查看更多>>摘要：The stray crystal in the platform region is one of the common main defects in single-crystal superal-loy blades.The simple and effective method to eliminate this defect is urgent to be explored.This work found that the Cusp magnetic field can effectively inhibit the stray-crystal formation in the platform.The tendency of stray-crystal formation decreases as the magnetic-field strength increases at a certain with-drawal rate and temperature-gradient.The suppressing effect decreases as the withdrawal rate or the temperature-gradient increases.Finally,the inhibiting mechanism on the stray-crystal formation from the Cusp magnetic field is proposed based on the experiments and the numerical simulation.The magnetic-field application strengthens the flow velocity and changes the flow structure near the liquid-solid in-terface,and further reduces the radial temperature difference.Accordingly,the secondary dendrites in the heat-conduction undercooled zone expands towards the corner in a faster speed,which reduces the stray-crystal formation in the platform corner.This study provides an effective and simple method for decreasing the stray-crystal formation during the preparation of single-crystal with platform region.
查看更多>>摘要：Exfoliated 2D MAX Ti3AlC2 conductive cocatalyst anchored with g-C3N4/TiO2 to construct 2D/0D/2D het-erojunction has been explored for enhanced CO2 photoreduction in a fixed-bed and monolith photoreac-tor.The TiO2 particle sizes(NPs and MPs)were systematically investigated to determine effective metal-support interaction with faster charge carrier separation among the composite materials.When TiO2 NPs were anchored with 2D Ti3AlC2 MAX structure,10.44 folds higher CH4 production was observed com-pared to anchoring TiO2 MPs.Maximum CH4 yield rate of 2103.5 μmol g-1 h-1 achieved at selectivity 96.59％using ternary g-C3N4/TiO2/Ti3AlC2 2D/OD/2D composite which is 2.73 and 7.45 folds higher than using binary g-C3N4/Ti3AlC2 MAX and TiO2 NPs/Ti3AlC2 samples,respectively.A step-scheme(S-scheme)photocatalytic mechanism operates in this composite,suppressed the recombination of useful electron and holes and provides higher reduction potential for efficient CO2 conversion to CO and CH4.More im-portantly,when light intensity was increased by 5 folds,CH4 production rate was increased by 3.59 folds under visible light.The performance of composite catalyst was further investigated in a fixed-bed and monolith photoreactor and found monolithic support increased CO production by 2.64 folds,whereas,53.99 times lower CH4 production was noticed.The lower photocatalytic activity in a monolith photore-actor was due to lower visible light penetration into the microchannels.Thus,2D MAX Ti3AlC2 composite catalyst can be constructed for selective photocatalytic CO2 methanation under visible light in a fixed-bed photoreactor.
查看更多>>摘要：In this study,the effects of annealing and solution aging heat treatment on the microstructure and me-chanical properties of cold spray additive manufactured(CSAMed)AA2024/Al2O3 composite were inves-tigated.The results showed that both annealing and solution aging enhanced the interfacial bonding be-tween the deposited AA2024 particles in the composite.The tensile properties of CSAMed AA2024/Al203 composite were significantly improved by 13.8％for ultimate tensile strength and 47.8％for elongation af-ter solution aging.Microstructural examination and fractographic analysis showed that the fracture mech-anism between the adjacent AA2024 particles changed from brittle to ductile-dominant mode after heat treatment.However,the interfacial bonding between the AA2024 and A1203 particles cannot be improved.For the improvement of mechanical properties,the solution aging was slightly better than annealing.In addition,low-temperature annealing greatly reduced the anisotropy of the mechanical properties of CSAMed AA2024/Al203 composite.
查看更多>>摘要：A β-Ti dendrite reinforced Zr-based bulk metallic glass composite(BMGC)was found to be brittle when cast in a large size.The reasons for the embrittlement and the effectiveness of the cryothermal cycling(CTC)treatment in restoring the mode I fracture toughness are examined.Plasticity in all the CTC treated BMGC is estimated from the distribution and occurrence of pop-ins in nanoindentation tests and by mea-suring the magnitude of enthalpy of relaxation(△Hrel)via differential scanning calorimetry(DSC).This is further validated by examining the strain-to-failure(ef)in compression tests.Mode I fracture behaviour of the as-cast embrittled BMGC and the CTC treated BMGC,which exhibits maximum plasticity,is exam-ined.Results show that both BMGCs are equally brittle and exhibit 5 times lower notch toughness(KQJ)than their tougher counterpart.Post-facto imaging of the side surfaces reveals the absence of notch-tip plasticity in both BMGCs.The lack of notch tip plasticity of CTC treated BMGC,despite exhibiting signa-tures of plasticity in nanoindentation and higher △Hrel is rationalized by reassessing the origin of pop-ins in nanoindentation tests and describing the variations in chemical and topological short range ordering during CTC,respectively.Implications of these results in terms of improving the fracture toughness of structurally relaxed BMGCs via CTC are discussed.
Qingfang HuangQingzheng JiangJifan HuSajjad Ur Rehman...
236-242页
查看更多>>摘要：Post-sinter annealing process plays an important role in the microstructures and magnetic properties of the Nd-Fe-B sintered magnets.In this paper,systematically investigated are the magnetic properties and microstructures of the as-sintered and post-sinter annealed Nd-Fe-B magnets with Pr-Fe-Ga boundary addition.Two choice consecutive annealing methods are adopted at high and low temperatures,namely the 1st annealing at 880℃for 2 h and then the 2nd annealing at 440℃for 3 h.It is exceptional to find out that both the remanence and coercivity are improved after 2nd annealing process for this type of magnet.The coercivity is hugely increased from 10.09 kOe for the as-sintered sample to 17.19 kOe for the 2nd annealed magnet,with a significant increment of 70.37％in coercivity.The extraordinary magnetic properties of Br=14.44 kGs,Hcj=17.19 kOe and(BH)max=51.08 MGOe are obtained for the designated Nd-Fe-B sintered magnets without heavy rare earth(HRE)elements manufactured by dual alloy method.The Curie temperature is monotonically decreased from 634 K to 602 K while the c-axis alignment degree is optimized after annealing.Microstructural observation and analysis indicate that the elemental distribu-tion patterns are altered after the 2nd annealing.The diffusion of the aggregate(Pr,Nd,Cu,Ga)-rich phase from triple junctions into the grain boundary regions is ascribed to the formation of thin and continuous grain boundary layer,which is critical to improve the microstructures and magnetic properties.
查看更多>>摘要：The investigation of two-dimensional(2D)materials has advanced into practical device applications,such as cascaded logic stages.However,incompatible electrical properties and inappropriate logic levels re-main enormous challenges.In this work,a doping-free strategy is investigated by top gated(TG)MoS2 field-effect transistors(FETs)using various metal gates(Au,Cu,Ag,and Al).These metals with different work functions provide a convenient tuning knob for controlling threshold voltage(Vth)for MoS2 FETs.For instance,the Al electrode can create an extra electron doping(n-doping)behavior in the MoS2 TG-FETs due to a dipole effect at the gate-dielectric interface.In this work,by achieving matched electrical properties for the load transistor and the driver transistor in an inverter circuit,we successfully demon-strate wafer-scale MoS2 inverter arrays with an optimized inverter switching threshold voltage(VM)of 1.5 V and a DC voltage gain of 27 at a supply voltage(VDD)of 3 V.This work offers a novel scheme for the fabrication of fully integrated multistage logic circuits based on wafer-scale MoS2 film.
查看更多>>摘要：High lattice thermal conductivity of intrinsic GeTe limits the wide application of GeTe-based thermo-electrics.Recently,the optimization of GeTe-based thermoelectric materials has been focusing on re-ducing lattice thermal conductivity via strengthening phonon scattering.In this study,we systematically studied thermoelectric properties of Se-alloyed Ge0.95Bi0.05Te via theoretical calculations,structural char-acterizations,and performance evaluations.Our results indicate that Se-alloying can induce dense point defects with mass/strain-field fluctuations and correspondingly enhance point defect phonon scattering of the Ge0.95Bi0.05Te matrix.Se-alloying might also change chemical bonding strength to introduce resonant states in the base frequency of Ge0.95Bi0.05Te matrix,which can strengthen Umklapp phonon scattering.Finally,a decreased lattice thermal conductivity from～1.02 W m-1 K-1 to～0.65 W mr1 K-1 at 723 K is obtained in Ge0.95Bi0.05Te1-xSex pellets with increasing the Se content from 0 to 0.3.A peak figure of merit of～1.6 at 723 K is achieved in Ge0.95Bi0.05Te0.7Se0.3 pellet,which is～77％higher than that of pris-tine GeTe.This study extends the understanding on the thermoelectric performance of GeTe.
查看更多>>摘要：A novel Ni30Cr25Al15Co15Mo5Ti5Y5 high-entropy alloy(HEA)coating was irradiated to optimize its inter-nal structure via laser after supersonic particle deposition(SPD).Owing to the high energy density of the laser and large temperature gradient,the crystallization process of the molecules and atoms in the coat-ing was restrained and supercooling occurred.Experimental results showed that a considerable number of nano-crystal grains precipitated and amorphous structures were formed because of the random ori-entation of the crystals.The baseline of differential scanning calorimetry scans obtained for the coating started to shift at the Tg of 939.37℃and a step was observed.Multiple dispersion peaks and lattice fringes indicated that the nucleation of the irradiated laser-induced topology optimized(LTO)coating was incomplete.The laser-induced topology optimizing treatment led to quasi-isotropy in the SPD coat-ing.Furthermore,the LTO coating exhibited a residual stress of 18.4 MPa,stress-strain response,and fatigue limit of 265 MPa.Hence,the LTO coating exhibited higher performance than the unirradiated SPD coating.The Nyquist and Bode electrochemical impedance spectra of the LTO coating,including two re-laxation processes,indicated that the corrosion process steadily recovered to the equilibrium state.This implies that the uniform oxidation passivation layer on the surface of the LTO coating insulated the ma-terial from the corrosive medium,protecting the substrate from further corrosion,thus enhancing the structural security of the material for use in super-intense laser facility applications.
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