查看更多>>摘要：Porosity is a major issue in solidification processing of metallic materials.In this work,wedge die casting experiments were designed to investigate the effect of cooling rate on microporosity in an aluminum alloy A356.Microstructure information including dendrites and porosity were measured and observed by optical microscopy and X-ray micro-computed tomography (XMCT).The effects of cooling rate on secondary dendrite arm spacing (SDAS) and porosity were discussed.The relationship between SDAS and cooling rate was established and validated using a mathematical model.Three-dimensional (3-D) porosity information,including porosity percentage,pore volume,and pore number,was determined by XMCT.With the cooling rate decreasing from a lower to a higher position of the wedge die,the observed pore number decreases,the porosity percentage increases,and the equivalent pore radius increases.Sphericity of the pores was discussed as an empirical criterion to distinguish the types of porosity.For different cooling rates,the larger the equivalent pore radius is,the lower the sphericity of the pores.This research suggests that XMCT is a useful tool to provide critical 3-D porosity information for integrated computational materials engineering (ICME) design and process optimization of solidification products.
Mohammad Sharear KabirZhifeng ZhouZonghan XiePaul Munroe...
108-117页
查看更多>>摘要：New multilayer coatings were produced by incorporating alternating soft and hard DLC layers enabled by varying the bias voltage during deposition process while maintaining a constant hard-to-soft layer thickness ratio.These coatings were deposited onto a Cr/CrCx graded layer by closed field unbalanced magnetron sputtering (CFUBMS).The cross-sectional analysis of the coatings showed that the multilayer coatings possess sharp interfaces between the soft and hard layers with the hard to soft layer thickness ratio (1:1.33) constant in all the coatings.Raman analysis uncovered the increasing sp3 character of the DLC coatings as a result of decreasing ID/IG ratio and increasing full width at half maximum (FWHM) values of the G band peak induced supposedly by an increase in bias voltage during hard layer deposition.Nanoindentation tests showed an increase in hardness of the DLC coatings which can be correlated with the increase in the sp3 content of the coatings as well as decreasing sp2-C cluster size,as calculated from the ID/IG ratio.Furthermore,the coatings exhibited excellent plastic deformation resistance and adhesion strength upon microindentation and scratch testing,respectively.Although further investigations are required to assess coating durability,the multilayer design could offer the DLC coatings with a rare opportunity to combine the high hardness with damage resistance with a constant bilayer thickness and without the need to introduce complex multilayer system.
查看更多>>摘要：Designing efficient and stable non-precious metal HER (hydrogen evolution reaction) electrocatalysts with high large current density adaptability is significant for industrial application of hydrogen production by water electrolysis.Herein,a facile strategy was developed to construct a multi-phase Ni3P-Co2 P-(Ni-Co) film with self-supporting hierarchically micro/nano-porous structure by using bubble template method electrodeposition of self-supporting micro-porous NiCoP film,oxygen-free annealing for phase separation producing Ni3P-Ni-Co2P-Co structure,and acid etching for constructing surface nano-porous structure.The effective active sites for HER was significantly increased due to the hierarchically micro/nano-porous structure,which not only enlarged the surface roughness,but enhanced the bubble detachment by improving the hydrophilicity.Meanwhile,the HER electrolysis durability was improved benefiting from the Ni3P-Co2P phases with high corrosion resistance (especially in acid solution) and the self-supporting film structure without binder.Consequently,the NiCoP-OA-AE film exhibited high HER catalytic performance,which delivered a current density of 10 mA cm 2 at a low overpotential of 42.9 and 39.7 mV in 1 M KOH and 0.5 M H2SO4,respectively.It also possessed high long-term electrolysis durability,and the cell voltage of water electrolysis using self-supporting porous NiCoP-OA-AE‖IrO2-Ta2O5 electrolyzer at 500 mA cm 2 for 250 h in 0.5 M H2SO4 is only 2.9 V.
查看更多>>摘要：Hot-dip galvanizing provides excellent corrosion and wear resistance for steels.However,the equipment itself,such as the steel roller,immerged in corrosive molten zinc suffers serious material loss during steel's production.Its protection has become the main technique problem in modern galvanizing line.In this study,an enamel coating was designed and prepared.Its tribo-corrosion in molten zinc alloy (Zn-0.2 wt％ Al) at 460 C was investigated in comparison with the traditional WC-12Co composite coating and the 316 stainless steel.Results indicate that the steel suffers serious material damage.Various corrosion products of Fe2Al5Znx form at the worn surface and the wear scar has reached 200 μm deep after merely 5 h tribo-corrosion.Though the two coatings provide an improved tribo-corrosion resistance,for the WC-12Co coating,its chemical reaction with the molten zinc increases brittleness and promotes cracking.The synergistic wear and corrosion cause its degradation.The enamel coating performs better during tribo-corrosion.It is chemically stable in molten zinc thus able to provide high corrosion resistance.In addition,the amorphous[SiO4]network and the self-lubricating CaF2 crystallite help it to build up an intact amorphous glaze layer readily at surface on sliding,leading to a reduced wear loss.During the whole tribo-corrosion process,the enamel coating is completely free of cracking,and the Zn penetration is inhibited.
查看更多>>摘要：The protection of rusted carbon steel in acid corrosion environments is of great significance for equipment to keep safe operation.In this work,we presented a method to protect the rusted steel by rust conversion treatment and epoxy coating.Tannic acid was selected as rust conversion agent.Tannic acid,D-limonene and nano-ZrO2 were used to improve the corrosion resistance of epoxy coatings.The Raman spectra,X-ray diffraction and 3D confocal images were used to characterize the rust conversion reaction.Adhesion test showed that the loss of wet adhesion of the optimal coating was relatively low due to the addition of tannic acid,limonene and nano-ZrO2.The corrosion resistance of five different coatings was investigated by scanning electron microscopy (SEM) and electrochemical analysis.Results show that after 264 h acid immersion,the low frequency resistance of the optimal coating consisting of rust conversion treatment and additives is 107 Ω cm2,three orders magnitude higher than that of the pristine coating.Moreover,SEM indicates that the optimal coating possesses a smooth surface and an unbroken interface between substrate and coating.Accordingly,the corrosion-resistant mechanism of the hybrid coating is proposed.
查看更多>>摘要：With this contribution,as a comment to the publication in Journal of Materials Science & Technology 44 (2020) 54,reporting giant dielectric response,structural characterization and numerical simulations in Sr1-1.5xBixTiO3 ceramics,we show that the reported results are rather contradicting and not well analysed,while the suggested mechanism for the giant permittivity response is not valid or doubtful and has to be reconsidered.Moreover,many details and data are missing making impossible not only to call the obtained results very suitable for practical application but even to reproduce them.
查看更多>>摘要：Air plasma sprayed thermal barrier coatings (APS-TBCs) saw their wide application in high-temperature-related cutting-edge fields.The lamellar structure of APS-TBCs provides a significant advantage on thermal insulation.However,short life span is a major headache for APS-TBCs.This is highly related to the property changes and passive behaviors of the coatings during thermal service.Herein,a finite element model was developed to investigate the dynamic stiffening and substrate constraint on total spallation process.Results show that the stiffening accelerates the crack propagation of APS-TBCs.The driving force for crack propagation,which is characterized by strain energy release rate (SERR),is significantly enlarged.Consequently,the crack starts to propagate when the SERR exceeds the fracture toughness.In addition,the changing trends of SERR and crack propagation features are highly associated with temperatures.A higher temperature corresponds to more significant effect of stiffening on substrate constraint.In brief,temperature-dependent stiffening significantly aggravates the substrate constraint effect on APS-TBCs,which is one of the major causes for the spallation.Given that,lowering stiffening degree is essential to maintain high strain tolerance,and to further extend the life span of APS-TBCs.This understanding contributes to the development of advanced TBCs in future applications.
查看更多>>摘要：Increasing the availability of π-electron in graphitic carbon nitride (g-C3N4) can reduce the band gap and thus enhance the photocatalytic hydrogen (H2) generation activity upon exposure to visible light.However,such strategy has not yet been largely applied to increase the H2 generation of g-C3N4.Herein,we successfully increased the amount of π-electron in g-C3N4 by incorporating π-electron-rich benzene rings through copolymerization of melamine and trimesic acid in air.The incorporation of benzene rings not only extends the light absorption of g-C3N4 to 650 nm,but also improves the electrical conductivity due to delocalization of π electrons in benzene rings.As a result,a 3.4 times enhancement of photocatalytic H2 generation was achieved from the g-C3N4 with benzene ring incorporation in comparing with that of pristine g-C3N4.More interestingly,H2 generation still occurs under irradiation of the light of λ ≥ 490 nm,above the absorption edge of pristine g-C3N4 (～ 460 nm),illustrating the positive effectiveness of incorporated benzene rings on enhancing the H2 generation capacity of g-C3N4.The present work manifests the advantages of increasing T-conjugated electrons on designing highly active g-C3N4 photocatalysts.
查看更多>>摘要：Structure,crystallization behavior,and magnetic properties of as-quenched and annealed Fe81.3Si4B13Cu1.7 (Cu1.7) alloy ribbons and effects of Nb alloying have been studied.Three-dimensional atom probe and transmission electron microscopy analyses reveal that high-number-density Cu-clusters and Pre-existing Nano-sized α-Fe Particles (PN-α-Fe) are coexistence in the melt-spun Cu1.7 amorphous matrix,and the PN-α-Fe form by manners of one-direction adjoining and enveloping the Cu-clusters.Two-step crystallization behavior associated with growth of the PN-α-Fe and subsequent nucleation and growth of newly-formed α-Fe is found in the primary crystallization stage of the Cu1.7 alloy.The number densities of the Cu-clusters and PN-α-Fe in melt-spun Fe81.3-xSi4B13Cu1.7Nbx alloys are gradually reduced with enriching of Nb,and a fully amorphous structure forms at 4 at.％ Nb,although smaller Cu-clusters still exist.After annealing,2 at.％ Nb coarsens the average size (Dα-Fe) of the α-Fe grains from 14.0 nm of the Nb-free alloy to 21.6 nm,and 4 at.％ Nb refines the Dα-Fe to 8.9 nm.The mechanisms of the α-Fe nucleation and growth during quenching and annealing for the alloys with large quantities of PN-α-Fe as well as after Nb alloying have been discussed,and an annealing-induced α-Fe growth mechanism in term of the barrier co-contributed by competitive growth among the PN-α-Fe and diffusion-suppression effect of Nb atoms has been proposed.A coercivity (Hc) ∝ Dα-Fe3 correlation has been found for the nanocrystalline alloys,and the permeability is inverse with the Hc.
查看更多>>摘要：Cu@MOF core-shell nanowires are synthesized by introducing oxidizable and CTAB-modified metal nanowires as self-engaged templates and supporting MOFs for a one-dimension nanostructure.The following thermal process is controlled to obtain several one-dimension structures of CuCo-mixed materials,such as nanorods,single-shell and double-shell nanowires.The hollow structure for electrode materials enlarges the surface area,provides buffer space for electrolyte to accelerate the ion/charge transfers and for the structure to reduce injuries of volume expansion during cycling.Together with some other merits,such as adequate oxidation of the MOFs,small crystal grains of the material,and well-mixed Cu/Co oxides,the double-shell Cu@MOF nanowires (CuCo-DSS) applied for pseudocapacitors deliver advanced electrochemical performance with a specificcapacitanceof563.8 Fg-1 at1Ag-1 as well as an outstanding cycling stability with a 92 ％ retention after 3000 cycles at 5 A g-1.Meanwhile,an asymmetric pseudocapacitor constructed with the CuCo-DS5 and active carbon (AC) shows a high specific capacitance and energy density.
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