查看更多>>摘要：Selective laser melting(SLM)has the advantage in preparing supersaturated solid solutions due to its unique thermal field and high solidification rate.In this study,a face-centered cubic single-phase FeCrNi medium entropy alloy(MEA)with an ultrahigh Cr content(～35 at.％)was additively manufactured by SLM.The as-built MEA shows a hierarchical microstructure of coarse columnar grains and submicron dislocation cell structures,where the cell boundaries are probed segregated with Cr and C and decorated with nano carbides.The appearance of these dislocation barriers results in an excellent combination of strength(σ0.2=745 MPa,σUTS=1007 MPa)and ductility(εf=31％).The current MEA also shows a superb corrosion resistance with a corrosion current density of 0.06 μA cm-2 in 3.5 wt.％NaCl solution,which is far lower than that of 316 L.The high content of solutioned Cr in the MEA ensures sufficient Cr supply to form an integrated Cr2O3 passive film,and the large number of cell boundaries acting as the diffusion channels lead to the fast formation of a stable passive film over the alloy surface.
查看更多>>摘要：The density functional theory(DFT)calculations have been performed to investigate the catalytic prop-erties of monolayer MoSi2N4 for hydrogen evolution reaction(HER).The DFT results show that similar to the majority of other two-dimensional(2D)materials,the pristine MoSi2N4 is inert for HER due to its weak affinity toward hydrogen,while monolayer MoSi2N4-x(x=0-0.25)exhibits the highly desirable HER catalytic activities by introducing surface nitrogen vacancy(NV).The predicted HER overpotential(0-60 mV)of monolayer MoSi2N4-x is lower than that(90 mV)of noble metal Pt,when the concentra-tion of surface NV is lower than 5.6％.Electronic structure calculations show that the spin-polarized states appear around the Fermi level after introducing surface NV,thus making the surface NV on 2D MoSi2N4 a quite suitable site for HER.Moreover,the HER activity of MoSi2N4-x is highly dependent on the surface NV concentration,which can be further related to the center of Si-3p band.Our results demonstrate that the newly discovered 2D MoSi2N4 can be served as a promising electrocatalyst for HER via appropriate defect engineering.
查看更多>>摘要：In this study,surface mechanical attrition treatment was employed to sucessfully produce a gradient nanostructured layer on WE43 magnesium alloy.X-ray diffraction,energy dispersive X-ray spectrometer,and high-resolution transmission electron microscope observations were mainly performed to uncover the microstructure evolution responsible for the refinement mechanisms.It reveals that the grain refine-ment process consists of three transition stages along the depth direction from the core matrix to the topmost surface layer,i.e.,dislocation cells and pile-ups,ultrafine subgrains,and randomly orientated nanograins with the grain size of～40 nm.Noticeably,the original Mg3RE second phase is also expe-rienced refinement and then re-dissolved into the α-Mg matrix phase,forming a supersaturated solid solution nanostructured α-Mg phase in the gradient refined layer.Due to the cooperative effects of grain refinement hardening,dislocation hardening,and supersaturated solid-solution hardening,the gradient nanostructured WE43 alloy contributes to the ultimate tensile strength of～435 MPa and ductility of～11.0％,showing an extraordinary strain hardening and mechanical properties among the reported se-vere plastic deformation-processed Mg alloys.This work provides a new strategy for the optimization of mechanical properties of Mg alloys via combining the gradient structure and supersaturated solid solu-tion.
查看更多>>摘要：Self-lubricating polyphenylene sulfide(PPS)composites were fabricated by constructing a segregated net-work structure using the co-deposition method.Both carboxyl-functionalized multi-walled carbon nan-otubes(CNTs)and silicon carbide(SiC)were successfully coated on the surface of PPS powders with the aid of self-polymerization of dopamine(PDA)and co-polymerization between PDA and polyethyleneimine(PEI),thereby forming PPS@PDA-CNTs-SiC hierarchical reinforcing hybrids.Results showed that the ther-mal conductivity of PPS@PDA-CNTs-SiC(0.97 W/(m K))is about 120％higher than that of PPS/CNTs/SiC.The friction coefficient(0.193)and specific wear rate(2.50×10-5 mm3/(N m))of PPS@PDA-CNTs-SiC are 18.9％and 50％lower than those of PPS/CNTs/SiC,respectively.The enhanced thermal conductivity of PPS@PDA-CNTs-SiC contributes to rapid dissipation of frictional heat at the sliding interface which protects the polymer substrate from being destroyed or peeled,thereby improving the tribological per-formance.This work provides new insights into expanding the application of self-lubricating polymer composites in the fields where efficient heat dissipation is also a primary concern.
查看更多>>摘要：Hall-Petch slope(k),an important parameter in Hall-Petch relation,describes the efficiency of strength-ening effect by grain boundaries.Previously,a highly texture dependent k for Mg alloys is frequently reported,but,in the present study,we report a weak texture dependence of k in a rare-earth containing Mg-2Zn-1Gd plate with two peaks of(0002)poles inclining approximately±30 ° away from the ND to-ward the TD.Although there is a strong mechanical anisotropy between tension along the TD and RD,the k for TD-tension(280 MPa μm1/2)is quite similar to that for RD-tension(276 MPa μm1/2).Here,RD,TD and ND refer to the rolling direction,transverse direction and normal direction of the plate,respectively.The weak texture dependence of k is well predicted by the compound use of the activation stress dif-ference between neighboring grains(△Stress)and the geometric compatibility factor(m').By analyzing how the texture affects the values for △Stress and m',the mechanism for this texture independence of k is ascribed to the activation of a high fraction of additional deformation mode,besides the predominant one for both RD-tension and TD-tension,namely,prismatic slip accompanied by a high fraction of basal slip for RD-tension and basal slip accompanied by a high fraction of prismatic slip for TD-tension.This will lead to multiple deformation transfer modes and,consequently,the effect of texture on the ease of deformation transfer across grain boundaries is weakened.As a result,there is a similar k for TD-tension and RD-tension.
查看更多>>摘要：Durable and cost-effective electrode materials are essential for practical application of supercapacitors.Herein,large area NiCo2O4/reduced graphene oxide(NiCo2O4/rGO)composites with hierarchical structure were fabricated by a facile one-step ultrasonic spray on Ni foam and directly used as the binder-free electrodes for supercapacitors in aqueous KOH electrolyte.Owing to high electrical conductivity of rGO,hierarchical and layered structure of the electrode,as well as tight adhesion of active materials on the current collector,the as-obtained hybrid electrodes show a high specific capacitance of 871 F g-1 at cur-rent density of 1 A g-1,good rate performance and remarkable cycling stability with a capacitance re-tention of 134％after 30000 cycles.Besides,the assembled NiCo2O4/rGO//AC asymmetric supercapacitor(ASC)displays the maximum energy density of 29.3 Wh kg-1 at a power density of 790.8 W kg-1.Signif-icantly,an ultralong cycling life of 102％capacitance retention is achieved for the ASC device after 30,000 charge/discharge cycles at 20 A g-1.The scalable fabrication route and excellent electrochemical perfor-mance of the NiCo2O4/rGO composites open the door for making novel hybrid electrodes of advanced supercapacitors.
查看更多>>摘要：Developing bifunctional electrocatalysts with improved efficiency and stability in overall water splitting is of extreme importance for renewable energy utilization.In this work,an in situ N doping strategy was demonstrate to boost the efficiency and stability of nickel molybdenum sulfide both in electrocatalytic hydrogen evolution reaction and oxygen evolution reaction.Experimental and theoretical results indicate that such modification offers enriched active sites for electrochemical reaction,and further increases the kinetic driven force of water electrolysis.As a result,the N-NiMoS electrode exhibits a remarkably im-proved performance with rather low potential of 1.54 V to offer a current density of 10 mA cmr-2 for overall water splitting,which is 130 mV decrease than that of pristine one.In addition,impressive elec-trochemical stability also reveals a 76.6％preservation of initial current density after 100 h test,which is superior than that of pristine one after 25 h test.Therefore,the potential to enhance the performance of electrocatalysts by as-proposed route promises a valuable way to develop efficient catalysts with en-hanced property for electrochemical applications.
查看更多>>摘要：To investigate the effect of surface-modified nanoparticles(NPs)on the inclusion refinement and mi-crostructure evolution,deoxidized experiment ingots with different amounts of modified NPs were man-ufactured under different cooling conditions.Laser scanning confocal microscope(LSCM)was hereby used for in-situ observation of the phase transition and microstructural evolution during heat cycle process.The results revealed that the inclusion size was always smaller under water quenching than under air cooling,and the number of inclusions was greater under water quenching.After NP addition,the nucle-ant inclusions were identified as MgAl2O4 spinel and irregular TiN inclusion from SEM-EDS measurement and equilibrium calculations using Factsage thermodynamic software.The higher cooling rate under water quenching resulted in less polygonal ferrite decrease and the formation of bainite in the steel.The LSCM experiments showed that ferrite side plates(FSP)always formed on the boundary prior to the formation of acicular ferrite(AF)on the intragranular inclusions,and the start transformation temperatures of FSP and AF phases both lowered after NP addition.The higher cooling rate and NP addition contributed to AF formation and increased the degree of interlocking of the AF phase.Finally,the relationship between the characteristics of inclusions and the kinetics of AF was investigated.
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