Structure evolution of an Al-Zn wrought alloy in remelting processing in thestrain induced melt activated (SIMA) serai-solid procedure was observed, and effects of factors, theremelting temperature, the holding time, ...Structure evolution of an Al-Zn wrought alloy in remelting processing in thestrain induced melt activated (SIMA) serai-solid procedure was observed, and effects of factors, theremelting temperature, the holding time, and the compression strain, on structures and grain sizesof the alloy were investigated. The results show that (1) the proper temperature of remelting is inthe range of 610 to 615℃; (2) the grain size in specimen with greater compression strain is smallerthan that with smaller compression strain in condition of the same remelting temperature andholding time, and the grain size in local area with great local equivalent strain is smaller thanthat with small one; (3) liquid occurs in form of cluster in matrix during remelting and itsquantity increases with remelting time increasing; liquid in specimen with great compression strainoccurs earlier than that with small one, and quantity of liquid in the center of specimen withgreater local equivalent strain is greater than that in the two ends of it; (4) distortion energyafter deforming in matrix of the alloy is the significant factor to activate melting of matrix atlocal area with great local equivalent strain.展开更多
Brazing filler metals are widely applied,which serve as an industrial adhesive in the joining of dissimilar structures.With the continuous emergence of new structures and materials,the demand for novel brazing filler ...Brazing filler metals are widely applied,which serve as an industrial adhesive in the joining of dissimilar structures.With the continuous emergence of new structures and materials,the demand for novel brazing filler metals is ever-increasing.It is of great significance to investigate the optimized composition design methods and to establish systematic design guidelines for brazing filler metals.This study elucidated the fundamental rules for the composition design of brazing filler metals from a three-dimensional perspective encompassing the basic properties of applied brazing filler metals,formability and processability,and overall cost.The basic properties of brazing filler metals refer to their mechanical properties,physicochemical properties,electromagnetic properties,corrosion resistance,and the wettability and fluidity during brazing.The formability and processability of brazing filler metals include the processes of smelting and casting,extrusion,rolling,drawing and ring-making,as well as the processes of granulation,powder production,and the molding of amorphous and microcrystalline structures.The cost of brazing filler metals corresponds to the sum of materials value and manufacturing cost.Improving the comprehensive properties of brazing filler metals requires a comprehensive and systematic consideration of design indicators.Highlighting the unique characteristics of brazing filler metals should focus on relevant technical indicators.Binary or ternary eutectic structures can effectively enhance the flow spreading ability of brazing filler metals,and solid solution structures contribute to the formability.By employing the proposed design guidelines,typical Ag based,Cu based,Zn based brazing filler metals,and Sn based solders were designed and successfully applied in major scientific and engineering projects.展开更多
The microstructure evolution and mechanical properties of a ZK60 magnesium alloy produced by the semi-solid thermal transformation （SSTT） route and the recrystallization and partial melting （RAP） route were studie...The microstructure evolution and mechanical properties of a ZK60 magnesium alloy produced by the semi-solid thermal transformation （SSTT） route and the recrystallization and partial melting （RAP） route were studied, respectively. The microstructure evolution during partial remelting was studied at different temperatures for different time. The tensile mechanical properties of thixoformed components by the two routes at room temperature were examined. The results show that coalescence is dominant in the SSTT alloy and Ostwald ripening is dominant in the RAP alloy. Compared with the SSTT route, the RAP route can produce finer semi-solid microstructure under the similar isothermal holding condition. The microstructure of the RAP alloy is much more spheroidized compared with the SSTT alloy. Thixoforming for the ZK60 magnesium alloy produced by the SSTT and RAP route results in successful filling of the die, and the thixoforming process improves the mechanical properties of ZK60 magnesium alloy. The RAP alloy shows significantly advantageous mechanical properties over that of the SSTT alloy.展开更多
Polymeric perylene diimide(PDI)has been evidenced as a good candidate for photocatalytic water oxidation,yet the origin of the photocatalytic oxygen evolution activity remains unclear and needs further exploration.Her...Polymeric perylene diimide(PDI)has been evidenced as a good candidate for photocatalytic water oxidation,yet the origin of the photocatalytic oxygen evolution activity remains unclear and needs further exploration.Herein,with crystal and atomic structures of the self-assembled PDI revealed from the X-ray diffraction pattern,the electronic structure is theoretically illustrated by the first-principles density functional theory calculations,suggesting the suitable band structure and the direct electronic transition for efficient photocatalytic oxygen evolution over PDI.It is confirmed that the carbonyl O atoms on the conjugation structure serve as the active sites for oxygen evolution reaction by the crystal orbital Hamiltonian group analysis.The calculations of reaction free energy changes indicate that the oxygen evolution reaction should follow the reaction pathway of H_(2)O→^(*)OH→^(*)O→^(*)OOH→^(*)O_(2)with an overpotential of 0.81 V.Through an in-depth theoretical computational analysis in the atomic and electronic structures,the origin of photocatalytic oxygen evolution activity for PDI is well illustrated,which would help the rational design and modification of polymeric photocatalysts for efficient oxygen evolution.展开更多
Addressing the kinetic limitations of oxygen evolution reaction(OER)is paramount for advancing rechargeable Zn-air batteries,thus it is extremely urgent to drive the development of effective and affordable electrocata...Addressing the kinetic limitations of oxygen evolution reaction(OER)is paramount for advancing rechargeable Zn-air batteries,thus it is extremely urgent to drive the development of effective and affordable electrocatalysts.This work constructs the interfacial structure of cobalt-iron alloys@phosphates(denoted as CoFe/CoFePO)as OER catalyst through a two-step approach using water-bath and hydrothermal methods,which demonstrated significant OER activity in alkaline media,requiring a low overpotential of 271 mV to achieve 10 mA cm^(−2) and exhibiting a competitive Tafel slope of 65 mV dec^(-1),alongside sustained operational stability.The enhanced performance can be attributed to the improved electrical conductivity due to the participation of CoFe alloys and the increased number of active sites through partial phosphorylation,which synergistically enhances charge transfer processes and accelerates OER kinetics.Moreover,dynamic structural evolution during OER process was thoroughly probed,and the results show that alloys@phosphates gradually evolve into phosphate radicalmodified CoFe hydroxyoxides that act as the actual active phase.Highlighting its practical applicability,the integration of prepared catalyst into zinc-air batteries leads to markedly improved performance,thereby offering promising new strategic directions for the development of next-generation OER electrocatalysts.展开更多
Pyrochlore oxide(Y_(2)Ru_(2)O_(7))has been identified as a promising catalyst for the oxygen evolution reaction(OER)in advanced green energy strategies.However,its electrochemical inertness necessitates the exploratio...Pyrochlore oxide(Y_(2)Ru_(2)O_(7))has been identified as a promising catalyst for the oxygen evolution reaction(OER)in advanced green energy strategies.However,its electrochemical inertness necessitates the exploration of an effective strategy to facilitate electronic modulation.This study proposes a surface modification approach involving the integration of defective NiFe(D-NiFe)nanoparticles onto a Y_(2)Ru_(2)O_(7)(YRO)support(YRO@D-NiFeP/Ru)using a Prussian blue analog(PBA).Numerous cyanide(CN)vacancies are generated through the oxidation treatment of the NiFe PBA grown on the YRO support,yielding a defective PBA precursor(YRO@D-PBA).Subsequent annealing facilitates the transformation to the D-NiFe nanoparticles on the YRO support(YRO@D-NiFeP/Ru),which augments the exposure of Ni3+active sites beneficial for the OER.Moreover,the reduction of Ru cations from YRO results in the exsolution of Ru nanoparticles,which promotes synergistic charge transfer from the nanoparticles to the interior of Y_(2)Ru_(2)O_(7).Consequently,YRO@D-NiFeP/Ru exhibits a remarkable voltage of 1.49 V at 10 mA·cm^(−2) and the lowest Tafel slope of 42.4 mV·dec^(−1).In addition,a Zn–air battery constructed with YRO@D-NiFeP/Ru exhibits an outstanding power density of 136.2 mW·cm^(−2) and high charge–discharge stability,confirming the applicability of YRO@D-NiFeP/Ru in metal-air batteries.展开更多
Deep-buried tunnels traversing complex hydrogeological zones with clay-sand-filled structures are highly susceptible to water inrush hazards.High ground temperature,high in-situ stress,and highwater pressure render th...Deep-buried tunnels traversing complex hydrogeological zones with clay-sand-filled structures are highly susceptible to water inrush hazards.High ground temperature,high in-situ stress,and highwater pressure render these events a complex thermohydro-mechanical coupling problem.However,current research on water inrush often insufficiently investigates the multi-field coupled instability mechanisms within highly permeable filling media and frequently neglects the influence of temperature.This study aims to investigate the evolutionary mechanism of seepage instability in filling structures that trigger water inrush hazards under the complex conditions of deep-buried tunnels.Laboratory tests were conducted using a large-scale triaxial thermo-hydro-mechanical system,and a DEM-CFD coupled model was established to numerically simulate the seepage process.The influences of temperature,particle size distribution,and confining pressure were analyzed on the seepage characteristics of the filling media.By examining the variations in water inflow rate,discharged clay-sand particle mass,porosity and permeability,we analyzed the entire process of seepage behavior and instability evolution under the thermohydro-mechanical coupling effect.The results show that:(1)Temperature significantly affects water inflow,discharged particle mass,porosity,and permeability.Higher temperatures remarkably increase porosity and permeability,with the maximum permeability coefficient of filling media at 90℃being 1.6 times that at 45℃.(2)The Talbol power index exhibits a positive correlation with water inflow rate and discharged particle mass,while confining pressure is negatively correlated with water inflow rate.(3)For filling materials dominated by clay-sand particles or with favorable gradation,the seepage instability process exhibits distinct phase characteristics,with different stages reflected in changes in water inflow,porosity,and permeability.The experimental results are consistent with the numerical simulation results.(4)In high ground temperature environments,temperature enhances convective heat transfer and energy exchange between water and filling media,thereby accelerating the process of water inrush caused by seepage instability.The findings provide scientific support for risk assessment,early warning,and prevention of water inrush hazards in deep-buried tunnels crossing clay-sand-filled structures.展开更多
Hydrogen production coupled with small molecule oxidation derived by renewable energy power has been widely studied as an effective method to reduce energy consumption and prepare added value production.Here,the coppe...Hydrogen production coupled with small molecule oxidation derived by renewable energy power has been widely studied as an effective method to reduce energy consumption and prepare added value production.Here,the copper-cobalt phosphide with a multilevel structure has been designed based on the hard and soft acids and bases theory.The nanocone composed of lamellas presented a sharp tip,which a positive effect on the mass transfer enhanced by a local electric field,and the nanolamellas contain CoP/Cu_(3)P interface provide the highly selective active site for the gluconic acid(GNA)synthesis and hydrogen evolution.The catalyst can drive hydrogen evolution at 5 A·cm^(-2)up to 437 h without active decay,and the electrocatalytic glucose oxidation at anode presents high efficiency due to Cu(I)introduction and the synergetic effect between interfaces.Density functional theory(DFT)calculation shows that water splitting more readily occurs at the CoP,which provides adsorbed H and-OH for hydrogen evolution and glucose oxidation,respectively,and glucose adsorption more readily occurs at the Cu_(3)P,which presents lower conversion energy for high value-added GNA.Efficient hydrogen evolution and glucose conversion indicate its high intrinsic activity and synergetic effect.This work provides a special interface construction strategy for the catalytic conversion of hydrogen and small molecules.展开更多
The development of cost-effective and highly stable electrocatalysts for oxygen evolution reactions holds paramount importance in practical hydrogen production.Herein,we present a novel self-supported electrode compri...The development of cost-effective and highly stable electrocatalysts for oxygen evolution reactions holds paramount importance in practical hydrogen production.Herein,we present a novel self-supported electrode comprising Ce-doped Ni-Fe-Se nanosheets grown on carbon cloth(Ni-Fe-Ce-Se/CC).This electrode was synthesized through a selenylation process,utilizing Ni-Fe-Ce-layered double hydroxide/carbon cloth(Ni-Fe-Ce LDH/CC)as the precursor.Notably,Ni-Fe-Ce-Se/CC electrode demonstrates remarkable performance,requiring a low overpotential of 300 mV to attain a current density of 100 mA·cm^(-2)under harsh alkaline conditions.Furthermore,the electrode exhibits exceptional stability during continuous operation for 100 h.Insight into the underlying mechanisms was gained through a combination of experimental results and density functional theory calculations.Our findings reveal that Ce doping induces crystal structure deformation in Ni-Fe-Se and enhances electron enrichment around Ni atoms.This structural modification optimizes the adsorption energy of oxygen-based intermediates on the Ni-Fe-Se surface.This work offers a valuable strategy for regulating the electron transfer and adsorption capabilities of transition metal selenide electrocatalysts through RE atoms doping,opening new avenues for enhanced electrocatalytic performance.展开更多
The toughness of thermoplastic polymers such as polypropylene(PP)can be improved by adding elastomers-based toughening agents,and the phase morphology of these toughening agents is very important for the strength and ...The toughness of thermoplastic polymers such as polypropylene(PP)can be improved by adding elastomers-based toughening agents,and the phase morphology of these toughening agents is very important for the strength and toughness of PP.The low-temperature toughness of PP was improved by inserting high-density polyethylene(HDPE)between PP and polystyrene-b-ethylene-co-propyleneb-polystyrene(SEPS)to form an unusual SEPS@HDPE core–shell structure,with SEPS as the core and HDPE as the shell.Based on the microtopography and rheological behavior characterization,HDPE in PP/SEPS/HDPE composites was found to serve as an emulsifier,decrease the size of SEPS particles,and promote the homogeneous dispersion of dispersed phase particles in the matrix.An increase in the HDPE content shifted the toughening mechanism of PP composites from cavitation to matrix shear yielding.The reduction in the distance between the dispersed core–shell structure particles promoted shear yielding in the PP composites,leading to increased toughness.The creation of an intermediate HDPE layer with a moderate modulus was crucial for dispersing stress concentrations and significantly improving toughness without compromising the tensile strength.These findings will facilitate the fabrication of high-toughness PP products at low temperatures.展开更多
AZ31 Mg alloy plates with bimodal grain structures were fabricated via conventional extrusion under varying temperatures and speeds to investigate the mechanisms governing dynamic recrystallization(DRX)and texture evo...AZ31 Mg alloy plates with bimodal grain structures were fabricated via conventional extrusion under varying temperatures and speeds to investigate the mechanisms governing dynamic recrystallization(DRX)and texture evolution.Although all samples exhibited similar DRXed grain sizes(5.0–6.5μm)and fractions(76%–80%),they developed distinct c-axis orientations and mechanical properties.The P1 sample(350℃,0.1 mm/min)exhibited the lowest yield strength(∼192 MPa)but the highest elongation(∼18.2%),whereas the P3 sample(400℃,0.6 mm/min)showed the highest yield strength(∼241 MPa)and the lowest elongation(∼14.2%).The P2 sample(400℃,0.1 mm/min)demonstrated intermediate behavior(∼226 MPa,∼17.7%).These variations were primarily attributed to differences in c-axis orientations,particularly their alignment with respect to the normal direction(ND)and their slight deviation from the extrusion direction(ED).Microstructural analysis revealed that distinct DRX mechanisms were activated under different extrusion conditions.P1 predominantly exhibited twinning-induced dynamic recrystallization(TDRX)and continuous dynamic recrystallization(CDRX),whereas P3 primarily showed CDRX and discontinuous dynamic recrystallization(DDRX).These DRX mechanisms,in combination with the activated slip systems governed by the evolving local stress state,collectively contributed to orientation rotation and texture development.During the early stage of extrusion,tensile strain along the ED promoted basalslip,rotating the c-axes toward the ND.As deformation progressed,compressive strain along the ND became dominant.In P1,basalslip remained active,aligning the c-axes along the ND and forming a smaller angle with the ED.In contrast,P3 exhibited predominant pyramidal<c+a>slip,resulting in a pronounced deviation of the c-axes from the ND and a slightly larger angle relative to the ED.The P2 sample exhibited a transitional texture state between those of P1 and P3.展开更多
The development of atomically dispersed platinum-based catalysts with high performance and welldefined active site structures is crucial for the commercialization of water electrolysis for hydrogen production.Herein,w...The development of atomically dispersed platinum-based catalysts with high performance and welldefined active site structures is crucial for the commercialization of water electrolysis for hydrogen production.Herein,we propose a coordination dual-shell synergistic regulation mechanism of coal pitchderived carbon-supported single atom Pt-N_(x)O_(y)-S_(1)catalytic sites by a self-assembly-pyrolysis strategy for promoting hydrogen evolution reaction(HER).The Pt-N_(3)O1-S_(1)sites exhibited the highest HER performance,with an overpotential of 92 mV at a current density of 400 mA cm^(-2).At 50 mV,the turnover frequency was 34.04 s^(-1)and the mass activity was 22.83 A mg_(Pt)^(-l),which is 63.4 times that of the 20%Pt/C catalyst.Theoretical calculations revealed that the coordination dual-shell impacts the electronic structure of the Pt atoms and the adsorption strength towards reactants synergistically.The S atoms in the second coordination shell weakened the strength of Pt-N first shell,resulting the more surface valence electrons around Pt atoms,exhibiting the most suitable adsorption free energy and enhancing the adsorption of H^(+)on Pt-N_(3)O_(1)-S_(1)sites,thus enhancing the electrocatalytic HER process by promoting Volmer step.This work reveals that coordination dual-shell synergistic regulation is an effective strategy for enhancing the electrocatalytic reaction process.展开更多
A series of CoS_(2-x)Se_(x)(x=0.05,0.1,0.2,0.3,and 2)composite catalysts were synthesized on carbon fiber paper via the hydrothermal method with Se doping.By precisely controlling the reaction temperature and Se dopin...A series of CoS_(2-x)Se_(x)(x=0.05,0.1,0.2,0.3,and 2)composite catalysts were synthesized on carbon fiber paper via the hydrothermal method with Se doping.By precisely controlling the reaction temperature and Se doping level,a hollow spherical catalyst structure composed of CoSSe was successfully synthesized,which exhibited exceptional activity for hydrogen evolution in acidic solutions.The influences of Se doping on the microstructure and catalytic mechanism of hydrogen evolution reaction(HER)of these composites were systematically investigated.The experimental results reveal that the hollow spherical sample displays an overpotential value of 143 mV along with a Tafel slope value of 69.8 mV·dec^(-1)at a current density of 10 mA·cm^(-2)in an acid aqueous solution.Furthermore,it demonstrates remarkable cycling stability after undergoing 3000 cycles.The comprehensive analysis indicates that Se doping optimizes the electronic structure and enhances conductivity,meanwhile the unique hollow spherical architecture increases active sites for HER and significantly improves overall electrocatalytic performance.展开更多
Atomically precise palladium(Pd)clusters are emerging as versatile nanomaterials with applications in catalysis and biomedicine.This study explores the synthesis,structure evolution,and catalytic properties of Pd clus...Atomically precise palladium(Pd)clusters are emerging as versatile nanomaterials with applications in catalysis and biomedicine.This study explores the synthesis,structure evolution,and catalytic properties of Pd clusters stabilized by cyclohexanethiol(HSC_(6)H_(11))ligands.Using electrospray ionization mass spectrometry(ESI-MS)and single-crystal X-ray diffraction(SXRD),structures of the Pd clusters ranging from Pd4(SC_(6)H_(11))8 to Pd18(SC_(6)H_(11))36 were determined.This analysis revealed a structure evolution from polygonal to elliptical geometries of the PdnS2n frameworks as the cluster size increased.UV-Vis-NIR spectroscopy,combined with quantum chemical calculations,elucidated changes in the electronic structure of the clusters.Catalytic studies on the Sonogashira cross-coupling reactions demonstrated a size-dependent decline in activity attributed to variations in structural arrangements and electronic properties.Mechanistic insights proposed a distinctive Pd(Ⅱ)-Pd(Ⅳ)catalytic cycle.This research underscores how ligands and cluster size influence the structures and properties of Pd clusters,offering valuable insights for the future design and application of Pd clusters in advanced catalysis and beyond.展开更多
Li/MnO_(2) primary batteries are widely used in industry for their high specific capacity and safety.However,a deep comprehension of the Li^(+)insertion mechanism and the high self-discharge rate of the batteries is s...Li/MnO_(2) primary batteries are widely used in industry for their high specific capacity and safety.However,a deep comprehension of the Li^(+)insertion mechanism and the high self-discharge rate of the batteries is still needed.Here,the storage mechanism of Li^(+)in the tunnel structure of MnO_(2) as well as the dissolution and migration of Mn-ions were investigated based on multi-scale approaches.The Li/Mn ratio(at%)is determined at about 0.82 when the discharge voltage decreases to 2 V.The limited Li-ions transport rate in the bulk MnO_(2) restrains the reduction reaction,resulting in a low practical specific capacity.Moreover,utilizing spherical aberration-corrected transmission electron microscopy(TEM)coupled with electron energy loss spectroscopy(EELS),the presence of a mixed valence state layer of Mn^(2+)/Mn^(3+)/Mn^(4+)on the surface of the original 20 nm MnO_(2) particles was identified,which could contribute to the initial dissolution of Mn-ions.The battery separator exhibited channels for Mn-ions migration and diffusion and aggregated Mn particles.We put forward the discharge and degradation route in the ways of Mn-ions trajectories,and our findings provide a deep understanding of the high self-discharge rates and the capacity decay of Li-Mn primary batteries.展开更多
Semi-solid metal processing is being developed in die casting applications to give several cost benefits. To efficiently apply this emerging technology, it is important to understand the evolution of microstructure in...Semi-solid metal processing is being developed in die casting applications to give several cost benefits. To efficiently apply this emerging technology, it is important to understand the evolution of microstructure in semi-solid slurries for the control of the theological behavior in semi-solid state. An experimental apparatus was developed which can capture the grain structure at different times at early stages to understand how the semi-solid structure evolves. In this technique, semi-solid slurry was produced by injecting fine gas bubbles into the melt through a graphite diffuser during solidification. Then, a copper quenching mold was used to draw some semi-solid slurry into a thin channel. The semi-solid slurry was then rapidly frozen in the channel giving the microstructure of the slurry at the desired time. Samples of semi-solid 356 aluminum alloy were taken at different gas injection times of 1, 5, 10, 15, 20, 30, 35, 40, and 45 s. Analysis of the microstructure suggests that the fragmentation by remelting mechanism should be responsible for the formation of globular structure in this rheocasting process.展开更多
Cylindrical samples of Ni-based GH4037 alloy were compressed at solid temperatures(1200,1250 and 1300℃) and semi-solid temperatures(1340,1350,1360,1370 and 1380℃) with different strain rates of 0.01,0.1 and 1 s-1.Hi...Cylindrical samples of Ni-based GH4037 alloy were compressed at solid temperatures(1200,1250 and 1300℃) and semi-solid temperatures(1340,1350,1360,1370 and 1380℃) with different strain rates of 0.01,0.1 and 1 s-1.High temperature deformation behavior and microstructure evolution of GH4037 alloy were investigated.The results indicated that flow stress decreased rapidly at semi-solid temperatures compared to that at solid temperatures.Besides,the flow stress continued to increase after reaching the initial peak stress at semi-solid temperatures when the strain rate was 1 s-1.With increasing the deformation temperature,the size of initial solid grains and recrystallized grains increased.At semi-solid temperatures,the grains were equiaxed,and liquid phase existed at the grain boundaries and inside the grains.Discontinuous dynamic recrystallization(DDRX) characterized by grain boundary bulging was the main nucleation mechanism for GH4037 alloy.展开更多
The self-developed taper barrel rheomoulding (TBR) machine for light alloy semi-solid slurry preparation was introduced.The semi-solid slurry was obtained from the intense shearing turbulence of the alloy melt in the ...The self-developed taper barrel rheomoulding (TBR) machine for light alloy semi-solid slurry preparation was introduced.The semi-solid slurry was obtained from the intense shearing turbulence of the alloy melt in the cause of solidification, which was further caused by the relative rotation of the internal and external taper barrel whose surface contained wale and groove.The heat transmission model of TBR process, the flow rules and the shearing model of the alloy melt were deduced.Taking A365 as experimental material, the microstructure evolution rules under different slurry preparation processes were analyzed.The results show that decreasing the pouring temperature of A365 alloy melt properly or increasing the shearing rate helps to obtain ideal semi-solid microstructure with the primary particle size of about 70 μm and the shape factor of above 0.8.展开更多
The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of...The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of ZC61 magnesium alloy were investigated by metal mold casting and semi-solid isothermal heat treatment. The results show that the addition of Cr can refine the α-Mg phase without generating a new phase, noticeably change the eutectic phase, and decrease the average size of solid particles at the same isothermal heat treatment conditions. Non-dendritic microstructures of all alloys are constituted of α_1-Mg phases, α_2-Mg phases and eutectic phases after water quenching. With isothermal temperature increased or holding time prolonged, the eutectic microstructure(α-Mg+MgZn_2+CuMgZn) at the grain boundaries in as-cast alloy is melted preferentially and then turned into semi-solid non-dendritic microstructure by processes of initial coarsening, microstructure separation, spheroidizing and final coarsening. Especially when the ZC61-0.1 Cr alloy was treated at 585 ℃ for 30 min, the ideal non-dendritic microstructure can be obtained, and the corresponding solid particle size and shape factor were 37.5 μm and 1.33, respectively. The coarsening process of solid α-Mg phase at higher temperature or longer time, which is affected by both combining growth and Ostwald ripening mechanism, is refrained when Cr is added to the ZC61 alloy.展开更多
A new Mg-14Al-0.5Mn alloy that exhibits a wide solidification range and sufficient fluidity for semi-solid forming was designed. And the rnicrostructure evolution of semi-solid Mg-14Al-0.5Mn alloy during isothermal he...A new Mg-14Al-0.5Mn alloy that exhibits a wide solidification range and sufficient fluidity for semi-solid forming was designed. And the rnicrostructure evolution of semi-solid Mg-14Al-0.5Mn alloy during isothermal heat treatment was investigated. The mechanism of the microstructure evolution and the processing conditions for isothermal heat treatment were also discussed. The results show that the microstructures of cast alloys consist of α-Mg,β-Mg17Al12 and a small amount of Al-Mn compounds. After holding at 520 ℃ for 3 min, the phases of β-Mg17Al12 and eutectic mixtures in the Mg-14Al-0.5Mn alloy melt and the microstructures of α-Mg change from developed dendrites to irregular solid particles. With increasing the isothermal time, the amount of liquid increases, and the solid particles grow large and become spherical. When the holding time lasts for 20 min or even longer, the solid and liquid phases achieve a state of dynamic equilibrium.展开更多
文摘Structure evolution of an Al-Zn wrought alloy in remelting processing in thestrain induced melt activated (SIMA) serai-solid procedure was observed, and effects of factors, theremelting temperature, the holding time, and the compression strain, on structures and grain sizesof the alloy were investigated. The results show that (1) the proper temperature of remelting is inthe range of 610 to 615℃; (2) the grain size in specimen with greater compression strain is smallerthan that with smaller compression strain in condition of the same remelting temperature andholding time, and the grain size in local area with great local equivalent strain is smaller thanthat with small one; (3) liquid occurs in form of cluster in matrix during remelting and itsquantity increases with remelting time increasing; liquid in specimen with great compression strainoccurs earlier than that with small one, and quantity of liquid in the center of specimen withgreater local equivalent strain is greater than that in the two ends of it; (4) distortion energyafter deforming in matrix of the alloy is the significant factor to activate melting of matrix atlocal area with great local equivalent strain.
基金National Natural Science Foundation of China(U22A20191)。
文摘Brazing filler metals are widely applied,which serve as an industrial adhesive in the joining of dissimilar structures.With the continuous emergence of new structures and materials,the demand for novel brazing filler metals is ever-increasing.It is of great significance to investigate the optimized composition design methods and to establish systematic design guidelines for brazing filler metals.This study elucidated the fundamental rules for the composition design of brazing filler metals from a three-dimensional perspective encompassing the basic properties of applied brazing filler metals,formability and processability,and overall cost.The basic properties of brazing filler metals refer to their mechanical properties,physicochemical properties,electromagnetic properties,corrosion resistance,and the wettability and fluidity during brazing.The formability and processability of brazing filler metals include the processes of smelting and casting,extrusion,rolling,drawing and ring-making,as well as the processes of granulation,powder production,and the molding of amorphous and microcrystalline structures.The cost of brazing filler metals corresponds to the sum of materials value and manufacturing cost.Improving the comprehensive properties of brazing filler metals requires a comprehensive and systematic consideration of design indicators.Highlighting the unique characteristics of brazing filler metals should focus on relevant technical indicators.Binary or ternary eutectic structures can effectively enhance the flow spreading ability of brazing filler metals,and solid solution structures contribute to the formability.By employing the proposed design guidelines,typical Ag based,Cu based,Zn based brazing filler metals,and Sn based solders were designed and successfully applied in major scientific and engineering projects.
文摘The microstructure evolution and mechanical properties of a ZK60 magnesium alloy produced by the semi-solid thermal transformation （SSTT） route and the recrystallization and partial melting （RAP） route were studied, respectively. The microstructure evolution during partial remelting was studied at different temperatures for different time. The tensile mechanical properties of thixoformed components by the two routes at room temperature were examined. The results show that coalescence is dominant in the SSTT alloy and Ostwald ripening is dominant in the RAP alloy. Compared with the SSTT route, the RAP route can produce finer semi-solid microstructure under the similar isothermal holding condition. The microstructure of the RAP alloy is much more spheroidized compared with the SSTT alloy. Thixoforming for the ZK60 magnesium alloy produced by the SSTT and RAP route results in successful filling of the die, and the thixoforming process improves the mechanical properties of ZK60 magnesium alloy. The RAP alloy shows significantly advantageous mechanical properties over that of the SSTT alloy.
基金supported by National Natural Science Foundation of China(No.523B2070,No.52225606).
文摘Polymeric perylene diimide(PDI)has been evidenced as a good candidate for photocatalytic water oxidation,yet the origin of the photocatalytic oxygen evolution activity remains unclear and needs further exploration.Herein,with crystal and atomic structures of the self-assembled PDI revealed from the X-ray diffraction pattern,the electronic structure is theoretically illustrated by the first-principles density functional theory calculations,suggesting the suitable band structure and the direct electronic transition for efficient photocatalytic oxygen evolution over PDI.It is confirmed that the carbonyl O atoms on the conjugation structure serve as the active sites for oxygen evolution reaction by the crystal orbital Hamiltonian group analysis.The calculations of reaction free energy changes indicate that the oxygen evolution reaction should follow the reaction pathway of H_(2)O→^(*)OH→^(*)O→^(*)OOH→^(*)O_(2)with an overpotential of 0.81 V.Through an in-depth theoretical computational analysis in the atomic and electronic structures,the origin of photocatalytic oxygen evolution activity for PDI is well illustrated,which would help the rational design and modification of polymeric photocatalysts for efficient oxygen evolution.
基金supported by the National Natural Science Foundation of China(No.52002122).
文摘Addressing the kinetic limitations of oxygen evolution reaction(OER)is paramount for advancing rechargeable Zn-air batteries,thus it is extremely urgent to drive the development of effective and affordable electrocatalysts.This work constructs the interfacial structure of cobalt-iron alloys@phosphates(denoted as CoFe/CoFePO)as OER catalyst through a two-step approach using water-bath and hydrothermal methods,which demonstrated significant OER activity in alkaline media,requiring a low overpotential of 271 mV to achieve 10 mA cm^(−2) and exhibiting a competitive Tafel slope of 65 mV dec^(-1),alongside sustained operational stability.The enhanced performance can be attributed to the improved electrical conductivity due to the participation of CoFe alloys and the increased number of active sites through partial phosphorylation,which synergistically enhances charge transfer processes and accelerates OER kinetics.Moreover,dynamic structural evolution during OER process was thoroughly probed,and the results show that alloys@phosphates gradually evolve into phosphate radicalmodified CoFe hydroxyoxides that act as the actual active phase.Highlighting its practical applicability,the integration of prepared catalyst into zinc-air batteries leads to markedly improved performance,thereby offering promising new strategic directions for the development of next-generation OER electrocatalysts.
基金supported by Korea Institute of Energy Technology Evaluation and Planning(KETEP)grant funded by the Korea government(MOTIE)(No.RS-2024-00398346,ESS BigData-Based O&M and Asset Management Technical Manpower Training)the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(No.RS-2024-00350658).
文摘Pyrochlore oxide(Y_(2)Ru_(2)O_(7))has been identified as a promising catalyst for the oxygen evolution reaction(OER)in advanced green energy strategies.However,its electrochemical inertness necessitates the exploration of an effective strategy to facilitate electronic modulation.This study proposes a surface modification approach involving the integration of defective NiFe(D-NiFe)nanoparticles onto a Y_(2)Ru_(2)O_(7)(YRO)support(YRO@D-NiFeP/Ru)using a Prussian blue analog(PBA).Numerous cyanide(CN)vacancies are generated through the oxidation treatment of the NiFe PBA grown on the YRO support,yielding a defective PBA precursor(YRO@D-PBA).Subsequent annealing facilitates the transformation to the D-NiFe nanoparticles on the YRO support(YRO@D-NiFeP/Ru),which augments the exposure of Ni3+active sites beneficial for the OER.Moreover,the reduction of Ru cations from YRO results in the exsolution of Ru nanoparticles,which promotes synergistic charge transfer from the nanoparticles to the interior of Y_(2)Ru_(2)O_(7).Consequently,YRO@D-NiFeP/Ru exhibits a remarkable voltage of 1.49 V at 10 mA·cm^(−2) and the lowest Tafel slope of 42.4 mV·dec^(−1).In addition,a Zn–air battery constructed with YRO@D-NiFeP/Ru exhibits an outstanding power density of 136.2 mW·cm^(−2) and high charge–discharge stability,confirming the applicability of YRO@D-NiFeP/Ru in metal-air batteries.
基金funded by National Natural Science Foundation of China(Grant No.52278404)Taishan Young Scholar Program of Shandong Province(Grant No.tsqn202103002),which collectively funded this project。
文摘Deep-buried tunnels traversing complex hydrogeological zones with clay-sand-filled structures are highly susceptible to water inrush hazards.High ground temperature,high in-situ stress,and highwater pressure render these events a complex thermohydro-mechanical coupling problem.However,current research on water inrush often insufficiently investigates the multi-field coupled instability mechanisms within highly permeable filling media and frequently neglects the influence of temperature.This study aims to investigate the evolutionary mechanism of seepage instability in filling structures that trigger water inrush hazards under the complex conditions of deep-buried tunnels.Laboratory tests were conducted using a large-scale triaxial thermo-hydro-mechanical system,and a DEM-CFD coupled model was established to numerically simulate the seepage process.The influences of temperature,particle size distribution,and confining pressure were analyzed on the seepage characteristics of the filling media.By examining the variations in water inflow rate,discharged clay-sand particle mass,porosity and permeability,we analyzed the entire process of seepage behavior and instability evolution under the thermohydro-mechanical coupling effect.The results show that:(1)Temperature significantly affects water inflow,discharged particle mass,porosity,and permeability.Higher temperatures remarkably increase porosity and permeability,with the maximum permeability coefficient of filling media at 90℃being 1.6 times that at 45℃.(2)The Talbol power index exhibits a positive correlation with water inflow rate and discharged particle mass,while confining pressure is negatively correlated with water inflow rate.(3)For filling materials dominated by clay-sand particles or with favorable gradation,the seepage instability process exhibits distinct phase characteristics,with different stages reflected in changes in water inflow,porosity,and permeability.The experimental results are consistent with the numerical simulation results.(4)In high ground temperature environments,temperature enhances convective heat transfer and energy exchange between water and filling media,thereby accelerating the process of water inrush caused by seepage instability.The findings provide scientific support for risk assessment,early warning,and prevention of water inrush hazards in deep-buried tunnels crossing clay-sand-filled structures.
基金supported by the National Nature Science Foundation of China(No.22269021)Tianshan Talent Project of Xinjiang Uygur Autonomous Region(No.2023TSYCQNTJ0039)the Open project of Key Laboratory in Xinjiang Uygur Autonomous Region of China(No.2023D04027).
文摘Hydrogen production coupled with small molecule oxidation derived by renewable energy power has been widely studied as an effective method to reduce energy consumption and prepare added value production.Here,the copper-cobalt phosphide with a multilevel structure has been designed based on the hard and soft acids and bases theory.The nanocone composed of lamellas presented a sharp tip,which a positive effect on the mass transfer enhanced by a local electric field,and the nanolamellas contain CoP/Cu_(3)P interface provide the highly selective active site for the gluconic acid(GNA)synthesis and hydrogen evolution.The catalyst can drive hydrogen evolution at 5 A·cm^(-2)up to 437 h without active decay,and the electrocatalytic glucose oxidation at anode presents high efficiency due to Cu(I)introduction and the synergetic effect between interfaces.Density functional theory(DFT)calculation shows that water splitting more readily occurs at the CoP,which provides adsorbed H and-OH for hydrogen evolution and glucose oxidation,respectively,and glucose adsorption more readily occurs at the Cu_(3)P,which presents lower conversion energy for high value-added GNA.Efficient hydrogen evolution and glucose conversion indicate its high intrinsic activity and synergetic effect.This work provides a special interface construction strategy for the catalytic conversion of hydrogen and small molecules.
基金supported by the National Key Technology R&D Program of China(Nos.2021YFB3500801,2022YFB3504302 and 2022YFC3901503)the Natural Science Foundation and Overseas Talent Projects of Jiangxi Province(Nos.0232BAB214025 and 20232BCJ25044)the Double Thousand Plan of Jiangxi Province(No.jxsq2023201002).
文摘The development of cost-effective and highly stable electrocatalysts for oxygen evolution reactions holds paramount importance in practical hydrogen production.Herein,we present a novel self-supported electrode comprising Ce-doped Ni-Fe-Se nanosheets grown on carbon cloth(Ni-Fe-Ce-Se/CC).This electrode was synthesized through a selenylation process,utilizing Ni-Fe-Ce-layered double hydroxide/carbon cloth(Ni-Fe-Ce LDH/CC)as the precursor.Notably,Ni-Fe-Ce-Se/CC electrode demonstrates remarkable performance,requiring a low overpotential of 300 mV to attain a current density of 100 mA·cm^(-2)under harsh alkaline conditions.Furthermore,the electrode exhibits exceptional stability during continuous operation for 100 h.Insight into the underlying mechanisms was gained through a combination of experimental results and density functional theory calculations.Our findings reveal that Ce doping induces crystal structure deformation in Ni-Fe-Se and enhances electron enrichment around Ni atoms.This structural modification optimizes the adsorption energy of oxygen-based intermediates on the Ni-Fe-Se surface.This work offers a valuable strategy for regulating the electron transfer and adsorption capabilities of transition metal selenide electrocatalysts through RE atoms doping,opening new avenues for enhanced electrocatalytic performance.
基金supported by the Taiyuan Major Science and Technology Project Fund in 2021,Fund for Shanxi“1331 Project,”Key Research and Development Program of Shanxi Province(202102040201011)the Zhanjiang Marine Equipment and Marine Biological Industry Unveiled the Talent Team Project(2021E05034).
文摘The toughness of thermoplastic polymers such as polypropylene(PP)can be improved by adding elastomers-based toughening agents,and the phase morphology of these toughening agents is very important for the strength and toughness of PP.The low-temperature toughness of PP was improved by inserting high-density polyethylene(HDPE)between PP and polystyrene-b-ethylene-co-propyleneb-polystyrene(SEPS)to form an unusual SEPS@HDPE core–shell structure,with SEPS as the core and HDPE as the shell.Based on the microtopography and rheological behavior characterization,HDPE in PP/SEPS/HDPE composites was found to serve as an emulsifier,decrease the size of SEPS particles,and promote the homogeneous dispersion of dispersed phase particles in the matrix.An increase in the HDPE content shifted the toughening mechanism of PP composites from cavitation to matrix shear yielding.The reduction in the distance between the dispersed core–shell structure particles promoted shear yielding in the PP composites,leading to increased toughness.The creation of an intermediate HDPE layer with a moderate modulus was crucial for dispersing stress concentrations and significantly improving toughness without compromising the tensile strength.These findings will facilitate the fabrication of high-toughness PP products at low temperatures.
基金supported by National Key Research&Development Program of China(Grant no.2022YFE0110600)National Natural Science Foundation(Grant no.52220105003)+3 种基金the State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology(Grant no.XNDCQQ2910201124)the National Natural Science Foundation for Young Scientists of China(Grant nos.51801042 and 51704088)Natural Science Foundation of Heilongjiang Province-Outstanding Youth Fund(Grant no.YQ2020E006)JSPS KAKENHI(Grant no.JP21H01669).
文摘AZ31 Mg alloy plates with bimodal grain structures were fabricated via conventional extrusion under varying temperatures and speeds to investigate the mechanisms governing dynamic recrystallization(DRX)and texture evolution.Although all samples exhibited similar DRXed grain sizes(5.0–6.5μm)and fractions(76%–80%),they developed distinct c-axis orientations and mechanical properties.The P1 sample(350℃,0.1 mm/min)exhibited the lowest yield strength(∼192 MPa)but the highest elongation(∼18.2%),whereas the P3 sample(400℃,0.6 mm/min)showed the highest yield strength(∼241 MPa)and the lowest elongation(∼14.2%).The P2 sample(400℃,0.1 mm/min)demonstrated intermediate behavior(∼226 MPa,∼17.7%).These variations were primarily attributed to differences in c-axis orientations,particularly their alignment with respect to the normal direction(ND)and their slight deviation from the extrusion direction(ED).Microstructural analysis revealed that distinct DRX mechanisms were activated under different extrusion conditions.P1 predominantly exhibited twinning-induced dynamic recrystallization(TDRX)and continuous dynamic recrystallization(CDRX),whereas P3 primarily showed CDRX and discontinuous dynamic recrystallization(DDRX).These DRX mechanisms,in combination with the activated slip systems governed by the evolving local stress state,collectively contributed to orientation rotation and texture development.During the early stage of extrusion,tensile strain along the ED promoted basalslip,rotating the c-axes toward the ND.As deformation progressed,compressive strain along the ND became dominant.In P1,basalslip remained active,aligning the c-axes along the ND and forming a smaller angle with the ED.In contrast,P3 exhibited predominant pyramidal<c+a>slip,resulting in a pronounced deviation of the c-axes from the ND and a slightly larger angle relative to the ED.The P2 sample exhibited a transitional texture state between those of P1 and P3.
基金supported by the National Natural Science Foundation of China(22108306,22478432 and 22406191)Taishan Scholars Program of Shandong Province(tsqn201909065)the Natural Science Foundation of Shandong Province(ZR2024JQ004,ZR2021YQ15)。
文摘The development of atomically dispersed platinum-based catalysts with high performance and welldefined active site structures is crucial for the commercialization of water electrolysis for hydrogen production.Herein,we propose a coordination dual-shell synergistic regulation mechanism of coal pitchderived carbon-supported single atom Pt-N_(x)O_(y)-S_(1)catalytic sites by a self-assembly-pyrolysis strategy for promoting hydrogen evolution reaction(HER).The Pt-N_(3)O1-S_(1)sites exhibited the highest HER performance,with an overpotential of 92 mV at a current density of 400 mA cm^(-2).At 50 mV,the turnover frequency was 34.04 s^(-1)and the mass activity was 22.83 A mg_(Pt)^(-l),which is 63.4 times that of the 20%Pt/C catalyst.Theoretical calculations revealed that the coordination dual-shell impacts the electronic structure of the Pt atoms and the adsorption strength towards reactants synergistically.The S atoms in the second coordination shell weakened the strength of Pt-N first shell,resulting the more surface valence electrons around Pt atoms,exhibiting the most suitable adsorption free energy and enhancing the adsorption of H^(+)on Pt-N_(3)O_(1)-S_(1)sites,thus enhancing the electrocatalytic HER process by promoting Volmer step.This work reveals that coordination dual-shell synergistic regulation is an effective strategy for enhancing the electrocatalytic reaction process.
基金Funded by the Breeding Project of Anhui Polytechnic University(No.2019YQQ027)the Scientific Research Foundation of Anhui Polytechnic University(No.xjky2022016)+1 种基金the Open Research Found of Anhui Key Laboratory of High-performance Non-ferrous Metal Materials(No.YSJS-2023-07)the Innovative Entrepreneurship Training Program for College Students in Anhui Province(No.S202210363391)。
文摘A series of CoS_(2-x)Se_(x)(x=0.05,0.1,0.2,0.3,and 2)composite catalysts were synthesized on carbon fiber paper via the hydrothermal method with Se doping.By precisely controlling the reaction temperature and Se doping level,a hollow spherical catalyst structure composed of CoSSe was successfully synthesized,which exhibited exceptional activity for hydrogen evolution in acidic solutions.The influences of Se doping on the microstructure and catalytic mechanism of hydrogen evolution reaction(HER)of these composites were systematically investigated.The experimental results reveal that the hollow spherical sample displays an overpotential value of 143 mV along with a Tafel slope value of 69.8 mV·dec^(-1)at a current density of 10 mA·cm^(-2)in an acid aqueous solution.Furthermore,it demonstrates remarkable cycling stability after undergoing 3000 cycles.The comprehensive analysis indicates that Se doping optimizes the electronic structure and enhances conductivity,meanwhile the unique hollow spherical architecture increases active sites for HER and significantly improves overall electrocatalytic performance.
基金supported by the Start-Up Research Funding of Fujian Normal University(No.Y0720326K13)the National Natural Science Foundation of China(Nos.22103035 and 22033005)+2 种基金the National Key R&D Program of China(No.2022YFA1503900)Shenzhen Science and Technology Program(No.RCYX20231211090357078)Guangdong Provincial Key Laboratory of Catalysis(No.2020B121201002).
文摘Atomically precise palladium(Pd)clusters are emerging as versatile nanomaterials with applications in catalysis and biomedicine.This study explores the synthesis,structure evolution,and catalytic properties of Pd clusters stabilized by cyclohexanethiol(HSC_(6)H_(11))ligands.Using electrospray ionization mass spectrometry(ESI-MS)and single-crystal X-ray diffraction(SXRD),structures of the Pd clusters ranging from Pd4(SC_(6)H_(11))8 to Pd18(SC_(6)H_(11))36 were determined.This analysis revealed a structure evolution from polygonal to elliptical geometries of the PdnS2n frameworks as the cluster size increased.UV-Vis-NIR spectroscopy,combined with quantum chemical calculations,elucidated changes in the electronic structure of the clusters.Catalytic studies on the Sonogashira cross-coupling reactions demonstrated a size-dependent decline in activity attributed to variations in structural arrangements and electronic properties.Mechanistic insights proposed a distinctive Pd(Ⅱ)-Pd(Ⅳ)catalytic cycle.This research underscores how ligands and cluster size influence the structures and properties of Pd clusters,offering valuable insights for the future design and application of Pd clusters in advanced catalysis and beyond.
基金supported by the National Natural Science Foundation of China(Nos.U2030206,12104022,52271014 and 22075003)the Presidential Foundation of CAEP(No.YZJJZL2023173)Sichuan Science and Technology Program(No.2021YFH0092).
文摘Li/MnO_(2) primary batteries are widely used in industry for their high specific capacity and safety.However,a deep comprehension of the Li^(+)insertion mechanism and the high self-discharge rate of the batteries is still needed.Here,the storage mechanism of Li^(+)in the tunnel structure of MnO_(2) as well as the dissolution and migration of Mn-ions were investigated based on multi-scale approaches.The Li/Mn ratio(at%)is determined at about 0.82 when the discharge voltage decreases to 2 V.The limited Li-ions transport rate in the bulk MnO_(2) restrains the reduction reaction,resulting in a low practical specific capacity.Moreover,utilizing spherical aberration-corrected transmission electron microscopy(TEM)coupled with electron energy loss spectroscopy(EELS),the presence of a mixed valence state layer of Mn^(2+)/Mn^(3+)/Mn^(4+)on the surface of the original 20 nm MnO_(2) particles was identified,which could contribute to the initial dissolution of Mn-ions.The battery separator exhibited channels for Mn-ions migration and diffusion and aggregated Mn particles.We put forward the discharge and degradation route in the ways of Mn-ions trajectories,and our findings provide a deep understanding of the high self-discharge rates and the capacity decay of Li-Mn primary batteries.
基金funded by the Thai Research Fund (Contract No.MRG5280215)the Royal Golden Jubilee Ph.D. Program (Grant No.PHD/0134/2551)
文摘Semi-solid metal processing is being developed in die casting applications to give several cost benefits. To efficiently apply this emerging technology, it is important to understand the evolution of microstructure in semi-solid slurries for the control of the theological behavior in semi-solid state. An experimental apparatus was developed which can capture the grain structure at different times at early stages to understand how the semi-solid structure evolves. In this technique, semi-solid slurry was produced by injecting fine gas bubbles into the melt through a graphite diffuser during solidification. Then, a copper quenching mold was used to draw some semi-solid slurry into a thin channel. The semi-solid slurry was then rapidly frozen in the channel giving the microstructure of the slurry at the desired time. Samples of semi-solid 356 aluminum alloy were taken at different gas injection times of 1, 5, 10, 15, 20, 30, 35, 40, and 45 s. Analysis of the microstructure suggests that the fragmentation by remelting mechanism should be responsible for the formation of globular structure in this rheocasting process.
基金Project(51575127)supported by the National Natural Science Foundation of China
文摘Cylindrical samples of Ni-based GH4037 alloy were compressed at solid temperatures(1200,1250 and 1300℃) and semi-solid temperatures(1340,1350,1360,1370 and 1380℃) with different strain rates of 0.01,0.1 and 1 s-1.High temperature deformation behavior and microstructure evolution of GH4037 alloy were investigated.The results indicated that flow stress decreased rapidly at semi-solid temperatures compared to that at solid temperatures.Besides,the flow stress continued to increase after reaching the initial peak stress at semi-solid temperatures when the strain rate was 1 s-1.With increasing the deformation temperature,the size of initial solid grains and recrystallized grains increased.At semi-solid temperatures,the grains were equiaxed,and liquid phase existed at the grain boundaries and inside the grains.Discontinuous dynamic recrystallization(DDRX) characterized by grain boundary bulging was the main nucleation mechanism for GH4037 alloy.
基金Project(2006CB605203) supported by the National Basic Research Program of China
文摘The self-developed taper barrel rheomoulding (TBR) machine for light alloy semi-solid slurry preparation was introduced.The semi-solid slurry was obtained from the intense shearing turbulence of the alloy melt in the cause of solidification, which was further caused by the relative rotation of the internal and external taper barrel whose surface contained wale and groove.The heat transmission model of TBR process, the flow rules and the shearing model of the alloy melt were deduced.Taking A365 as experimental material, the microstructure evolution rules under different slurry preparation processes were analyzed.The results show that decreasing the pouring temperature of A365 alloy melt properly or increasing the shearing rate helps to obtain ideal semi-solid microstructure with the primary particle size of about 70 μm and the shape factor of above 0.8.
基金financially supported by the National Natural Science Foundations of China(51464032)
文摘The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of ZC61 magnesium alloy were investigated by metal mold casting and semi-solid isothermal heat treatment. The results show that the addition of Cr can refine the α-Mg phase without generating a new phase, noticeably change the eutectic phase, and decrease the average size of solid particles at the same isothermal heat treatment conditions. Non-dendritic microstructures of all alloys are constituted of α_1-Mg phases, α_2-Mg phases and eutectic phases after water quenching. With isothermal temperature increased or holding time prolonged, the eutectic microstructure(α-Mg+MgZn_2+CuMgZn) at the grain boundaries in as-cast alloy is melted preferentially and then turned into semi-solid non-dendritic microstructure by processes of initial coarsening, microstructure separation, spheroidizing and final coarsening. Especially when the ZC61-0.1 Cr alloy was treated at 585 ℃ for 30 min, the ideal non-dendritic microstructure can be obtained, and the corresponding solid particle size and shape factor were 37.5 μm and 1.33, respectively. The coarsening process of solid α-Mg phase at higher temperature or longer time, which is affected by both combining growth and Ostwald ripening mechanism, is refrained when Cr is added to the ZC61 alloy.
基金Projects(2006BA104B04-1,2006BAE04B07-3)supported by the National Science and Technology Supporting Program of ChinaProject(2007KZ05)supported by the Science and Technology Supporting Project of Changchun City,China+1 种基金Project(2008)supported by the Open Subject of State Key Laboratory of Rare Earth Resource Utilization,ChinaProject supported by the"985 Project"of Jilin University,China
文摘A new Mg-14Al-0.5Mn alloy that exhibits a wide solidification range and sufficient fluidity for semi-solid forming was designed. And the rnicrostructure evolution of semi-solid Mg-14Al-0.5Mn alloy during isothermal heat treatment was investigated. The mechanism of the microstructure evolution and the processing conditions for isothermal heat treatment were also discussed. The results show that the microstructures of cast alloys consist of α-Mg,β-Mg17Al12 and a small amount of Al-Mn compounds. After holding at 520 ℃ for 3 min, the phases of β-Mg17Al12 and eutectic mixtures in the Mg-14Al-0.5Mn alloy melt and the microstructures of α-Mg change from developed dendrites to irregular solid particles. With increasing the isothermal time, the amount of liquid increases, and the solid particles grow large and become spherical. When the holding time lasts for 20 min or even longer, the solid and liquid phases achieve a state of dynamic equilibrium.
