查看更多>>摘要：High-temperature titanium alloys'thermal stability and creep resistance are significant during service in high temperatures.This study systematically investigated the thermal stability and mechanical properties of Ti-6.5Al-2.5Sn-9Zr-0.5Mo-1Nb-1W-0.3Si-xSc(x,0-0.5 wt.％)at 650 ℃.The lamellar secondary α phase is refined and the formation of Sc2O3 is increased with the increasing scandium(Sc)additions,which im-proves the strength of the alloy,while excessive Sc2O3 becomes the crack source and deteriorates the plasticity.The oxygen content in the matrix is reduced by the interaction between Sc and oxygen,in-hibiting the growth of the Ti3Al phase and improving the thermal stability of the alloy.Meanwhile,Sc accelerates the dissolution of the residual β phase and precipitation of fine,diffusely distributed ellip-soidal silicides,which strongly prevents dislocation movement.The enhancement of creep resistance for the Sc-containing alloy is attributed to the refined lamellar secondary α phases,Sc2O3 particles,Ti3Al phase,and silicides,especially the precipitated silicides.Eventually,the 0.3Sc alloy shows optimal ther-mal stability(the plasticity loss rate 17.3％)and creep resistance(steady-state creep rate 4.4 x 10-7 s-1).The investigation results provide new insights into the mechanism and thermal stability improvement in high-temperature titanium alloys modified by rare earth(RE).
查看更多>>摘要：The introduction of highly polarized flexible segments into polymer molecular chains is an effective means to improve the dielectric constant and mechanical flexibility of polymers,which is important for improving the energy storage characteristics and applicability for the roll-to-roll process of metallic film capacitors.However,the introduction of flexible segments may adversely affect the heat resistance of polymer materials,which limits their application at high working temperatures.In this work,we have prepared a novel epoxy film with excellent comprehensive properties by introducing rigid phenyl and flexible etherified methylene side chains.For instance,the optimal epoxy film showed an energy storage density of 7.06 J cm-3 and 85％charge-discharge efficiency at room temperature and 420 kV mm-1.At 200 kV mm-1 and 110 ℃,a working condition for the application of the electric vehicle,the prepared film still showed an energy storage density of 1.5 J cm-3 and charge-discharge efficiency of 86％,which is 3 times that of BOPP film.This work provides an idea for material designs of high-performance polymer film capacitors.
查看更多>>摘要：The self-assembly of two-dimensional(2D)semiconductor nanosheets into three-dimensional(3D)or-dered superstructures represents an ingenious way to avoid aggregation,expose massive available active sites and benefit the mass transfer,which maximizes the advantages of the 2D nanostructures in photo-catalysis.Herein,a flower-like superstructure of ternary semiconducting boron carbon nitride nanosheets(FS-BCNNSs)was synthesized through the morphology-preserved thermal transformation of a flower-like superstructure of boron-containing metal-organic framework nanosheets(FS-MOFNSs).Taking advantage of this functional superstructure,FS-BCNNSs was employed for the pioneering application in the field of photocatalytic hydrogen peroxide(H202)production and exhibited excellent photocatalytic performance,yielding an impressive rate of 1415.9 μmol g-1 h-1 for the production of H202.The results of this work offer not just a promising catalyst for photocatalytic H202 production but also a facile strategy to fabri-cate unique superstructures constructed from 2D nanosheets for catalysis,energy conversion,and other related fields.
查看更多>>摘要：Ti and its alloys have been broadly adopted across various industries owing to their outstanding proper-ties,such as high strength-to-weight ratio,excellent fatigue performance,exceptional corrosion resistance and so on.Additive manufacturing(AM)is a complement to,rather than a replacement for,traditional manufacturing processes.It enhances flexibility in fabricating complex components and resolves machin-ing challenges,resulting in reduced lead times for custom designs.However,owing to distinctions among various AM technologies,Ti alloys fabricated by different AM methods usually present differences in mi-crostructure and defects,which can significantly influence the mechanical performance of built parts.Therefore,having an in-depth knowledge of the scientific aspects of fabrication and material properties is crucial to achieving high-performance Ti alloys through different AM methods.This article reviews the mechanical properties of Ti alloys fabricated by two mainstream powder-type AM techniques:powder bed fusion(PBF)and directed energy deposition(DED).The review examines several key aspects,en-compassing phase formation,grain size and morphology,and defects,and provides an in-depth analysis of their influence on the mechanical behaviors of Ti alloys.This review can aid researchers and engi-neers in selecting appropriate PBF or DED methods and optimizing their process parameters to fabricate high-performance Ti alloys for a wide range of industrial applications.
查看更多>>摘要：Single-phase face-centered cubic(fcc)high/medium-entropy alloys(H/MEAs)exhibit a much higher ten-dency to form nanoscale deformation twins than conventional fcc metals with similar low stacking fault energies(SFEs).This extraordinary propensity for nanotwin formation in H/MEAs cannot therefore be ex-plained by their low SFEs alone.Here,using in situ compression tests of CrCoNi in comparison with Ag nanopillars inside a transmission electron microscope,we found that in the CrCoNi MEA,a high density of nanoscale twins continuously formed with an average thickness of 4.6 nm.In contrast,for similar ex-periments on Ag with almost identical SFE,following the nucleation of a few twins,they could further thicken to above one hundred nanometers by twin boundary migration.Molecular dynamics calculations indicated that in the highly-concentrated CrCoNi solid solution,the magnitude of the energy barriers for nucleating a stacking fault as a twin precursor in the pristine lattice and for the thickening of an existing twin both span a wide range and largely overlap with each other.Therefore,twin thickening through suc-cessive addition of atomic layers is prone to discontinuation,giving way to the nucleation of new twins at other sites where a lower energy barrier is encountered for partial-dislocation mediated fault formation.
查看更多>>摘要：The viscosity of molten metals is a critical parameter influencing melt fluidity,alloy forming quality,and casting performance.It is therefore essential to maintain melt viscosity within an optimal range to enhance the fluidity and mold-filling capacity of molten metals.However,acquiring accurate data on liquid metal viscosity poses significant challenges due to the measurement difficulties and uncertainties in verifying the accuracy of theoretical calculations,hindering in-depth viscosity research.In this review,a systematic introduction of experimental methods for viscosity measurement and theoretical models for viscosity prediction was first conducted,together with an analysis on the advantages/disadvantages of each method/model.Then,all the experimental melt viscosities in unary,binary,ternary,and multi-component systems of light alloys especially aluminum alloys were summarized,and employed to verify the prediction accuracy of different theoretical models,ranging from physical,empirical,to geometrical ones.A comprehensive comparison between the predicted viscosities due to the theoretical model and the experimental data indicated that the CALPHAD approach and the machine learning method should be an effective strategy for predicting accurate viscosities in target alloy melts.Finally,the conclusions were drawn,and the future development directions for efficiently acquiring accurate viscosities in target alloy melts were also pointed out.
查看更多>>摘要：Cellular materials are gaining significant attention in product development due to their unique character-istics,offering superior mechanical performance and functionalities while minimizing material usage and environmental impact.This review article provides an overview of additive manufacturing(AM)technolo-gies for producing aluminum-based cellular materials,focusing on laser AM techniques including laser powder bed fusion and directed energy deposition.The article explores the classification of cellular mate-rials into stochastic foams and nonstochastic lattice structures and discusses conventional manufacturing methods and their limitations.It then examines the emergence of AM as a solution to these limitations,offering advantages such as design customization and optimization,shorter lead times,and the ability to manufacture complex architectures.The article highlights the current research status on AM of cellular materials including lattice shapes,design methods,and AM techniques.It further addresses the current status of AM of aluminum alloys,emphasizing the challenges and advances in producing aluminum-based cellular materials using AM.
查看更多>>摘要：A Ni-based solder BNi-5 was adopted as the repair agent to repair the prefabricated defects on the car-bon/carbon(C/C)composites.The effects of different heat-treatment(HT)temperatures and pre-oxidation on the chemical composition,microstructure,and mechanical behavior of the repaired C/C composites were investigated,and the repair mechanism was studied by finite element analysis methods.The repair agent and C/C composites were tightly bonded through mechanical interlocking and chemical reactions,and the flexural properties of the damaged C/C composites were significantly improved after repair.The products at the interface formed a gradient distribution structure of the thermal expansion coefficient when the HT temperature was 1300 ℃,which is beneficial to relieve the residual thermal stress at the interface.Meanwhile,the porosity of the surface of the C/C composites was higher after pre-oxidation,which led to more diffusion channels for the repair agent and enhanced the interface bonding ability.The flexural strength was the highest with a recovery rate of 85.2％when the C/C composites were pre-oxidized at 600 ℃ and the HT temperature was 1300 ℃.This work provides a strategy for the engineering application of the damage repair of C/C composites.
查看更多>>摘要：Magnesium matrix composites(MgMCs)have always suffered low strengthening efficiency and poor duc-tility due to the difficulties in pursuing the well-bonded interface.Herein,graphene nanoplatelets(GNPs)were decorated with magnesium oxide nanoparticles(MgO NPs)through chemical co-precipitation and then incorporated into AZ91 alloy to fabricate MgMCs via powder thixoforging.The effect of MgO on the interface of the Mg/graphene system was investigated based on the first-principles calculations,and the result indicated that modifying GNPs with MgO NPs was helpful in improving the Mg-GNP inter-face bonding.The interface structural analysis revealed that the MgO NPs were firmly bonded with both GNPs and α-Mg through the distortion area bonding and semi-coherent interfacial bonding,severing as a bridge to fasten the interface bonding of composites.In addition,the MgO NPs on GNPs acted as a barrier to prevent GNPs from seriously reacting with the AZ91 alloy.As a result,the AZ91/MgO@GNPs composite was endowed with enhancements of 31％and 10％in the yield strength,and increments of 71％and 61％in elongation compared with the AZ91 alloy and AZ91/GNPs composite,respectively,exhibiting a more significant potential in optimizing the strength-toughness tradeoff compared with the AZ91/GNPs.More-over,the possible strengthening and toughening mechanisms were also discussed in detail.This work offers a relatively novel surface modification strategy to modulate the Mg-GNP interface for a simultane-ous improvement of strength and ductility.
Chin Ho KirkPeikui WangChiang Yon Douglas ChongQi Zhao...
152-164页
查看更多>>摘要：TiO2 is one of the best-known environmentally friendly photocatalysts that has demonstrated the great potential to degrade a wide variety of organic foulants in water and wastewater treatment when placed under UV radiation.Currently,TiO2-based photocatalytic membranes are at the forefront of photodegra-dation research and technical readiness.The membrane setup provides a high contact surface area for ef-fective filtration and degradation,without the necessary hassle of photocatalyst recovery after water and wastewater treatment.Meanwhile,TiO2 photocatalytic ceramic membranes have become an emerging re-search area due to the inherent chemical and mechanical stability of ceramic membranes,which enables them to outperform polymeric membranes.With the recent shift from polymeric to ceramic membranes in industrial applications,TiO2 photocatalytic ceramic membranes will become a key player among the next-generation ceramic membranes,as they are capable of multiple functionalities.This review provides a timely and focused investigation into the fabrication and application of such TiO2 photocatalytic ceramic membranes for water and wastewater treatment.The benefits of using photocatalytic ceramic membranes in filtration,such as a higher foulant removal efficiency,higher water permeability,and much improved antifouling capabilities,are highlighted and explained.Finally,the current research,technical readiness,and remaining gaps are identified,and a set of critical insights are provided using the available data to guide the developmental pathway of practical TiO2 photocatalytic ceramic membranes for water and wastewater treatment.
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