查看更多>>摘要：The thermal simulation compression tests of near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe were per-formed within the range of deformation temperatures of 710-860 ℃ and strain rates of 0.001-1 s-1.Based on electron backscatter diffraction(EBSD)characterization and analysis technology,the inter-action between dynamic phase transformation(DPT)of β-to-α and dynamic recrystallization(DRX)under thermal-mechanical coupling is deeply and systematically explored.We clarify the effects of temperatures and strain rates on the orientation relationship during dynamic precipitation of α-phase within β grain interiors possessing special orientation.The results show that the intragranular α-phase precipitated on the subgrain boundaries near {001}β with a high degree of dynamic recovery(DRV)deviates more from Burgers Orientation Relationship(BOR)than the α-phase that precipitates near{111}βas temperature increases.The proportion of α-phase precipitated by strain-induced on β recrys-tallized equiaxed grains for the deviating angle from BOR(θBoR)in the range of 20°-30° increases to 40％with the increase of strain rates below 800 ℃.In addition,the α-phase is dynamically precipitated on the grain boundaries with {110}β orientation,which undergoes continuous dynamic recrystallization(CDRX),exhibiting epitaxial recrystallization,namely {110}β//{0001 }α.Furthermore,the morphology of grain boundaries α phase(αGBs)precipitated by strain-induced phase transformation(SIPT)on specific types of β grain boundaries(βGBs),as well as the crystallographic orientation relationship and variant selection effect between adjacent α-variant within β grains are elucidated.The orientation relationships between α variants in {111}β grain are related with each other by 50°-60°/<-12-10>and 60°-70°/<-48-43>rotation.The"necklace"αGBs of recrystallization exhibit mainly the rotation of 50°-70° around the<2-310>zone axis,while the adjacent α-variant in the grain interiors is mainly 60° or 90°/<12-30>.In summary,the study has contributed to a deeper understanding of the deformation behavior and DPT laws of β-to-αp in near-β titanium alloy,which lays a foundation for the optimization of the hot deformation process and mechanical properties.
查看更多>>摘要：Interfaces play a crucial role in influencing the mechanical properties of Mg alloys.For Mg-Li dual-phase alloy,the type of interfaces is complex,which includes both grain boundary and phase boundary,and the influence of such interfaces on the damage nucleation is yet to be explored.In this paper,in-situ scanning electron microscopy(SEM)based measurements were carried out to investigate the meso-scale damage nucleation mechanisms of the Mg-6Li dual-phase alloy.Results show that 94.8％of cracks are nucleated at the α-Mg grain boundary in the post-uniform elongation stage,while 5.2％are at phase boundary and almost no crack at the β-Li grain boundary.The initiation of α-Mg grain boundary cracks is attributed to strain incompatibility,which induces micro-strain localization,and then causes grain boundary sliding(GBS)and crack nucleation.Deformation compatibility analysis reveals that the geometric compatibility factor(Mk)can be used to predict the nucleation of α-Mg grain boundary crack.When Mk is lower than 0.075,α-Mg grain boundary cracks tend to form.Few cracks are generated at the phase boundary is due to the mild strain partitioning between α-Mg phase and β-Li phase and may also be partly attributed to multiple slip systems in body-centered cubic(BCC)-structured β-Li phase,which can accommodate well with the deformation of adjacent α-Mg phase.
查看更多>>摘要：Solidification cracking issues during additive manufacturing(AM)severely prevent the rapid development and broad application of this method.In this work,a representative Co34Cr32Ni27Al4Ti3 high-entropy al-loy(HEA)susceptible to crack formation was fabricated by selective laser melting(SLM).As expected,many macroscopic cracks appeared.The crack issues were successfully solved after introducing a certain amount of Fe-based metallic glass(MG)powder as a glue during SLM.The effect of MG addition on the formation and distribution of defects in the SLM-processed HEA was quantitatively investigated.With an increasing mass fraction of the MG,the dominant defects transformed from cracks to lack of fusion(LOF)defects and finally disappeared.Intriguingly,the MG preferred to be segregated to the boundaries of the molten pool.Moreover,the coarse columnar crystals gradually transformed into equiaxed crystals in the molten pool and fine-equiaxed crystals at the edge of the molten pool,inhibiting the initiation of cracks and providing extra grain boundary strengthening.Furthermore,multiple precipitates are formed at the boundaries of cellular structures,which contribute significantly to strengthening.Compared to the brit-tle SLM-processed Co34Cr32Ni27Al4Ti3 HEA,the SLM-processed HEA composite exhibited a high ultimate tensile strength greater than 1.4 Ga and enhanced elongation.This work demonstrates that adding Fe-based MG powders as glues into SLM-processed HEAs may be an attractive method to heal cracks and simultaneously enhance the mechanical properties of additively manufactured products.
查看更多>>摘要：The coupling of charge carrier and phonon transport limits the application of Ag2Se as a low-toxic near-room-temperature thermoelectric material.Strategies that reduce the thermal conductivity via enhanc-ing the phonon scattering usually lead to reduced carrier mobility due to high grain boundary potential barrier.In this study,we developed a cell-membrane-mimic grain boundary engineering strategy for de-coupling the charge carrier and phonon scattering through decorating high-dielectric-constant rutile TiO2 at Ag2Se grain boundaries to enable the charge carrier/phonon selective permeability.The nano-sized TiO2 with high dielectric permittivity can secure the charge carrier transport by shielding the interfacial Coulomb potential to lower the energy barrier of grain boundaries,rendering an enhanced power factor.Additionally,benefited from the enhanced phonon scattering by TiO2 nanoparticles,a significantly de-creased lattice thermal conductivity of～0.20 W m-1 K-1 and a high zT of～0.97 at 390 K are obtained in the Ag2Se-based nanocomposites.This work demonstrates that such cell-membrane-mimic grain bound-ary engineering strategy may shed light on developing high-performance thermoelectric materials.
查看更多>>摘要：SiBCN ceramic aerogel is an ideal potential candidate for ultra-high temperature thermal insulation due to its unique microscopic pore structure combined with the excellent thermal stability of SiBCN ce-ramic.Here,reduced graphene oxide(rGO)modified SiBCN aerogels(rGO/SiBCN)were prepared through solvothermal,freeze-casting and pyrolysis,and the dimension of the aerogel is up to Φ130 mm × 28 mm.The density of the rGO/SiBCN aerogel is as low as 0.024 g/cm3 and the microstructural regulation is achieved by controlling the rGO content in the aerogel.The hierarchical cellular structure endows the aerogel with a high specific surface area(148.6 m2/g)and low thermal conductivity(0.057 W m-1 K-1).The 10 mm-thick sample exhibits excellent thermal insulation and ablation resistance,as evidenced by its ability to reduce the temperature from～1100 ℃ to～180 ℃ under the intense heat of a butane flame.Moreover,benefiting from the ultrahigh-temperature stability of SiBCN,the rGO/SiBCN aerogel exhibits good thermal stability up to 1200 ℃ in argon and short-oxidation resistance at 800 ℃ in air.There-fore,the rGO/SiBCN aerogel with superior overall performance could expand its practical application in high-temperature thermal insulation under extreme environments.
查看更多>>摘要：Solar-driven selective upgrading of lignocellulosic biomass-derived alcohols to value-added chemicals and clean fuel hydrogen(H2)shows great potential for tackling the energy crisis and environmental pollu-tion issues.Here,we construct a MAPbBr3/ReS2 heterostructure by embedding distorted tetragonal(1T)phase ReS2 nanoflowers into large-sized MAPbBr3 for green value-added utilization of biomass-derived alcohols.The embedded structure effectively enlarges the contact interface between the ReS2 and the MAPbBr3,and importantly,induces a strong built-in electric field aligned between the spatially well-defined MAPbBr3 and ReS2 nanoflowers.Moreover,the distorted 1T phase ReS2 with low work function well matches the energy band of MAPbBr3,forming a heterostructure with a downward band bending at the interface.These features empower the MAPbBr3/ReS2 photocatalyst with high capability to promote charge separation and expedite the surface redox reaction.Consequently,optimal BAD and H2 production rates of about 1220 μmol h-1 g-1 are realized over a MAPbBr3/ReS2 2％sample,which are approximately 9 times greater than those of blank MAPbBr3.This work demonstrates the great potential of constructing an embedded transition metal dichalcogenide@metal halide perovskites heterostructure with downhill interfacial charge transfer for photocatalytic upgrading of biomass-derived alcohols.
查看更多>>摘要：Personal daytime radiative cooling(PDRC)materials have high sunlight reflection and high selective emis-sivity to outer space in the main atmospheric window,demonstrating huge potential in energy-saving for sustainable development.Recently,polymer-based membranes for radiative cooling have been widely re-ported,due to their easy processing,low cost,and unique optical performance.However,the desired high sunlight reflectance of PDRC materials is easily dampened by environmental aging,high temperature,and ultraviolet(UV)irradiation,resulting in reduced cooling performance for most polymers,adverse to large-scale practical applications.In this work,we demonstrate a novel polyimide nanofiber(PINF)membrane with a fluorine-containing structure via typical electrospinning technology.The resultant PINF membrane exhibits high sunlight reflectance,UV resistance,and excellent thermal stability,rendering anti-aging day-time radiative cooling.The sunlight reflectance of PINF membranes could maintain constant in the aging test for continuous 720 h under outdoor solar irradiation,exhibiting durable and long-term personal day-time radiative cooling performance.
查看更多>>摘要：Reducing the exploration of multi-principal element alloy space is a key challenge to design high-performance U-based high-entropy alloy(UHEA).Here,the best combination of multi-principal element can be efficiently acquired because proposed alloying strategy and screening criteria can substantially reduce the space of alloy and thus accelerate alloy design,rather than enormous random combinations through a trial-and-error approach.To choose the best seed alloy and suitable dopants,the screening criteria include small anisotropy,high specific modulus,high dynamical stability,and high ductility.We therefore find a shortcut to design UHEA from typical binary(UTi and UNb)to ternary(UTiNb),qua-ternary(UTiNbTa),and quinary(UTiNbTaFe).Finally,we find a best bcc senary UHEA(UTiNbTaFeMo),which has highest hardness and yield strength,while maintains good ductility among all the candidates.Compared to overestimation from empirical strength-hardness relationship,improved strength prediction can be achieved using a parameter-free theory considering volume mismatch and temperature effect on yield strength.This finding indicates that larger volume mismatch corresponds to higher yield strength,agreeing with the available measurements.Moreover,the dynamical stability and mechanical properties of candidates are greatly enhanced with increasing the number of multi-principal element,indicating the feasibility and effectiveness of adopted alloying strategy.The increasing of multi-principal element cor-responds to the increasing valence electron concentration(VEC).Alternatively,the mechanical properties significantly improve as increasing VEC,agreeing with measurements for other various bcc HEAs.This work can speed up research and development of advanced UHEA by greatly reducing the space of alloy composition.
查看更多>>摘要：The explosive growth of communication technology has given rise to a large number of high-quality electromagnetic wave(EMW)absorbing materials,and single-component materials are often difficult to satisfy the demand.In this study,we propose an etching method of molten chlorine salts under vac-uum to prepare Cl-terminated MXene(MX-Cl)which can meet the requirements of"thin,light,wide and strong"and realize the application of single-component absorbing materials.In the X and Ku bands,MX-Cl achieves a strong reflection loss of-42.99 dB and an effective absorption bandwidth of 3.44 GHz with the 1.2 mm matching thickness.The presence of Cl groups restricts the free electron movement of surface-Ti,which controls the conductivity of the MX-Cl and optimizes its permittivity.Dipole polarization induced by Ti-Cl,interfacial polarization between MXene layers and multiple scattering effects inside the layers all significantly increase the dielectric loss of the MX-Cl considerably.This study provides a new approach to investigating the effect of single atoms on the dielectric properties of materials.This work also offers a simple and low-cost process for the preparation of single-component MXene EMW-absorbing materials.
查看更多>>摘要：The photoabsorption capacity,the number of active sites,and the efficiency of carrier separation of photo-catalysts are the main factors that restrict photocatalytic activity.Accordingly,a series of novel CdO-based S-scheme photocatalysts are prepared by a facile one-step precipitation-calcination method for the first time.Although CdO with a narrow band gap has no photocatalytic hydrogen evolution performance,the CdMoO4/CdO composite exhibits excellent photocatalytic activity.The photocatalytic hydrogen evolution(PHE)performance of the optimal ratio(3∶4)is up to 7029 μmol g-1 h-1 under visible light irradiation.At the same time,the CdMoO4/CdO composite also shows excellent degradation activity of water pollu-tants,and the degradation efficiency for Tetracycline hydrochloride,Oxytetracycline,Norfloxacin,Reactive red 2,and Levofloxacin is 96.33％,95.38％,88.48％,95.93％,and 77.30％under visible light irradiation for 90min,respectively.According to the experimental characterization and theoretical calculation analysis,the introduction of CdMoO4 can be used to construct S-scheme heterojunction with CdO,improving the efficiency of charge separation as well as taking full advantage of redox ability,and hence improving su-perior photocatalysts performance.This work affords new insights into efficient PHE and antibiotic/dye degradation of CdO-based S-scheme photocatalysts.
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