查看更多>>摘要：Ti-6.5Al-2.5Sn-9Zr-0.5Mo-0.25Si-1Nb-1W-0.1Er-xB(x=0,0.1,0.2,0.4,0.6 and 0.8 wt％)with different boron contents are fabricated for investigation.Influences of boron element and its amounts on phase constitutions,microstructures,textures and compression mechanical properties are carefully studied.With the increasing boron additions,contents of TiB phase increase,and the maximum intensities of tex-tures decrease.Microstructures are significantly and continuously refined after adding boron element and with the increasing boron additions,and turning point of refinement rates for different microstruc-tural parameters is found at 0.2 wt％boron content.Strengths increase monotonously,while elongations increase firstly and decrease afterwards.The maximum value of elongation is acquired at boron con-tent of 0.2 wt％.On the premise of ensuring plasticity,0.2 wt％boron content is the most appropriate amount for microstructural refinement and mechanical properties enhancement for current near α tita-nium alloys.Meanwhile,aspect ratios of TiB whiskers increase with the increasing boron contents.Lots of near equiaxed α grains or α grains with irregular morphologies are discovered around TiB phase.Dis-torted and twisted α grain boundaries are also obviously detected in boron containing alloys.Moreover,premature fracture of alloys containing TiB whiskers is largely influenced by the fracture of these brittle reinforcements.
查看更多>>摘要：A novel three-dimension separable and recyclable rGH-PANI/BiOI photocatalyst with the synergism of adsorption-enrichment and photocatalytic-degradation was successfully prepared via a facile three-step hydrothermal method.The three-dimension reduced graphene oxide hydrogel(rGH)in with flower-like BiOI photocatalyst uniformly distributed not only possesses excellent adsorption and electron transport properties,but also is easy to be separated from water for recycling.In addition,polyphenylamine(PANI)provides superior hole transport ability due to its delocalized π-π conjugate structure.The cooperation of rGH and PANI greatly enhances the separation efficiency of photogenerated carriers,and finally improves the photocatalytic degradation behaviors.The removal rates of Rhodamine B(RhB)by rGH-PANI/BiOI-70％composite under visible light respectively reach 100％and 50.13％in static and dynamic systems,which are 12.85 and 3.58 times of BiOI,respectively.The removal rate does not show decrease after 5 recycles indicating the excellent separable and recyclable property of rGH-PANI/BiOI photocatalyst.The work provides an essential reference for designing and constructing hydrogel-based ternary composite photocatalysts with excellent synergism of adsorption and photocatalysis,which shows great potential in the treatment of water pollution.
查看更多>>摘要：Liquid dynamics plays an essential role in glass formation.Here we observed a distinct change of liquid dynamics in Gd55Co20Al25 metallic glass induced by microalloying Si element.In the equilibrium melt,minor Si(0.5 at.％)addition leads to a more fragile liquid behavior and a smaller strength of liquid-liquid transition with the transition strength(ΔF)decreasing from 0.76 to 0.35.However,in the supercooled liquid,Si-doped liquid exhibits a remarkable enhanced fragile-to-strong transition(FST),and the value of FST factor f increases sharply from 1.63 to 3.84,resulting in a stronger liquid behavior and more sluggish crystallization kinetics for Gd55Co20Al24.5Si0.5 metallic glass.Moreover,minor Si addition promotes the formation of a crystal-like structure with a size of 1-2 nm.The interactions between the crystal-like structures and other local favored clusters frustrate the further growth of crystal-like phases,thus sta-bilizes the amorphous structure.As a result,the glass-forming ability(GFA)was largely improved.The critical diameter of Gd55Co20Al25 metallic glass increased from 2 to 7 mm with 0.5 at.％Si addition with-out deterioration of the magnetocaloric effect.This study provides valuable insight for understanding the distinct effect of microalloying on GFA of metallic glasses from the aspect of the evolution of the liquid.
查看更多>>摘要：Laser aided additive manufacturing(LAAM)was used to fabricate bulk Fe49.5Mn30Co10Cr10C0.5 interstitial multicomponent alloy using pre-alloyed powder.The room temperature yield strength(σy),ultimate tensile strength(σUTS)and elongation(εUST)were 645 MPa,917 MPa and 27.0％respectively.The as-built sample consisted of equiaxed and dendritic cellular structures formed by elemental segregation.These cellular structures together with oxide particle inclusions were deemed to strengthen the material.The other contributing components include dislocation strengthening,friction stress and grain bound-ary strengthening.The high εUTS was attributed to dislocation motion and activation of both twinning and transformation-induced plasticity(TWIP and TRIP).Tensile tests performed at-40℃and-130℃demonstrated superior tensile strength of 1041 MPa and 1267 MPa respectively.However,almost no twinning was observed in the fractured sample tested at-40℃and-130℃.Instead,higher fraction of strain-induced hexagonal close-packed(HCP)ε phase transformation of 21.2％were observed for fractured sample tested at-40℃,compared with 6.3％in fractured room temperature sample.
查看更多>>摘要：The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated.The two-stage heat treatment experiments include an aging annealing treatment(AT)and a subsequent recrystallization annealing treatment(RT).The object of AT is to precipitate some δ phases and consume part of storage energy to inhibit the grain growth during RT,while the RT is to refine mixed and coarse grains by recrystallization.It can be found that the recrystallization grains will quickly grow up to a large size when the AT time is too low or the RT temperature is too high,while the deformed coarse grains cannot be eliminated when the AT time is too long or the RT temperature is too low.In addition,the mixed microstructure composed of some abnormal coarse recrystallization grains(ACRGs)and a large number of fine grains can be observed in the annealed specimen when the AT time is 3 h and RT tem-perature is 980℃.The phenomenon attributes to the uneven distribution of δ phase resulted from the heterogeneous deformation energy when the AT time is too short.In the regions with a large number of δ phases,the recrystallization nucleation rate is promoted and the growth of grains is limited,which results in fine grains.However,in the regions with few δ phases,the recrystallization grains around grain boundaries can easily grow up,and the new recrystallization nucleus is difficult to form inside grain,which leads to ACRGs.Thus,in order to obtain uniform and fine annealed microstructure,it is a prereq-uisite to precipitate even-distributed δ phase by choosing a suitable AT time,such as 12 h.Moreover,a relative high RT temperature is also needed to promote the recrystallization nucleation around δ phase.The optimal annealing parameters range for uniformly refining mixed crystal can be summarized as:900℃×12 h+990℃×(40-60 min)and 900℃×12 h+1000℃×(10-15 min).
查看更多>>摘要：A novel equimolar high-entropy(HE)transition metal monoboride,(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B,was designed and prepared in powder and bulk form by high temperature elemental reac-tion method and spark plasma sintering(SPS)method,respectively.XRD analysis shows that HE(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B possesses orthorhombic structure with Pnma space group.Through Rietveld refinement,the lattice parameters of HE(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B are a=5.6675,b=2.9714,c=4.2209 and the theoretical density is 6.95 g/cm3.The Vickers hardness and electrical conductivity of HE(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B bulk with relative density of 90％is 12.3±0.5 GPa and 0.49±0.04×106 S/m,respectively.Due to high electrical conductivity,HE(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B bulk with 3.0 mm thickness displays superior EMI shielding performance in 18.0-26.5 GHz(K-band),and the average values of SET,SER,and SEA are 23.3 dB,13.9 dB,and 9.4 dB,respectively.The EMI shielding mechanism of HE(Cr0.2Mn0.2Fe0.2Co0.2Mo0.2)B mainly results from reflection.
查看更多>>摘要：The effects of strain rate on the microstructural evolution and deformation mechanism of a Ni-Co based superalloy were investigated by isothermal compression tests performed at γ'sub-solvus(1090℃)andγ'super-solvus temperatures(1150℃)with a wide strain rate range from 0.001 to 10 s-1 under a true strain of 0.693.Electron backscatter diffraction(EBSD),electron channeling contrast imaging(ECCI)and transmission electron microscope(TEM)techniques were used to characterize the microstructures.The results revealed that the dynamic recrystallization(DRX)volume fraction increased and stored energy of the γ matrix grains decreased with increasing the strain rate during γ'sub-solvus temperature defor-mation,while the opposite phenomena were observed during γ'super-solvus temperature deformation.The comprehensive effect of initial grain size,primary y'phase,twins and adiabatic temperature rise led to these results.The primary γ'particles undergone the deformation behavior within itself and obviously accelerated the DRX of the matrix.The microstructural evolution proved that discontinuous dynamic recrystallization(DDRX)was the dominant mechanism during the hot deformation carried out at both γ'sub-solvus and γ'super-solvus temperatures.Primary γ'particles obviously accelerated the nucleation step and retarded the growth step of DDRX during γ'sub-solvus temperature deformation.Besides,the acceleration effect of primary γ'particles on DDRX increased with the increase of strain rate.Continuous dynamic recrystallization(CDRX)was confirmed to be an assistant mechanism during γ'super-solvus temperature deformation and was promoted with the increase of strain rate.
查看更多>>摘要：The undercooling dependence of the solidification mechanism was systematically explored by the elec-trostatic levitation(ESL)facility.During the experiments,the maximum undercooling reached up to 406 K(0.26 TL)and the growth velocity of the primary TiNi phase was in-situ determined at various undercool-ings.At the initial increase of alloy undercooling,the value of growth velocity sluggishly rose followed by a power function.In this case,the primary TiNi phase preferentially developed as the equiaxed dendrite,then the remnant liquid participated as Ti2Ni and α-Ti phases on the grain boundary.Once the under-cooling exceeded the critical value of 350 K,the growth velocity of the primary phase displayed a sharply increase tendency.Meanwhile,the TEM results demonstrated that the precipitation of the intermetallic Ti2Ni compound was gradually restrained during the rapid solidification and the R-phase existing in the TiNi matrix at large undercooling implied that the martensitic transformation was incomplete.
查看更多>>摘要：This study focused on the effect of grain size(GS)on dynamic damage performance of nano-crystalline nickel titanium(NC NiTi)alloy.Molecular dynamics simulations were conducted to triaxially expand it at a high strain rate(4×109 s-1),while the temperature and initial pressure remained 300 K and 0 bar,respectively.It was discovered that the superelastic NiTi alloy exhibited the similar damage response as ductile metallic materials,which was vividly characterized by void nucleation,growth,and coalescence.The stress-strain curves demonstrated that the void nucleations always occurred near the start of the strain softening region at various grain sizes.Interestingly,it was discovered that the void evolution was characteristic of an almost double-linear behavior,and the piecewise linearity became more prominent for the void volume fraction increase at larger grain size.More importantly,the fracture behavior was found to be strongly dependent upon the grain size in the NC NiTi alloy.For small grain size,the existing voids propagated along the grain boundaries and in the grains,leading to intergranular and transgranular fracture.Contrarily,the intergranular-dominated fracture was responsible for the void propagation in the large grain.In addition,the starting time,ending time,and threshold of void nucleation were found to be weak sensitivity to GS,and a reverse effect was appropriate to the void growth.The results highlighted that as the GS increased,more complete stress relaxation and shorter duration time were produced,leading to larger void volume fraction and faster growth rate.
查看更多>>摘要：We report for the first time a Na-ion battery anode material composed of P-doped CoSe2 nanoparticles(P-CoSe2)with the size of 5-20 nm that are uniformly embed in a 3D porous honeycomb-like carbon network.High rate capability and cycling stability are achieved simultaneously.The honeycomb-like carbon network is rationally designed to support high electrical conductivity,rapid Na-ion diffusion as well as the accommodation of the volume expansion from the active P-CoSe2 nanoparticles.In particular,heteroatom P-doping within CoSe2 introduces stronger P-Co bonds and additional P-Se bonds that signif-icantly improve the structure stability of P-CoSe2 for highly stable sodiation/desodiation over long-term cycling.P-doping also improves the electrical conductivity of the CoSe2 nanoparticles,leading to highly elevated electrochemical kinetics to deliver high specific capacities at high current densities.Benefiting from the unique nanostructure and atomic-level P-doping,the P-CoSe2(2∶1)/C anode delivers an excel-lent cycle stability with a specific capacity of 206.9 mA h g-1 achieved at 2000 mA g-1 after 1000 cycles.In addition,this material can be synthesized using a facile pyrolysis and selenization/phosphorization approach.This study provides new opportunities of heteroatom doping as an effective method to improve the cycling stability of Na-ion anode materials.
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