A systematic understanding of the effect of magnetic field intensity on the liquid state-dependent solidi-fication of a Co-B hypereutectic alloy was carried out.The application of a magnetic field promotes nucleation,...A systematic understanding of the effect of magnetic field intensity on the liquid state-dependent solidi-fication of a Co-B hypereutectic alloy was carried out.The application of a magnetic field promotes nucleation,as evidenced by the reduction in undercooling,and the extent of the reduction is proportional to the intensity of the magnetic field.Nevertheless,for different liquid states,the magnetic field has dissimilar impacts on facilitating nucleation,manifested in the low-temperature liquid is more affected by the magnetic field,and the enhancing effect is more significant.A pre-nucleation model,modified from classical nucleation theory to include clusters as nucleation precursors,has been developed to describe the phenomena of liquid state-dependent nucleation.The model adeptly elucidates how the magnetic field intensity influences the nucleation of diverse melt structures differently,which is primarily attributed to the varying contact angles resulting from differences in surface tension as the magnetic field interacts with distinct melt structures.The present work might be helpful for not only theoretically understanding the effect of magnetic field intensity on the liquid state-dependent solidification but also providing an alternative strategy and criterion to tailor the microstructure and properties via magnetic field.展开更多
The structure transition inside the Co-81.5at.%B alloy liquid has been studied by an in-situ magnetization measurement.A crossover was observed on the 1/M-T curve during the overheating process,indicating that a liqui...The structure transition inside the Co-81.5at.%B alloy liquid has been studied by an in-situ magnetization measurement.A crossover was observed on the 1/M-T curve during the overheating process,indicating that a liquid-liquid structure transition(LLST)took place in the melt.Based on this information,the effects of LLST on the solidification behavior,microstructure and tribology property were investigated experimentally.The sample solidified with the LLST exhibits significantly different solidification behaviors,i.e.,the nucleation undercooling and the recalescence extent are conspicuously enlarged,and the solidification time is shortened.As a result,the microstructure is effectively refined and homogenized,and the hardness and wear resistance are significantly enhanced.The present work might be helpful for not only theoretically understanding the influence of LLST on the solidification behavior but also providing an alternative approach to tailor the microstructure and properties.展开更多
The effects of channel segregation on the macro-and micro-scale chemical composition,microstructure,hardness,and tensile deformation behavior of Ti45Nb wires were investigated.The results show that wires with severe c...The effects of channel segregation on the macro-and micro-scale chemical composition,microstructure,hardness,and tensile deformation behavior of Ti45Nb wires were investigated.The results show that wires with severe channel segregation exhibit a macroscopic chemical composition identical to those without segregation,and 3D X-ray imaging result also reveals no abnormalities.After annealing,both types of wires exhibit an equiaxed single-phase microstructure with comparable grain sizes,suggesting that channel segregation has negligible influence on the macroscopic composition and grain size.Metallographic examination reveals that channel segregation manifests as spot-like features in the transverse section and band-like structures in the longitudinal section.EDS analysis identifies these regions as Ti-enriched segregations,with a Ti content higher than that of the surrounding matrix by approximately 4.42wt%.Compared to segregation-free wires,those containing extensive channel segregation demonstrate a 15.5%increase in ultimate tensile strength and a 12.3%increase in yield strength,but suffer a reduction in elongation and reduction of area by 19.8%and 18.9%,respectively.Furthermore,the mechanical properties of wires with segregation show significant fluctuations.Fractographic analysis reveals a larger fracture surface area in segregated wires.Severe dislocation pile-ups occur at the interfaces of these segregated regions,initiating microcrack nucleation.This promotes rapid crack propagation of the Ti45Nb wire,leading to a significant decrease in plasticity and reduction of area.展开更多
Metal nanoclusters(MNCs),comprising several to hundreds of metal atoms,have attracted significant research interest owing to their distinctive physicochemical properties.Reticular frameworks(RFs)with ordered porous st...Metal nanoclusters(MNCs),comprising several to hundreds of metal atoms,have attracted significant research interest owing to their distinctive physicochemical properties.Reticular frameworks(RFs)with ordered porous structures,including metalorganic frameworks(MOFs),covalent organic frameworks(COFs),hydrogen-bonded organic frameworks(HOFs),and supramolecular organic frameworks(SOFs),possess a variety of unique properties due to their high crystallinity,high porosity,large surface area,and adjustable structure.The integration of MNCs with RFs endows the resulting composites with desirable features(e.g.,enhanced and tunable optical properties,improved catalytic and photophysical activities,selective molecular recognition),which facilitates a broad spectrum of biomedical applications and advancing the development of integrated theranostic nanoplatforms.This review summarizes recent advances in the synthesis and biomedical applications of various MNCs/RFs composites.We systematically categorize and evaluate key strategies for incorporating MNCs into four types of RFs(MOFs,COFs,HOFs,and SOFs)while discussing the advantages and limitations of each approach.The biomedical applications of these composites are comprehensively reviewed,encompassing biosensing,bioimaging,antitumor therapy,and antibacterial treatments.Finally,the review addresses current challenges and outlines future research directions,with the aim of guiding the rational design of novel MNCs/RFs composites,enabling precise control over their structures and functions toward advanced biomedical applications.展开更多
The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural ...The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural analysis,the welded joints exhibit distinct microstructural zones,including the stir zone(SZ),thermomechanically affected zone(TMAZ),and heat-affected zone(HAZ).The grain size of each zone is in the order of HAZ>TMAZ>SZ.Notably,the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ,with particle size in the HAZ increasing at higher rotational speeds.Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ>TMAZ>SZ>BM,with greater sensitivity observed at increased rotational speeds.Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps,but not from the changes in the microstructure.展开更多
Layered oxides present compelling potential as cathode materials for sodium-ion batteries(SIBs).However,challenges including interfacial instability and sluggish reaction kinetics critically limit their rate capabilit...Layered oxides present compelling potential as cathode materials for sodium-ion batteries(SIBs).However,challenges including interfacial instability and sluggish reaction kinetics critically limit their rate capability and cycling performance.Herein,we introduce the water-soluble sodium polyacrylate(NaPAA)binder as a promising approach to mitigating these issues in P2-type layered oxides.The NaPAA binder facilitates the formation of a uniform Na^(+) conductive interfacial film,which protects the cathode against electrolyte-induced corrosion and effectively inhibits the dissolution of transition metals in P2-Na_(0.85)Li_(0.12)Ni_(0.22)Mn_(0.66)O_(2)(NLNMO).Furthermore,we elucidate the mechanism by which the NaPAA binder dynamically regulates the coordination of free anions at the electrode-electrolyte interface.This regulation reduces solvent decomposition and promotes the formation of a stable,ionically conductive layer.Consequently,the P2-NLNMO@NaPAA integrated electrode exhibits enhanced electrochemical performance,achieving an 89.2%capacity retention after 200 cycles at 0.2 C and delivering an initial capacity of 102.9 mA h g^(-1) even at 0℃.This study advances the fundamental understanding of binder-mediated interface engineering and demonstrates a scalable and eco-friendly manufacturing pathway for high-performance SIBs.展开更多
In order to overcome the embrittlement of metastable titanium alloys caused by the precipitation ofωiso phase during aging,regulation of isothermalωprecipitation was investigated in Ti−15Mo alloy.The results show th...In order to overcome the embrittlement of metastable titanium alloys caused by the precipitation ofωiso phase during aging,regulation of isothermalωprecipitation was investigated in Ti−15Mo alloy.The results show that the sample is brittle when direct aging(A)is applied at 350℃for 1 h after solution treatment(ST).If pre-deformation(D)is performed on the ST sample to induce{332}twins and secondaryα″phase,subsequent aging at 350℃(STDA350)improves the strength to 931 MPa with a good ductility of about 20%maintained.However,when aging is performed at 400℃or 450℃(STDA400/450),the strength can be further improved,but the ductility is dramatically reduced.Atomic-scale characterizations show that the partial collapse ofωphase in the STDA350 sample effectively eliminates aging-induced embrittlement,but complete collapse leads to poor ductility in the STDA400/450 sample.展开更多
Exploring the influence of the coordination environment of single-atom catalysts(SACs)on the electrochemical CO_(2)reduction reaction is vital for assessing the reaction mechanism and structure-performance relationshi...Exploring the influence of the coordination environment of single-atom catalysts(SACs)on the electrochemical CO_(2)reduction reaction is vital for assessing the reaction mechanism and structure-performance relationship.However,it is challenging to engineer the coordination configuration of isolated active metal atoms precisely.Herein,we strategically manipulate the coordination number of the Co-N_(x) configuration by simply changing the order of adding the metal precursor toward improved CO_(2)electrolysis performance.Compared with the symmetric Co-N_(4)coordination,the asymmetric Co-N_(3)coordination leads to reinforced Co-N interaction and downshifted 3d orbital energy toward the Fermi level of the active Co sites,promoting the activation of CO_(2)molecules and the formation of critical intermediate^(*)COOH.The as-designed Co-N_(3)SAC displays excellent Faradaic efficiency(FE)of 98.4%for CO_(2)-to-CO conversion at a low potential of-0.80 V,together with decent FE over a wide potential range(-0.50 V to-1.10 V)and high durability.This study presents an ideal platform to manipulate the coordination number of atomically dispersed metal catalysts and provides a fundamental understanding of coordination configurationperformance correlation for CO_(2)electroreduction.展开更多
In this study, the phase field method was used to study the multi-controlling factors of dendrite growth in directional solidification. The effects of temperature gradient, propelling velocity, thermal disturbance and...In this study, the phase field method was used to study the multi-controlling factors of dendrite growth in directional solidification. The effects of temperature gradient, propelling velocity, thermal disturbance and growth orientation angle on the growth morphology of the dendritic growth in the solid/liquid interface were discussed. It is found that the redistribution of solute leads to multilevel cavity and multilevel fusion to form multistage solute segregation, and the increase of temperature gradient and propelling velocity can accelerate the dendrite growth of directional solidification, and also make the second dendrites more developed, which reduces the primary distance and the solute segregation. When the temperature gradient is large, the solid-liquid interface will move forward in a flat interface mode,and the thermal disturbance does not affect the steady state behavior of the directionally solidified dendrite tip. It only promotes the generation and growth of the second dendrites and forms the asymmetric dendrite. Meanwhile, it is found that the inclined dendrite is at a disadvantage in the competitive growth compared to the normal dendrite, and generally it will disappear. When the inclination angle is large, the initial primary dendrite may be eliminated by its secondary or third dendrite.展开更多
In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium a...In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium alloy ingots during VAR process.The results show that the temperature fields obtained by the simulation are well validated through the experiment results.The temperature distribution is different during the whole VAR process and the steady-state molten pool forms at 329 s for d100 mm × 180 mm ingots.At the initial stage of remelting,the heat dissipation of crucible bottom plays an important role in the whole heat dissipation system.At the middle of remelting,the crucible wall becomes a major heat dissipation way.The effect of cooling velocity on the solidification structure of ingots was investigated based on the temperature fields and the results can well explain the macrostructure of titanium alloy ingots.展开更多
The influence of melt superheating treatment on the solid/liquid （S/L） interface morphology of directionally solidified Ni-based superalloy DZ125 is investigated to elucidate the relationship between melt characteri...The influence of melt superheating treatment on the solid/liquid （S/L） interface morphology of directionally solidified Ni-based superalloy DZ125 is investigated to elucidate the relationship between melt characteristic and S/L interface stability. The results indicate that the interface morphology is not only related to the withdrawal velocity （R） but also to the melt superheating temperature （Ts） when the thermal gradient of solidification interface remains constant for different Ts with appropriate superheating treatment regulation. The interface morphology changes from cell to plane at R of 1.1 μm/s when Ts increases from 1500°C to 1650°C, and maintains plane with further elevated Ts of 1750°C. However, the interface morphology changes from coarse dendrite to cell and then to cellular dendrite at R of 2.25 μm/s when Ts increases from 1500°C to 1650°C and then to 1750°C. It is proved that the solidification onset temperature and the solidification interval undergo the nonlinear variation when Ts increases from 1500°C to 1680°C, and the turning point is 1650°C at which the solidification onset temperature and the solidification interval are all minimum. This indicates that the melt superheating treatment enhances the solidification interface stability and has important effect on the solidification characteristics.展开更多
The effects of solute elements during solidification on the grain size are very important and can be quantified by the growth-restriction parameter Q,and Q possesses the better correlation with the grain size. Based o...The effects of solute elements during solidification on the grain size are very important and can be quantified by the growth-restriction parameter Q,and Q possesses the better correlation with the grain size. Based on the constitutional undercooling generated by the growth of an adjacent grain during the initial solidification,the growth-restriction parameter Q is deduced and a comprehensive physical basis of Q is obtained by using an initial solute distributing equation. For the alloys with more potent nucleants,Q is a suitable predictor of the grain size. For less potent nucleants,the relative grain size(RGS) is a more accurate prediction of the grain size. This prediction coincides with the experimental behaviors for Al-Ti and Al-Cu alloys with lower solute content.展开更多
The effect of A1 content on the microstructure and solidification characteristics of Ti-A1-Nb-V-Cr alloys in as-cast and isothermally treated states was investigated using X-ray diffraction （XRD）, scanning electron ...The effect of A1 content on the microstructure and solidification characteristics of Ti-A1-Nb-V-Cr alloys in as-cast and isothermally treated states was investigated using X-ray diffraction （XRD）, scanning electron microscopy （SEM） equipped with energy dispersive spectroscope （EDS）, and transmission electron microscopy （TEM）. The typical solidification characteristics are due to the joint influence of both the crystal temperature range and the solidification path. The wide crystallization temperature range contributes to obtaining coarse dendrites in the as-cast Ti47A17Nb2.5V1.0Cr （at%） alloy solidifying through the peritectic reaction. The β-solidifying Ti46A17Nb2.5V1.0Cr （at%） alloy with the narrow crystallization temperature range is attributed to the formation of a homogeneous finegrained microstructure. However, the crystallization temperature range of Ti48A17Nb2.5V1.0Cr （at%） alloy is equivalent to that of Ti46A17Nb2.5V1.0Cr alloy, but it is solidified by peritectic reaction, leading to the formation of finer dendrites.展开更多
Laser directed energy deposition(DED)involves complex physical processes,and the trial and error examinations are time consuming and cost expensive.The research paradigm can be reshaped using advanced phenomenological...Laser directed energy deposition(DED)involves complex physical processes,and the trial and error examinations are time consuming and cost expensive.The research paradigm can be reshaped using advanced phenomenological models via computing the spatiotemporal variations of the build features.In this work,multi-layer and multi-track laser DED of Ti-6 Al-4 V were systematically explored on multiple scales including the 1D track,the 2D layer and the 3D full build considering the complex transport of energy,mass,and momentum in the moving freeform molten pool.The results showed that convex,nearflat,and wavy builds were generated using gradually larger hatch spacings.The profiles of individual tracks and layers were extracted through the unique advantages of the model.The individual tracks exhibited various patterns and rotated with specific inclinations to form distinct layer profiles.The net increments of the deposit generated upon the printing of a new track during the continuous deposition process showed that the smaller hatch spacing caused higher overlap rate of horizontally adjacent tracks but lower remelting rate of vertically adjacent tracks in neighboring layers.The 3D numerical model was validated with corresponding experiments for various process conditions.The scientific findings can provide useful insights for further researches of DED.展开更多
The homogeneous liquid was separated into two phases, （Fe, Co）-rich LI and Cu-rich L2, once the melt was undercooled below a liquid-phase separation temperature Tsep. If the duration from Tsep to Tsl （solidificatio...The homogeneous liquid was separated into two phases, （Fe, Co）-rich LI and Cu-rich L2, once the melt was undercooled below a liquid-phase separation temperature Tsep. If the duration from Tsep to Tsl （solidification temperature of LI phase）, termed the liquid-phase separation interval Δt, exceeded a critical value, an eggtype structure was observed. By utilizing differential thermal analyses （DTA）, the solidification process of the undercooled Fe-Co-Cu alloys was studied. Additionally, an immiscible boundary was obtained, which was a convex parabola with a symmetrical axis of XCu=0.52. Depending on the relative amounts of LI and L2, the minor phase was nucleated firstly to form liquid droplets and separated from the original liquids at the beginning of liquid-phase separation.展开更多
Phase selection and growth characteristics of directionally solidified Al_(2)O_(3)/GdAlO_3(GAP)faceted eutectic ce ramics are investigated over wide ranges of compositions and solidification rates to explore the eutec...Phase selection and growth characteristics of directionally solidified Al_(2)O_(3)/GdAlO_3(GAP)faceted eutectic ce ramics are investigated over wide ranges of compositions and solidification rates to explore the eutectic coupled zone.Through the obse rvation of the quenched solid-liquid interface,the competitive growth of primary faceted Al_(2)O_(3)phase,prima ry non-faceted GAP phase and Al_(2)O_(3)/GAP eutectic with diffe rent morphologies is detected.Microstructure transitions from wholly eutectic to primary Al_(2)O_(3)(GAP)dendrite plus eutectic and then to wholly eutectic are found in Al_(2)O_(3)-2 O mol%Gd_(2)O_(3)hypoeutectic(Al_(2)O_(3)-26 mol%Gd_(2)O_(3)hypereutectic)ceramics with the increase of solidification rate.The dendrite growth of faceted Al_(2)O_(3)and non-faceted GAP phases are well predicted by KGT model,which have introduced appro p riate dimensionless supersaturationΩto characterize the anisotropic growth of dendrites.Based on the maximum interface temperature criterion,the competitive growth of primary phase and eutectic is analyzed theoretically and the predicted coupled zone of Al_(2)O_(3)/GAP eutectic ceramics is in good agreement with the experimental results.Besides,the influence of microstructure with these different morphologies on the flexural strength of Al_(2)O_(3)/GAP eutectic ceramics is studied.展开更多
Rapid surface resolidification with a high powered CO2-laser was performed in preparing directionally solidified Al2O3/YAG/ZrO2 ternary eutectic ceramic in situ composite.The effects of laser processing parameters on ...Rapid surface resolidification with a high powered CO2-laser was performed in preparing directionally solidified Al2O3/YAG/ZrO2 ternary eutectic ceramic in situ composite.The effects of laser processing parameters on the solidification microstructure characteristics and thermal properties were studied by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),X-ray diffractometry(XRD)and synthetically thermal analysis(STA).Detailed investigations of the influence of laser power and scanning rate on the preparation and microstructural parameters of the ternary eutectic were presented.Moreover, the eutectic phase separation rule at high temperature was discussed.The results indicate that solidification microstructure of the ternary eutectic composite is greatly influenced by the laser processing parameters.The synthetically thermal analysis shows that the eutectic temperature of ternary Al2O3/YAG/ZrO2 composite is 1 738℃,well matching the phase diagram of Al2O3-Y2O3-ZrO2.展开更多
Due to the effective precipitation strengthening effect of the β phase, Mg-Gd alloys exhibit excellent room temperature mechanical behaviors. However, when served at high temperatures, the metastable β phase will tr...Due to the effective precipitation strengthening effect of the β phase, Mg-Gd alloys exhibit excellent room temperature mechanical behaviors. However, when served at high temperatures, the metastable β phase will transform to other phases, resulting in severe performance degradation. In this study, we investigated the effect of precipitation state achieved by different heat treatments on high temperature tensile and creep behaviors of the Mg-15Gd alloy by comparing the properties of the as-cast, solid-solutioned(T4) and peak-aged(T6) alloys. The results showed that the tensile mechanical properties of the T6 alloy were always highest from room temperature to 300 ℃, in spite of an abnormal strength increase with temperature existed in the T4 alloy. For tensile creep properties, the T6 alloy exhibited the lowest steady creep rate below 235 ℃ while the T4 alloy possessed the best properties above 260 ℃. Microstructure characterization revealed that the transition was caused by the stress-promoted precipitation of β phase in the T4 alloy and rapid phase transformation in the T6 alloy at high temperatures. At 260 ℃, the calculated stress exponent n was 3.1 and 2.8 for the T4 and T6 alloys, respectively, suggesting the creep deformation mechanism was dislocation slip, which was further confirmed by the microstructure after creeping. Our findings can provide new insights into the heat treatment process of Mg-Gd alloys served at high temperatures.展开更多
Solidification behaviour of AA8006 aluminium alloy in suction casting has been investigated by field emission scanning electron microscopy with energy dispersive spectroscopy （EDS）. It is found that there is a secon...Solidification behaviour of AA8006 aluminium alloy in suction casting has been investigated by field emission scanning electron microscopy with energy dispersive spectroscopy （EDS）. It is found that there is a secondary solidification process of the remaining liquid in located region of α-Al dendrites, and the cooling rate influences not only the solidification of the primary α-Al dendrite, but also the secondary solidification process of the remaining liquid. With the primary solidification being responsible for the formation of the relatively large α- Al dendrite, a fine and homogeneous microstructure is observed in the secondary solidification. Furthermore, because of the presence of the fine microstructure, the eutectic reaction is confined into small intergranular areas, inducing the formation of the laminar eutectic phase in the primary solidification region and fibrous eutectic phase in the secondary solidification region. EDS analysis shows that the content of Fe is higher in the secondary solidification region, and the enrichment of the solute element further confirms the existence of the secondary solidification.展开更多
A single crystal Ni-based superalloy AM3 was processed at withdraw rates of 3.5, 10, 50, 100, 200, and 500 μm·s-1, respectively.The as-cast microstructures and solidification segregation ratio were characterized...A single crystal Ni-based superalloy AM3 was processed at withdraw rates of 3.5, 10, 50, 100, 200, and 500 μm·s-1, respectively.The as-cast microstructures and solidification segregation ratio were characterized with various withdraw rates.The shape and size of carbide microstructures were determined.As expected, the primary and secondary dendrite arm spacings (PDAS and SDAS) decrease with the increase of withdraw rate.The highest volume fraction of eutectic γ/γ' is observed at the 100 μm·s-1 withdraw rate.The volume fraction of eutectic γ/γ' does not appear to be a strong function of the withdraw rate.With increasing withdraw rate, interface morphologies change in the sequence of planar, cellular, and dendrite.There is a general refinement of the microstructure as the withdraw rate increases.EPMA analysis showed that withdraw rate does not have obvious influence on the segregation of elements.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52104386 and 52127807)the State Key Laboratory of Solidification Processing(NPU),China(Nos.2024-ZD-02 and 2024-BJ-02).
文摘A systematic understanding of the effect of magnetic field intensity on the liquid state-dependent solidi-fication of a Co-B hypereutectic alloy was carried out.The application of a magnetic field promotes nucleation,as evidenced by the reduction in undercooling,and the extent of the reduction is proportional to the intensity of the magnetic field.Nevertheless,for different liquid states,the magnetic field has dissimilar impacts on facilitating nucleation,manifested in the low-temperature liquid is more affected by the magnetic field,and the enhancing effect is more significant.A pre-nucleation model,modified from classical nucleation theory to include clusters as nucleation precursors,has been developed to describe the phenomena of liquid state-dependent nucleation.The model adeptly elucidates how the magnetic field intensity influences the nucleation of diverse melt structures differently,which is primarily attributed to the varying contact angles resulting from differences in surface tension as the magnetic field interacts with distinct melt structures.The present work might be helpful for not only theoretically understanding the effect of magnetic field intensity on the liquid state-dependent solidification but also providing an alternative strategy and criterion to tailor the microstructure and properties via magnetic field.
基金financially supported by the fund of National Key Laboratory for Precision Hot Processing of Metals(No.6142909200104)Shanghai Sailing Program+2 种基金National Training Program of Innovation and Entrepreneurship for Undergraduates(No.S202010699137)Natural Science Foundation of China(Nos.51690164 and 51801161)the Fundamental Research Funds for the Central Universities。
文摘The structure transition inside the Co-81.5at.%B alloy liquid has been studied by an in-situ magnetization measurement.A crossover was observed on the 1/M-T curve during the overheating process,indicating that a liquid-liquid structure transition(LLST)took place in the melt.Based on this information,the effects of LLST on the solidification behavior,microstructure and tribology property were investigated experimentally.The sample solidified with the LLST exhibits significantly different solidification behaviors,i.e.,the nucleation undercooling and the recalescence extent are conspicuously enlarged,and the solidification time is shortened.As a result,the microstructure is effectively refined and homogenized,and the hardness and wear resistance are significantly enhanced.The present work might be helpful for not only theoretically understanding the influence of LLST on the solidification behavior but also providing an alternative approach to tailor the microstructure and properties.
基金National Natural Science Foundation of China(U24A2038)。
文摘The effects of channel segregation on the macro-and micro-scale chemical composition,microstructure,hardness,and tensile deformation behavior of Ti45Nb wires were investigated.The results show that wires with severe channel segregation exhibit a macroscopic chemical composition identical to those without segregation,and 3D X-ray imaging result also reveals no abnormalities.After annealing,both types of wires exhibit an equiaxed single-phase microstructure with comparable grain sizes,suggesting that channel segregation has negligible influence on the macroscopic composition and grain size.Metallographic examination reveals that channel segregation manifests as spot-like features in the transverse section and band-like structures in the longitudinal section.EDS analysis identifies these regions as Ti-enriched segregations,with a Ti content higher than that of the surrounding matrix by approximately 4.42wt%.Compared to segregation-free wires,those containing extensive channel segregation demonstrate a 15.5%increase in ultimate tensile strength and a 12.3%increase in yield strength,but suffer a reduction in elongation and reduction of area by 19.8%and 18.9%,respectively.Furthermore,the mechanical properties of wires with segregation show significant fluctuations.Fractographic analysis reveals a larger fracture surface area in segregated wires.Severe dislocation pile-ups occur at the interfaces of these segregated regions,initiating microcrack nucleation.This promotes rapid crack propagation of the Ti45Nb wire,leading to a significant decrease in plasticity and reduction of area.
基金supported by the National Natural Science Foundation of China(Nos.U213010103,22274131).
文摘Metal nanoclusters(MNCs),comprising several to hundreds of metal atoms,have attracted significant research interest owing to their distinctive physicochemical properties.Reticular frameworks(RFs)with ordered porous structures,including metalorganic frameworks(MOFs),covalent organic frameworks(COFs),hydrogen-bonded organic frameworks(HOFs),and supramolecular organic frameworks(SOFs),possess a variety of unique properties due to their high crystallinity,high porosity,large surface area,and adjustable structure.The integration of MNCs with RFs endows the resulting composites with desirable features(e.g.,enhanced and tunable optical properties,improved catalytic and photophysical activities,selective molecular recognition),which facilitates a broad spectrum of biomedical applications and advancing the development of integrated theranostic nanoplatforms.This review summarizes recent advances in the synthesis and biomedical applications of various MNCs/RFs composites.We systematically categorize and evaluate key strategies for incorporating MNCs into four types of RFs(MOFs,COFs,HOFs,and SOFs)while discussing the advantages and limitations of each approach.The biomedical applications of these composites are comprehensively reviewed,encompassing biosensing,bioimaging,antitumor therapy,and antibacterial treatments.Finally,the review addresses current challenges and outlines future research directions,with the aim of guiding the rational design of novel MNCs/RFs composites,enabling precise control over their structures and functions toward advanced biomedical applications.
基金supported by the National Natural Science Foundation of China (Nos. 52075449, 51975480)。
文摘The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural analysis,the welded joints exhibit distinct microstructural zones,including the stir zone(SZ),thermomechanically affected zone(TMAZ),and heat-affected zone(HAZ).The grain size of each zone is in the order of HAZ>TMAZ>SZ.Notably,the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ,with particle size in the HAZ increasing at higher rotational speeds.Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ>TMAZ>SZ>BM,with greater sensitivity observed at increased rotational speeds.Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps,but not from the changes in the microstructure.
基金supported by the National Natural Science Foundation of China(52374311)National Key R&D Program of China(2023YFE0203000)+3 种基金the National Natural Science Foundation of Shaanxi(2023KXJ-262,2025SYS-SYSZD-035)the Fund of the State Key Laboratory of Solidification Processing in NPU(2025-TS-10)the Fundamental Research Funds for the Central Universities(D5000250277)the Youth Innovation Team of Shaanxi Universities。
文摘Layered oxides present compelling potential as cathode materials for sodium-ion batteries(SIBs).However,challenges including interfacial instability and sluggish reaction kinetics critically limit their rate capability and cycling performance.Herein,we introduce the water-soluble sodium polyacrylate(NaPAA)binder as a promising approach to mitigating these issues in P2-type layered oxides.The NaPAA binder facilitates the formation of a uniform Na^(+) conductive interfacial film,which protects the cathode against electrolyte-induced corrosion and effectively inhibits the dissolution of transition metals in P2-Na_(0.85)Li_(0.12)Ni_(0.22)Mn_(0.66)O_(2)(NLNMO).Furthermore,we elucidate the mechanism by which the NaPAA binder dynamically regulates the coordination of free anions at the electrode-electrolyte interface.This regulation reduces solvent decomposition and promotes the formation of a stable,ionically conductive layer.Consequently,the P2-NLNMO@NaPAA integrated electrode exhibits enhanced electrochemical performance,achieving an 89.2%capacity retention after 200 cycles at 0.2 C and delivering an initial capacity of 102.9 mA h g^(-1) even at 0℃.This study advances the fundamental understanding of binder-mediated interface engineering and demonstrates a scalable and eco-friendly manufacturing pathway for high-performance SIBs.
基金the financial support from the National Natural Science Foundation of China (No. 52374380)the China Postdoctoral Science Foundation (Nos. 2023M730234, 2024T171126)。
文摘In order to overcome the embrittlement of metastable titanium alloys caused by the precipitation ofωiso phase during aging,regulation of isothermalωprecipitation was investigated in Ti−15Mo alloy.The results show that the sample is brittle when direct aging(A)is applied at 350℃for 1 h after solution treatment(ST).If pre-deformation(D)is performed on the ST sample to induce{332}twins and secondaryα″phase,subsequent aging at 350℃(STDA350)improves the strength to 931 MPa with a good ductility of about 20%maintained.However,when aging is performed at 400℃or 450℃(STDA400/450),the strength can be further improved,but the ductility is dramatically reduced.Atomic-scale characterizations show that the partial collapse ofωphase in the STDA350 sample effectively eliminates aging-induced embrittlement,but complete collapse leads to poor ductility in the STDA400/450 sample.
基金financially supported by the Program for the Development of Science and Technology of Jilin Province(No.20240101004JJ)the National Natural Science Foundation of China(No.22409165)+4 种基金the National Foreign Experts Program of the Ministry of Human Resources and Social Security(No.Y20240003)the Shaanxi Province Talent Programfinancially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Nos.XDB0600000,XDB0600100,XDB0600200,XDB0600300,XDB0600400)Liaoning Binhai Laboratory(No.LILBLB-2023-04)Dalian Revitalization Talents Program(No.2022RG01)。
文摘Exploring the influence of the coordination environment of single-atom catalysts(SACs)on the electrochemical CO_(2)reduction reaction is vital for assessing the reaction mechanism and structure-performance relationship.However,it is challenging to engineer the coordination configuration of isolated active metal atoms precisely.Herein,we strategically manipulate the coordination number of the Co-N_(x) configuration by simply changing the order of adding the metal precursor toward improved CO_(2)electrolysis performance.Compared with the symmetric Co-N_(4)coordination,the asymmetric Co-N_(3)coordination leads to reinforced Co-N interaction and downshifted 3d orbital energy toward the Fermi level of the active Co sites,promoting the activation of CO_(2)molecules and the formation of critical intermediate^(*)COOH.The as-designed Co-N_(3)SAC displays excellent Faradaic efficiency(FE)of 98.4%for CO_(2)-to-CO conversion at a low potential of-0.80 V,together with decent FE over a wide potential range(-0.50 V to-1.10 V)and high durability.This study presents an ideal platform to manipulate the coordination number of atomically dispersed metal catalysts and provides a fundamental understanding of coordination configurationperformance correlation for CO_(2)electroreduction.
基金financially supported by the National Natural Science Foundation of China(NSFC)under grant Nos.51774254,51774253,U1610123,51574207,51574206the Science and Technology Major Project of Shanxi Province under grant No.MC2016-06
文摘In this study, the phase field method was used to study the multi-controlling factors of dendrite growth in directional solidification. The effects of temperature gradient, propelling velocity, thermal disturbance and growth orientation angle on the growth morphology of the dendritic growth in the solid/liquid interface were discussed. It is found that the redistribution of solute leads to multilevel cavity and multilevel fusion to form multistage solute segregation, and the increase of temperature gradient and propelling velocity can accelerate the dendrite growth of directional solidification, and also make the second dendrites more developed, which reduces the primary distance and the solute segregation. When the temperature gradient is large, the solid-liquid interface will move forward in a flat interface mode,and the thermal disturbance does not affect the steady state behavior of the directionally solidified dendrite tip. It only promotes the generation and growth of the second dendrites and forms the asymmetric dendrite. Meanwhile, it is found that the inclined dendrite is at a disadvantage in the competitive growth compared to the normal dendrite, and generally it will disappear. When the inclination angle is large, the initial primary dendrite may be eliminated by its secondary or third dendrite.
基金Project(2007CB613802) supported by the National Basic Research Program of China
文摘In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium alloy ingots during VAR process.The results show that the temperature fields obtained by the simulation are well validated through the experiment results.The temperature distribution is different during the whole VAR process and the steady-state molten pool forms at 329 s for d100 mm × 180 mm ingots.At the initial stage of remelting,the heat dissipation of crucible bottom plays an important role in the whole heat dissipation system.At the middle of remelting,the crucible wall becomes a major heat dissipation way.The effect of cooling velocity on the solidification structure of ingots was investigated based on the temperature fields and the results can well explain the macrostructure of titanium alloy ingots.
基金supports from the National Natural Science Foundation of China (Grant No. 50931004)the National Basic Research Program of China (Grant Nos. 2011CB610406 and 2010CB631202)the National High Technology Research and Development Program (Grant No. 2007AA03Z552)
文摘The influence of melt superheating treatment on the solid/liquid （S/L） interface morphology of directionally solidified Ni-based superalloy DZ125 is investigated to elucidate the relationship between melt characteristic and S/L interface stability. The results indicate that the interface morphology is not only related to the withdrawal velocity （R） but also to the melt superheating temperature （Ts） when the thermal gradient of solidification interface remains constant for different Ts with appropriate superheating treatment regulation. The interface morphology changes from cell to plane at R of 1.1 μm/s when Ts increases from 1500°C to 1650°C, and maintains plane with further elevated Ts of 1750°C. However, the interface morphology changes from coarse dendrite to cell and then to cellular dendrite at R of 2.25 μm/s when Ts increases from 1500°C to 1650°C and then to 1750°C. It is proved that the solidification onset temperature and the solidification interval undergo the nonlinear variation when Ts increases from 1500°C to 1680°C, and the turning point is 1650°C at which the solidification onset temperature and the solidification interval are all minimum. This indicates that the melt superheating treatment enhances the solidification interface stability and has important effect on the solidification characteristics.
基金Project(G2000067202-1) supported by the National Basic Research Program of China
文摘The effects of solute elements during solidification on the grain size are very important and can be quantified by the growth-restriction parameter Q,and Q possesses the better correlation with the grain size. Based on the constitutional undercooling generated by the growth of an adjacent grain during the initial solidification,the growth-restriction parameter Q is deduced and a comprehensive physical basis of Q is obtained by using an initial solute distributing equation. For the alloys with more potent nucleants,Q is a suitable predictor of the grain size. For less potent nucleants,the relative grain size(RGS) is a more accurate prediction of the grain size. This prediction coincides with the experimental behaviors for Al-Ti and Al-Cu alloys with lower solute content.
基金financially supported by the National Basic Research Program of China(No.2011CB605503)the Program of Introducing Talents of Discipline to Universities(No.B08040)
文摘The effect of A1 content on the microstructure and solidification characteristics of Ti-A1-Nb-V-Cr alloys in as-cast and isothermally treated states was investigated using X-ray diffraction （XRD）, scanning electron microscopy （SEM） equipped with energy dispersive spectroscope （EDS）, and transmission electron microscopy （TEM）. The typical solidification characteristics are due to the joint influence of both the crystal temperature range and the solidification path. The wide crystallization temperature range contributes to obtaining coarse dendrites in the as-cast Ti47A17Nb2.5V1.0Cr （at%） alloy solidifying through the peritectic reaction. The β-solidifying Ti46A17Nb2.5V1.0Cr （at%） alloy with the narrow crystallization temperature range is attributed to the formation of a homogeneous finegrained microstructure. However, the crystallization temperature range of Ti48A17Nb2.5V1.0Cr （at%） alloy is equivalent to that of Ti46A17Nb2.5V1.0Cr alloy, but it is solidified by peritectic reaction, leading to the formation of finer dendrites.
基金The National Key Research and Development Program of China(No.2017YFB1103000)The National Natural Science Foundation of China(No.51805267)+1 种基金The Natural Science Foundation of Jiangsu Province(No.BK20180483)the fund of the State Key Laboratory of Solidification Processing in NWPU(No.SKLSP201830)。
文摘Laser directed energy deposition(DED)involves complex physical processes,and the trial and error examinations are time consuming and cost expensive.The research paradigm can be reshaped using advanced phenomenological models via computing the spatiotemporal variations of the build features.In this work,multi-layer and multi-track laser DED of Ti-6 Al-4 V were systematically explored on multiple scales including the 1D track,the 2D layer and the 3D full build considering the complex transport of energy,mass,and momentum in the moving freeform molten pool.The results showed that convex,nearflat,and wavy builds were generated using gradually larger hatch spacings.The profiles of individual tracks and layers were extracted through the unique advantages of the model.The individual tracks exhibited various patterns and rotated with specific inclinations to form distinct layer profiles.The net increments of the deposit generated upon the printing of a new track during the continuous deposition process showed that the smaller hatch spacing caused higher overlap rate of horizontally adjacent tracks but lower remelting rate of vertically adjacent tracks in neighboring layers.The 3D numerical model was validated with corresponding experiments for various process conditions.The scientific findings can provide useful insights for further researches of DED.
基金supported by the Natural Science Foundation of China (Grant No.50771084)the Natural Science Foundation of the Education Department of Jiangsu province,China (Grant No.09KJB430004)
文摘The homogeneous liquid was separated into two phases, （Fe, Co）-rich LI and Cu-rich L2, once the melt was undercooled below a liquid-phase separation temperature Tsep. If the duration from Tsep to Tsl （solidification temperature of LI phase）, termed the liquid-phase separation interval Δt, exceeded a critical value, an eggtype structure was observed. By utilizing differential thermal analyses （DTA）, the solidification process of the undercooled Fe-Co-Cu alloys was studied. Additionally, an immiscible boundary was obtained, which was a convex parabola with a symmetrical axis of XCu=0.52. Depending on the relative amounts of LI and L2, the minor phase was nucleated firstly to form liquid droplets and separated from the original liquids at the beginning of liquid-phase separation.
基金supported financially by the National Natural Science Foundation of China(Nos.51822405 and 51472200)the National Key R&D Program of China(Nos.2017YFB1103500 and2018YFB1106600)+5 种基金the Science,Technology and Innovation Commission of Shenzhen Municipality(No.JCYJ20180306171121424)the Research Fund of Equipment Development Department(No.61409230402)the Aeronautics Power Foundation(No.6141B09050337)the Innovation Fund of the Zhejiang Kechuang New Materials Research Institute(No.ZKN-18-P04)the Key R&D Program of Shaan Xi Province(No.2018ZDCXL-GY-09-04)the Research Fund of the State Key Laboratory of Solidification Processing(NPU)(No.2019-QZ-02)。
文摘Phase selection and growth characteristics of directionally solidified Al_(2)O_(3)/GdAlO_3(GAP)faceted eutectic ce ramics are investigated over wide ranges of compositions and solidification rates to explore the eutectic coupled zone.Through the obse rvation of the quenched solid-liquid interface,the competitive growth of primary faceted Al_(2)O_(3)phase,prima ry non-faceted GAP phase and Al_(2)O_(3)/GAP eutectic with diffe rent morphologies is detected.Microstructure transitions from wholly eutectic to primary Al_(2)O_(3)(GAP)dendrite plus eutectic and then to wholly eutectic are found in Al_(2)O_(3)-2 O mol%Gd_(2)O_(3)hypoeutectic(Al_(2)O_(3)-26 mol%Gd_(2)O_(3)hypereutectic)ceramics with the increase of solidification rate.The dendrite growth of faceted Al_(2)O_(3)and non-faceted GAP phases are well predicted by KGT model,which have introduced appro p riate dimensionless supersaturationΩto characterize the anisotropic growth of dendrites.Based on the maximum interface temperature criterion,the competitive growth of primary phase and eutectic is analyzed theoretically and the predicted coupled zone of Al_(2)O_(3)/GAP eutectic ceramics is in good agreement with the experimental results.Besides,the influence of microstructure with these different morphologies on the flexural strength of Al_(2)O_(3)/GAP eutectic ceramics is studied.
基金Project(50772090)supported by the National Natural Science Foundation of ChinaProject(04G53048)supported by the Aeronautical Science Foundation of China+4 种基金Project(20040699035)supported by the Specialized Research Fund for the Doctoral Program of Higher Education of ChinaProject(W018101)supported by the Foundation Research Fund of Northwestern Polytechnical University,ChinaProject(2007AMM004)supported by the Opening Project of State Key Laboratory for Advanced Metals and Materials,ChinaProject supported by the Fund of the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University,ChinaProject supported by the Scientific Research Start-up Foundation for Outstanding Persons in Northwestern Polytechnical University,China
文摘Rapid surface resolidification with a high powered CO2-laser was performed in preparing directionally solidified Al2O3/YAG/ZrO2 ternary eutectic ceramic in situ composite.The effects of laser processing parameters on the solidification microstructure characteristics and thermal properties were studied by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),X-ray diffractometry(XRD)and synthetically thermal analysis(STA).Detailed investigations of the influence of laser power and scanning rate on the preparation and microstructural parameters of the ternary eutectic were presented.Moreover, the eutectic phase separation rule at high temperature was discussed.The results indicate that solidification microstructure of the ternary eutectic composite is greatly influenced by the laser processing parameters.The synthetically thermal analysis shows that the eutectic temperature of ternary Al2O3/YAG/ZrO2 composite is 1 738℃,well matching the phase diagram of Al2O3-Y2O3-ZrO2.
基金supported by the National Natural Science Foundation of China (Grant No. 51771152)the National Key Research and Development Program of China (Grant No. 2018YFB1106800)。
文摘Due to the effective precipitation strengthening effect of the β phase, Mg-Gd alloys exhibit excellent room temperature mechanical behaviors. However, when served at high temperatures, the metastable β phase will transform to other phases, resulting in severe performance degradation. In this study, we investigated the effect of precipitation state achieved by different heat treatments on high temperature tensile and creep behaviors of the Mg-15Gd alloy by comparing the properties of the as-cast, solid-solutioned(T4) and peak-aged(T6) alloys. The results showed that the tensile mechanical properties of the T6 alloy were always highest from room temperature to 300 ℃, in spite of an abnormal strength increase with temperature existed in the T4 alloy. For tensile creep properties, the T6 alloy exhibited the lowest steady creep rate below 235 ℃ while the T4 alloy possessed the best properties above 260 ℃. Microstructure characterization revealed that the transition was caused by the stress-promoted precipitation of β phase in the T4 alloy and rapid phase transformation in the T6 alloy at high temperatures. At 260 ℃, the calculated stress exponent n was 3.1 and 2.8 for the T4 and T6 alloys, respectively, suggesting the creep deformation mechanism was dislocation slip, which was further confirmed by the microstructure after creeping. Our findings can provide new insights into the heat treatment process of Mg-Gd alloys served at high temperatures.
基金support from Research Fund of the State Key Laboratory of Solidification Processing (No. 42-QP-009)Fundamental Research Fund of Northwestern Polytechnical University (No. JC200929) the 111 Project (No. B08040)
文摘Solidification behaviour of AA8006 aluminium alloy in suction casting has been investigated by field emission scanning electron microscopy with energy dispersive spectroscopy （EDS）. It is found that there is a secondary solidification process of the remaining liquid in located region of α-Al dendrites, and the cooling rate influences not only the solidification of the primary α-Al dendrite, but also the secondary solidification process of the remaining liquid. With the primary solidification being responsible for the formation of the relatively large α- Al dendrite, a fine and homogeneous microstructure is observed in the secondary solidification. Furthermore, because of the presence of the fine microstructure, the eutectic reaction is confined into small intergranular areas, inducing the formation of the laminar eutectic phase in the primary solidification region and fibrous eutectic phase in the secondary solidification region. EDS analysis shows that the content of Fe is higher in the secondary solidification region, and the enrichment of the solute element further confirms the existence of the secondary solidification.
基金supported by the National Natural Science Foundation of China (Grant No.50771081,50931004)the National Basic Research Program of China (2010CB631202)
文摘A single crystal Ni-based superalloy AM3 was processed at withdraw rates of 3.5, 10, 50, 100, 200, and 500 μm·s-1, respectively.The as-cast microstructures and solidification segregation ratio were characterized with various withdraw rates.The shape and size of carbide microstructures were determined.As expected, the primary and secondary dendrite arm spacings (PDAS and SDAS) decrease with the increase of withdraw rate.The highest volume fraction of eutectic γ/γ' is observed at the 100 μm·s-1 withdraw rate.The volume fraction of eutectic γ/γ' does not appear to be a strong function of the withdraw rate.With increasing withdraw rate, interface morphologies change in the sequence of planar, cellular, and dendrite.There is a general refinement of the microstructure as the withdraw rate increases.EPMA analysis showed that withdraw rate does not have obvious influence on the segregation of elements.
