Guoyin ChenWeiming WangXin LuInnocent Tendo Mugaanire...
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查看更多>>摘要：Reduced graphene oxide(rGO)-based fibers with high electrochemical performance have recently showed great potential in the field of flexible energy storage devices.However,they still suffer from low ca-pacitance due to the severe stacking of graphene sheets.Hybrids with nanofillers are an efficient way to improve the electrochemical performance of rGO fibers.Nevertheless,controlling the distribution of nanoparticles in the matrix is still an enormous challenge due to the strong attraction among these nanoparticles which results into agglomeration.Here,we continually prepared rGO hybrid fibers via non-liquid-crystal spinning,accompanied by chemical reduction.Manganic oxide(MnOx)nanoparticles re-mained well-dispersed in GO dispersion during the continuous spinning of rGO/MnOx hybrid fibers.Re-sults showed that rGO/MnOx-20 hybrid fibers possessed the best capacitance of 123.3 F g-1(87.6 F cm-3)and 97.1 F g-1(68.9 F cm-3)at the current density of 0.2 A g-1,and 0.5 A g-1 respectively.Furthermore,a fiber-shaped all-solid-state supercapacitor assembly from the optimized hybrid fibers demonstrated an energy density of 2.67 mWh cm-3(3.76 mWh g-1)at the power density of 24.76 mWh cm-3(34.89 mWh g-1).These fiber-based devices show great potential for application in the fields of wearable electronics and energy storage devices.
查看更多>>摘要：CrMnFeCoNi high-entropy alloys(HEAs)exhibit an excellent combination of tensile strength and ductility at cryogenic temperatures.This study led to the introduction of a new method for the development of high-performance CrMnFeCoNi HEAs at cryogenic temperatures by jointly utilizing additive manufactur-ing(AM)and the addition of interstitial atoms.The interstitial oxygen present in the powder feedstock was transformed into beneficial nano-sized oxides during AM processing.The HEA nanocomposite fab-ricated using laser powder bed fusion(L-PBF)not only contains heterogeneous grains and substructures but also a high number density of nano-sized oxides.The tensile results revealed that the L-PBF HEA nanocomposite has superior yield strengths of 0.77 GPa and 1.15 GPa,and tensile strengths of 0.92 GPa and 1.45 GPa at 298 K and 77 K,respectively.In addition,the Charpy impact energies of the samples tested at 298 K and 77 K were measured as 176.2 J and 103.7 J,respectively.These results indicate that the L-PBF HEA nanocomposite successfully overcomes the well-known strength-toughness trade-off.The tensile deformation microstructure contained a relatively large number of deformation twins(DTs)at cryogenic temperature,a possible consequence of the decrease in the stacking fault energy with decreas-ing temperature.On the other hand,cracks were found to propagate along the grain boundaries at room temperature,whereas a transgranular crack was observed at cryogenic temperature in the specimens fractured as a result of the Charpy impact.
查看更多>>摘要：The effects of cryogenic thermal cycling on deformation behaviour and structural variation of{[(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4}99.9Cu0.1 bulk metallic glass(BMG)were studied and compared with Cu-free[(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 BMG.After thermal-cycled treatment between 393 K and cryogenic temperature,the{[(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4}99.9Cu0.1 BMG obtained a plastic strain of 7.4％combined with a high yield strength of 4350 MPa.The excellent soft magnetic properties were maintained after CTC treatment.The minor addition of Cu element results in an initial nano-sized heterogeneity in the matrix,which facilitates the rejuvenation process during thermal cycling,and brings to a low optimal thermal temperature of 393 K,making the{[(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4}99.9Cu0.1 BMG more attractive in industrial application.During thermal cycling,the formation of more soft regions leads to the increase of structural heterogeneities,which is beneficial to the initiation of shear transition zones and the for-mation of multiple shear bands,and thus results in the enhancement of plasticity.This study links the subtle variation of specific structure with macroscopic mechanical properties,and provides a new insight of composition selection for cryogenic thermal cycling treatment.
查看更多>>摘要：In this work,the high temperature friction mechanism of the tetrahedral amorphous carbon(ta-C)film was elucidated.The multilayer ta-C film with alternating hard and soft sub-layers exhibited a low fric-tion coefficient of 0.14 at 400℃before a sudden failure occurred at 4600 cycles.The wear failure was at-tributed to the gradual consumption of the ta-C film at the contact region.The design of a hard or soft top layer effectively regulated the high temperature friction properties of the multilayer ta-C.The addition of a hard top layer contributed to a low friction coefficient(0.11)and a minor wear rate(4.0×10-7 mm3/(N m)),while a soft top layer deteriorated the lubrication effect.It was proposed that the passivation of dan-gling bonds at the sliding interface dominated the low-friction mechanism of the ta-C film at high tem-perature,while the friction induced graphitization and the formation of sp2-rich carbonaceous transfer layer triggered C-C inter-film bonding,resulting in serious adhesion force and lubrication failure.More-over,the multilayer ta-C film with hard top layer obtained excellent friction performance within 500℃,while the high temperature induced oxidation and volatilization of carbon atoms led to the wear failure at 600℃.
查看更多>>摘要：The present study addressed the change in the microstructure of Al-2.5 wt％Fe binary alloy produced using laser powder bed fusion(L-PBF)technique by thermal exposure at 300℃,and the associated mechanical and thermal properties were systematically examined as well.Multi-semi-cylindrical pat-terns corresponding to melt pools in the microstructure were macroscopically observed for the as-manufactured sample.No change in the melt-pool morphology was observed after thermal exposure for 1000 h.Inside the melt pools,a large number of the nanoscale metastable Al6Fe phase particles were uniformly distributed inside columnar grains of the α-Al matrix containing concentrated solute Fe in su-persaturation.The sequential formation and coarsening of stable θ-Al13Fe4 phases were observed upon exposure to a 300℃environment,but a considerable amount of nano-sized metastable Al6Fe phases re-mained even after 1000 h.Furthermore,the thermal exposure continuously reduced the concentration of solute Fe atoms in the α-Al matrix.No significant grain growth was found in α-Al matrix after 1000 h owing to the pinning effect of the dispersed fine particles on grain boundary migration.These results demonstrate a sluggish change in microstructural morphologies of the Al-2.5 wt％Fe alloy.The quan-tified microstructural parameters addressed dominant strengthening contributions by the solid solution of Fe element and Orowan strengthening mechanism by fine Al-Fe intermetallics in the L-PBF-produced alloy.The high strength level was sustained even after being exposed to 300℃for long periods.The superior balance of mechanical properties and thermal conductivity can be achieved in the experimental alloys by taking advantage of the various microstructural parameters related to the Al-Fe intermetallic phases and α-Al matrix.
查看更多>>摘要：Ultrafast heating(UFH)at the rates of 10-300℃/s was employed as a new strategy to anneal a cold-rolled 7wt％Mn steel,followed by the immediate cooling.Severely deformed strain-induced martensite and lightly-deformed thermal martensite,both had been already enriched with C and Mn before,trans-formed to fine and coarse austenite grains during the UFH,leading to the bimodal size distribution.Com-pared with the long intercritical annealing(1A)process,the UFH processes produced larger fraction of RA grains(up to 37％)with a high density of dislocation,leading to the significant increase in yield strength by 270 MPa and the product of strength and elongation up to 55 GPa％due to the enormous work hard-ening capacity.Such a significant strengthening is first attributed to high density dislocations preserved after UFH and then to the microstructural refinement and the precipitation strengthening;whilst the sus-tainable work hardening is attributed to the successive TRIP effect during deformation,resulting from the large fraction of RA instantly formed with the bimodal size distribution during UFH.Moreover,the results on the microstructural characterization,thermodynamics calculation on the reverse transformation tem-perature and the kinetic simulations on the reverse transformation all suggest that the austenitization during UFH is displacive and involves the diffusion and partition of C.Therefore,we propose that it is a bainite-like transformation.
查看更多>>摘要：Development of bone fixation devices with excellent corrosion resistance,antibacterial ability,and os-teogenic activity is critical for promoting fracture healing.In this study,Zn-incorporated nanopore(NP)layers were prepared on the NiTi alloy through anodization and hydrothermal treatment.Results show that Zn can be evenly incorporated into the NP layers in the form of ZnTiO3.The Zn-incorporated sam-ples exhibit good corrosion resistance and significantly reduce Ni2+release.Meanwhile,the samples can continuously release Zn2+,which is responsible for excellent long-term antibacterial ability.Furthermore,the synergetic effect of Zn2+release and nanoporous structure of the NP layers endues the NiTi alloy excellent osteogenic activity,as verified by upregulated alkaline phosphatase activity,secretion of type Ⅰ collagen,and extracellular matrix mineralization.Therefore,Zn-incorporated Ni-Ti-O NP layers have great potential as biomedical coatings of NiTi-based implant materials.
查看更多>>摘要：The emergence of MAX borides as well as MAB phases attracted great attention because of the renewable developments of ternary ceramics and offering great opportunities in potential applications.However,the number of borides remains limited,and further fundamental descriptions and detailed investigations on various properties are still lacking.In this report,we employ an integrated computational scheme that combines density functional theory with the evolutional algorithm to search for the favorable structures of P-and S-glued ternary borides terminated by Nb metal.We discover that the structures of 212-type,as e.g.Nb2PB2 and Nb2SB2,belong to the P6m2 space group,while those of 211-type,as e.g.Nb2PB and Nb2SB,prefer to crystallize in the P63/mmc space group,and the corresponding carbides Nb2PC and Nb2SC are also considered for the sake of completeness and comparative analsys.The predicted Nb2PB2,Nb2PB,Nb2SB,Nb2PC and Nb2SC are energetically stable,as revealed by the negative formation energies and by the proposed reaction paths with respect to the most competing phases,as well as dynamically stable,as suggested by the non-imaginary phonon spectra.The thermal conductivities of the six materials show unusual behaviors,particularly for the acoustic and optical contributions,and are accompanied by a strong anisotropy.Most importantly,Nb2PB2 is found to be an excellent thermal conductor with a total thermal conductivity of～65 W/(m K),while Nb2SC is found to be an ultra-low thermal conductor,with a total thermal conductivity of～5 W/(m K).These values are clearly outside the currently reported range of thermal conductivities,which makes Nb2PB2 and Nb2SC extremely interesting for fundamental research as well as prospective applications with the aid of artificial tunings on the almost independent MB block and the A layer.The discovery of these novel materials is expected to contribute substantially to the rapid development of ternary ceramics and to accelerate attempts in the applicability of MAX phases for heat conduction.
查看更多>>摘要：Via traditional wire drawing,the medium carbon ferrite-pearlite(MCFP)steel wires can achieve the ultra-high strength beyond 4 GPa normally for high-carbon pearlitic steel wires,but have a 30-60％lower pro-duction cost.The microstructural evolution and mechanical properties of medium carbon ferrite-pearlite steel wires have been investigated by means of scanning electron microscopy,transmission electron mi-croscopy and tensile testing.The tensile strength of medium carbon ferrite-pearlite steel wires increases from 750 MPa up to 4120 MPa when the drawing strain increases up to ε=6.4,which represents the highest strength reported so far-to our knowledge for a carbon steel with such low carbon content.At low and medium strains(ε≤1.95),the proeutectoid ferrite forms dense dislocation walls(DDWs)via dislocation activities,including sliding,accumulation,interaction,and tangling.With the drawing strain increase,the reorientation of DDWs to the drawing direction forms the coarse proeutectoid ferrite lamel-lae.Finally,the proeutectoid ferrite deformed to high strains is characterized by a lamellar morphology and the average lamellar spacing of proeutectoid ferrite is about 55 nm at ε=6.4.The interlamellar spacing of pearlite and thickness of cementite decreases with the drawing strain increases.The disloca-tion density in ferrite lamellae increases with the drawing strain increases,and the dislocation density in ferrite lamellae is 7.8×1015 m-2 at ε=4.19.A higher dislocation density of 3.1 x 1016 m-2 can be obtained at ε=6.4 by means of extrapolation and TEM investigations.The stress contributions of proeutectoid ferrite and pearlite to the flow stress are estimated based on quantified structural parame-ters.Based on the assumption that the stress contributions from different strengthening mechanisms are linearly additive and the general rule of mixtures,a good agreement between the measured and esti-mated flow stresses has been found in a large range of flow stress.The good application of the general rule of mixture to the medium carbon ferrite-pearlite steel wires indicates the importance of quantitative characterization of microstructural evolution and parameters with the strain.
查看更多>>摘要：The competitive effect of microstructural features including primary α(αp),secondary α(αs),grain boundary α(αGB)and β grain size on mechanical properties of a near β Ti alloy were studied with two heat treatment processes.The relative effect of β grain size and STA(solution treatment and ageing)pro-cessing parameters on mechanical properties were quantitatively explored by the application of Taguchi method.These results were further explained via correlating microstructure with the fracture toughness and tensile properties.It was found that large numbers of fine αs precipitates and continuous αGB played greater roles than other features,resulting in a high strength and very low ductility(＜2％)of STA process samples.The β grain size had a negative correlation with fracture toughness.In the samples prepared by BASCA(β anneal slow cooling and ageing)process,improved ductility and fracture toughness were ob-tained due to a lower density of αs precipitates,a basket-weave structure and zigzag morphology of αGB.For this heat treatment,an increase in prior β grain size had an observable positive effect on fracture toughness.The contradictory effect of β grain size on fracture toughness found in literature was for the first time explained.It was shown that the microstructure obtained from different processes after β solu-tion has complex effect on mechanical properties.This complexity derived from the competition between microstructure features and the overall sum of their effect on fracture toughness and tensile properties.A novel table was proposed to quasi-quantitatively unravel these competitive effects.
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