查看更多>>摘要：Metamaterials refer to a class of artificial composite structures with supernormal physical properties that natural materials do not have.The emergence of metamaterials has opened up new research directions for classical electromagnetic theory and made it possible to manipulate electromagnetic waves effectively.One of most important applications of metamaterials is metamaterial absorbers(MMAs).The properties of MMAs depend on the material composition,cell size and structure,which could often achieve"perfect"absorption through reasonable design.This review starts with the development of MMAs and describes the status of this absorber,then mainly focuses on bionic design and new artificial design.Specifically,it is to draw inspiration from natural plants and animals,design novel structures to get better absorbing properties.Furthermore,the artificial design can achieve the optimize absorption capacity as well as ab-sorption bandwidth.What's more,this review summarizes the 3D printing technology to prepare MMAs that are different from traditional printed circuit board technology.The MMAs produced by 3D printing technology can prepare more complex shapes,and has light weight and better absorbing properties.
查看更多>>摘要：Due to native character of thermal expansion coefficient(CTE)mismatch between Cf/SiC and GH3536,achieving high strength joint was a huge challenge for Cf/SiC-GH3536 joints.Herein,a composite filler metal of Ag-Cu-Ti+Sc2(WO4)3 was developed to join Cf/SiC and GH3536.This work introduced Sc2(WO4)3 to Ag-Cu-Ti system as a negative thermal expansion(NTE)reinforcing phase to release joint residual stress.Sc2(WO4)3 was evenly distributed in the brazing seam and reacted with Ti to form Ti3O5 reaction layer.The results of finite element analysis showed that the residual stress of the joints was ef-fectively released by introducing Sc2(WO4)3 reinforcing phase,and the mises stress was decreased from 447 to 401 MPa.The maximum shear strength of the Cf/SiC-GH3536 joint brazed with Ag-Cu-Ti+6 vol％Sc2(WO4)3 filler alloys was 64 MPa,which was about 2.6 times higher than that of Ag-Cu-Ti alloys.The results of this study provide a promising strategy for the introduction of new Sc2(WO4)3 reinforcing phase in Ag-Cu-Ti system,and improve the reliability and feasibility of composite brazing alloy in brazing filed.
查看更多>>摘要：Nowadays,SiO2 based material is one of the widest used materials in optical,microelectromechanical system,aerospace and some other industries.In practical application,SiO2 based materials are required to be joined with themselves or other heterogeneous materials to assemble products with various func-tions.And the joining quality directly affects the mechanical performances and functional properties of assembled products.Though many researchers studied different joining technologies,explored the mi-crostructure of joining interface and tested after-joining properties,a review that summarizes the re-cent cutting-edge researches and development tendency of joining technologies for SiO2 based ceramics is still absent.Therefore,according to different applications and requirements,this review summarizes the widely used joining technologies and discusses corresponding joining mechanisms,current research progress and suitable applications.Due to the wide applications in specific industry,laser welding,an-odic bonding and wafer bonding are discussed in detail.Further,brazing,the widest used method in SiO2 joining,has been elaborated deeply in its wetting mechanism,residual stress control,interfacial microstructure and mechanical performance aspects.In the end,this review proposed the future devel-opment trends of SiO2 ceramics joining,aiming at offering a full-view of potential improvements in SiO2 ceramic joining technologies.
查看更多>>摘要：Transformation-induced plasticity(TRIP)endows material with continuous work hardening ability,which is considered as a powerful weapon to break the strength-ductility tradeoff.However,FCC based alloys with TRIP effect can not get rid of the"soft"feature of the structure entirely,resulting in insufficient yield strength.Here,a CoxCr25(AlFeNi)75-x high-entropy alloy is designed.NiAl phase is used as strength-ening component to improve yield strength,while TRIP effect ensures plasticity.Compared with the pre-vious TRIP high-entropy alloy,its yield strength is nearly doubled,and the uniform elongation is more than 55％at room temperature.Furthermore,the corresponding multiphase microstructure evolution and deformation mechanisms are investigated.Significantly,stacking faults and Σ3 twin boundaries are con-firmed to be the nucleation sites of HCP phase by HAADF-STEM.Ingenious composition design and proper heat treatment process make it a perfect combination of precipitation strengthening and transformation-induced plasticity,and thus guide design in the high-performance alloy.
查看更多>>摘要：Flexible aqueous energy storage devices with high security and flexibility are crucial for the progress of wearable energy storage.Particularly,aqueous rechargeable Ni-Fe batteries owning a large theoretical ca-pacity,low cost and outstanding safety characteristics have emerged as a promising candidate for flexible aqueous energy storage devices.Herein,Cu-doped Fe3O4(CFO)with 3D coral structure was prepared by doping Cu2+based on Fe3O4 nanosheets(FO).Furthermore,the Fe-based anode material(CFPO)grown on carbon fibers was obtained by reconstructing the surface of CFO to form a low-crystallization shell which can enhance the ion transport.Excitingly,the newly developed CFPO electrode as an innovative anode material further exhibited a high capacity of 117.5 mAh g-1(or 423 F g-1)at 1 A g-1.Then,the assem-bled aqueous Ni-Fe batteries with a high cell-voltage output of 1.6 V deliver a high capacity of 49.02 mAh g-1 at 1 A g-1 and retention ratio of 96.8％for capacitance after 10 000 continuous cycles.What's more,the aqueous quasi-solid-state batteries present a remarkable maximal energy density of 45.6 Wh kg-1 and a power density of 12 kW kg1.This work provides an innovative and feasible way and optimization idea for the design of high-performance Fe-based anodes,and may promote the development of a new generation of flexible aqueous Ni-Fe batteries.
查看更多>>摘要：Advanced bainitic steels with the multiphase structure of bainitic ferrite,retained austenite and marten-site exhibit distinctive fatigue crack initiation behavior during high cycle fatigue/very high cycle fatigue(HCF/VHCF)regimes.The subsurface microstructural fatigue crack initiation,referred to as"non-inclusion induced crack initiation,NIICI",is a leading mode of failure of bainitic steels within the HCF/VHCF regimes.In this regard,there is currently a missing gap in the knowledge with respect to the cyclic response of multiphase structure during VHCF failure and the underlying mechanisms of fatigue crack initiation during VHCF.To address this aspect,we have developed a novel approach that explicitly identi-fies the knowledge gap through an examination of subsurface crack initiation and interaction with the lo-cal microstructure.This was accomplished by uniquely combining electron microscopy,three-dimensional confocal microscopy,focused ion beam,and transmission Kikuchi diffraction.Interestingly,the study indi-cated that there are multiple micro-mechanisms responsible for the NIICI failure of bainitic steels,includ-ing two scenarios of transgranular-crack-assisted NIICI and two scenarios of intergranular-crack-assisted NIICI,which resulted in the different distribution of fine grains in the crack initiation area.The fine grains were formed through fragmentation of bainitic ferrite lath caused by localized plastic deformation or via local continuous dynamic recrystallization because of repeated interaction between slip bands and prior austenite grain boundaries.The formation of fine grains assisted the advancement of small cracks.An-other important aspect discussed is the role of retained austenite(RA)during cyclic loading,on crack ini-tiation and propagation in terms of the morphology,distribution and stability of RA,which determined the development of localized cyclic plastic deformation in multiphase structure.
查看更多>>摘要：The 5.0 vol.％GNP/2024AI composites were prepared by accumulated shear deformation combined with heat treatment,i.e.the thermomechanical treatment(TMT).The results showed that homogeneous dis-tributed GNPs that aligned along the plastic deformation direction were obtained by six-pass drawing in the solution heat treatment state.The introducing of high-density dislocations in Al matrix by multiple drawing resulted in enhanced nucleation of precipitates and subsequent uniform growth during ageing.Consequently,ultra-strength GNP/2024A1 composites,with yield and ultimate tensile strength 482 and 571 MPa,respectively,were achieved.The high strength was attributed to homogeneous dispersion of undamaged GNPs,fine and dispersed precipitations and work-hardening effect.This work demonstrated that TMT could act as a feasible strategy for preparing high-performance GNP/Al composites.
查看更多>>摘要：The new near-α TNW700 titanium alloy is a potential candidate material for high performance ultra-sonic/hypersonic aircrafts,which is designed for short-term service at 700℃.This study systematically investigated the superplastic deformation microstructure evolution and mechanism of TNW700 alloy at different strain rates and true strains at 925℃.Results show that TNW700 alloy exhibits excellent super-plastic behavior in a constant strain rate range of 0.0005-0.005 s-1 with elongation above 400％.The peak stress decreases with decreasing strain rate,which is related to the increase ofβ-phase volume fraction caused by the increase of thermal exposure time.In addition,significant strain hardening is observed in early-middle stage of superplastic deformation,and flow softening is followed in middle-late stage.To ra-tionalize these complex flow behaviors,electron backscatter diffraction(EBSD)and high resolution trans-mission electron microscopy(HRTEM)were used to characterize the microstructure.Strain hardening is correlated to the synergistic effect ofβ grain growth,dislocation accumulation,silicide precipitate,and solid solution strengthening of α phase.Continuous dynamic recrystallization(CDRX)induced the frag-mentation of primary α grains in middle-late stage of superplastic deformation,and the refinement of αgrains,the increase of β phase volume fraction and dynamic dislocation recovery are main causes of high strain softening.In addition,EBSD and TEM observations confirmed texture randomization,fine equiaxed primary α grains and intragranular dislocation movement,indicating that grain boundary sliding(GBS)accommodated by dislocation sliding/climb is the dominant superplastic deformation mechanism of TNW700 alloy.
查看更多>>摘要：Structure,magnetic properties and ductile of melt-spun Fe83-xSi4B13-yCyCux(x=0-1.7;y=0-8)alloys were investigated.The addition of 1.7 at.％Cu in a Fe83Si4B13 amorphous alloy generates abundant α-Fe crystals by providing nucleation sites,and further C doping promotes the growth of the crystals by suitable turning amorphous-forming ability,hence they increase saturation magnetic flux density(Bs)and slightly worse magnetic softness of the as-spun alloys.The as-spun Fe81.3Si4B7C6Cu1.7 alloy possesses a combined structure of a fully amorphous layer in wheel side surface and predominating nanocrystalline structure with gradually enlarged α-Fe crystal,whose average size and volume fraction are determined as about 12 nm and 32％,respectively,therefore superior soft magnetic properties and ductile with a high Bs of 1.74 T,coercivity(Hc)of 32.7 A/m,effective permeability(μe,at 1 kHz)of 3200 and high relatively strain at fracture(εf)of 3.61％can be achieved directly in this alloy by only using melt-spinning.The annealing at 578 K releases internal stress,promotes the growth of the α-Fe crystals and remains the amorphous layer of the Fe81.3Si4B7C6Cu1.7 alloy,then improves the soft magnetic properties and maintains the superior ductile with increasing the Bs and μe to 1.80 T and 14,100,respectively,lowering the Hc to 9.4 A/m and slightly reducing the εf to 2.39％.The combination of superior soft magnetic properties and ductile and simplified synthesis process entitles the Fe-Si-B-C-Cu nanocrystalline alloys great potentials in high performance electromagnetic applications.
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