck coefficient and electrical conductivity by energy filtering effect to en-hance thermoelectric(TE)output properties.The vertical TEG assembled by the CNT/PEDOT wood aero-gels reveals an output power of 1.5 μW and a mass-specific power of 15.48 μW g-1 at a temperature difference of 39.4 K.Moreover,the layered structure renders high compressibility and fatigue resistance.The anisotropic structure,high mechanical performance,and rapid thermoelectric response,enabling the TEG based on CNT/PEDOT wood aerogel offer opportunities for continuous power supply to low-power electronic devices.
查看更多>>摘要：Aqueous multivalent-metal-ion intercalation chemistries hold genuine promise to develop safe and pow-erful microbatteries for potential use in many miniaturized electronics.However,their development is beset by state-of-the-art electrode materials having practical capacities far below their theoretical val-ues.Here we demonstrate that high compatibility between layered transition-metal oxide hosts and hydrated cation guests substantially boost their multi-electron-redox reactions to offer higher capaci-ties and rate capability,based on typical bipolar vanadium oxides preintercalated with hydrated cations(MxV2O5).When seamlessly integrated on Au current microcollectors with a three-dimensional bicon-tinuous nanoporous architecture that offers high pathways of electron transfer and ion transport,the constituent ZnxV2O5 exhibits specific capacity of as high as～527 mAh g-1 at 5 mV s-1 and re-tains～300 mAh g-1 at 200 mV s-1 in 1 M ZnSO4 aqueous electrolyte,outperforming the MxV2O5(M = Li,Na,K,Mg).This allows aqueous rechargeable zinc-ion microbatteries constructed with sym-metric nanoporous ZnxV2O5/Au interdigital microelectrodes as anode and cathode to show high-density energy of～358 mWh cm-3(a value that is forty-fold higher than that of 4 V/500 μAh Li thin film bat-tery)at high levels of power delivery.
查看更多>>摘要：Dual face-centered cubic(FCC)CoCrCu1.2FeNi semi-solid billets were prepared by semisolid isothermal treatment of wrought high entropy alloy(HEA)(SSITWH)method,and the microstructure evolution in the whole process of billets preparation was systematically investigated by optical microscopy,scanning electron microscopy,electron backscatter diffraction and transmission electron microscopy.The hot de-formed feedstock was mainly composed of deformation structure with preferred orientations and a small number of dynamically recrystallized grains of FCC1 phase.In the semi-solid stage,the effect of temper-ature and soaking time on semi-solid microstructure was studied in the range of 1130-1250℃and 5-120 min.The semi-solid microstructure was evaluated quantitatively.The average grain size and average shape factor increased with the increase of soaking time and isothermal temperature.After isothermal heat treatment,the segregation of Cu in FCC1 phase reduced to a certain extent.Semi-solid coarsening kinetics analysis showed that the alloy had low coarsening coefficients.When the temperatures were 1130℃,1175℃,1200℃,1225℃and 1250℃,the coarsening coefficients were 1.08 μm3/s,5.95 μm3/s,6.17 μm3/s,17.58 μm3/s,38.67 μm3/s,respectively.A coarsening kinetic equation describing solid grain growth was established.During heating up,FCC1 and FCC2 phase recrystallized successively.At higher temperature,FCC2 phase was spheroidized to a certain extent.When temperature was raised to semi-solid range,the grains of FCC2 phase coalesced,grew up and spheroidized and the preferred orientations basically disappeared.The types of semi-solid melting characteristics of HEAs were summarized in this paper.The semi-solid melting behavior of alloys is essentially affected by phase structure,phase number,phase volume content and composition.
查看更多>>摘要：The study on temperature dependence of exchange bias field and coercivity is crucial to solving the writ-ing/reading dilemma in magnetic recording.Motivated by recent experimental findings,a complete switch between exchange bias field and coercivity with temperature is proposed,and the performance,charac-terized by average switching temperature(Ts)and switching temperature width(ΔTw),controlled by antiferromagnetic anisotropy(KAF)and exchange coupling(JAF)constants is studied based on a Monte-Carlo simulation.The results show that a linear relationship between Ts and KAF is established when KAF is above a critical value,while Ts is weakly influenced by JAF.On the contrary,ΔTw is insensi-tive to KAF,while strongly depends on JAF.Besides overcoming thermal energy,the increase of KAF for a small JAF guarantees the completely frozen states in the antiferromagnetic layers during magnetizing at higher temperature,below which the exchange bias field exists with a negligible coercivity.Otherwise,for a large JAF,the uncompensated antiferromagnetic magnetization behavior during the ferromagnetic magnetization reversal becomes complicated,and the switching process in the low temperature range depends on the irreversibility of uncompensated antiferromagnetic magnetization reversal during mag-netizing,while in the high temperature range mainly influenced by the field-cooling process,resulting in a large ΔTw.This work provides an opportunity to control/optimize the performance of the temperature-induced switch between unidirectional and uniaxial symmetries through precisely tuning KAF and/or JAF to meet different application demands in the next generation information technology.
查看更多>>摘要：Toughness and strength are important material parameters in practical structural applications.However,it remains a great challenge to achieve high toughness and high strength simultaneously for most mate-rials.Here,we report a folded graphene(FG)reinforced copper(Cu)nanocomposite that overcomes the long-standing conflicts between toughness and strength.Intensive molecular dynamics simulations show that the 10％pre-strain-induced four-wave-patterned FG(1.09 wt％)reinforced Cu nanocomposite exhibits simultaneous enhancement in toughness(～13.59 J/m2),ductility(～32.38％),and strength(～9.52 GPa),corresponding to 38.53％,58.88％,and 2.26％increase,respectively when compared with its counterpart reinforced by pristine graphene(PG).More importantly,the mechanical properties of FG/Cu nanocom-posites can be effectively tuned by changing the pre-compressive strain,wave number,and peak number of FG.The toughening and strengthening mechanisms are applicable to other metal materials reinforced by other 2D nanomaterials,opening up a new avenue for developing tough and strong metal nanocom-posites.
查看更多>>摘要：SnSe,possessing strong lattice anharmonicity and structural anisotropy,has attracted massive attention in thermoelectric conversion.Herein,we demonstrate that simultaneously optimized electrical and ther-mal transport properties are achieved in SnS2-alloyed SnSe polycrystalline materials,which were fabri-cated via sintering the mixture of solution-synthesized SnSe microplates and SnS2 nanoplates.Resulting from the increased carrier concentration,p-type(SnSe)1-x(SnS2)x(x = 0.5％,1％)samples obtain much-improved power factor between 300 K and 373 K,e.g.0.72 mW m-1 K-2 at 300 K for(SnSe)0.99(SnS2)0.01,which is enhanced by 53％compared to that of SnSe.Additionally,the existing point defects and planar defects effectively strengthen phonon scattering,thus reducing the lattice thermal conductivity,for ex-ample,0.47 W m-1 K-1 at 773 K for the x = 0.02 sample.Eventually,a maximum zT of 0.80 at 823 K and an average zT of 0.52 over 300-823 K are obtained in the(SnSe)0.99(SnS2)0.01 sample,which are increased by 33％and 45％compared to those of SnSe,respectively.This study demonstrates a secondary phase alloying strategy to synergistically optimize the electrical and thermal properties of polycrystalline SnSe.
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