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
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
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
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
In this study,the characteristics and solidification behavior of Ti-48Al-3Nb-1.5Ta powder produced by supreme-speed plasma rotating electrode process(SS-PREP®)were investigated.The microstructure,phase and charac...In this study,the characteristics and solidification behavior of Ti-48Al-3Nb-1.5Ta powder produced by supreme-speed plasma rotating electrode process(SS-PREP®)were investigated.The microstructure,phase and characteristics were analyzed by scanning electron microscopy,X-ray diffraction and other methods.The atomization mechanism is direct drop formation.The relationship between the particle size and cooling rate is vc=3.14×10^(-7)·d^(-2)+1.18×10^(-2)·d^(3/2),and the relationship between secondary dendrite arm space and the particle size isλ=0.028d+0.11,as well as the relationship between SDAS and cooling rate isλ=4.84×10^(-5)·T^(-1.43).With increase in particle size,the surface structure gradually changes from the featureless smooth structure to dendritic and cellular dendritic morphology,and the flow ability becomes better.The carbides mainly exist within 5 nm of the surface and the oxidation layer is about 20 nm thick.Ti-48Al-3Nb-1.5Ta powder was mainly composed ofα2 phase andγphase.With increase in particle size,the content ofγphase increases,and the hardness decreases accordingly.The 106–250μm particles are composed of multiple grains with the grain size of 70–80μm.The microstructure,phase composition and hardness of different TiAl powders with the same size are similar,but the elastic modulus is different.展开更多
1.Introduction.Cold Spray(CS)is a highly advanced solid-state metal depo-sition process that was first developed in the 1980s.This innovative technique involves the high-speed(300-1200 m/s)impact deposition of micron-...1.Introduction.Cold Spray(CS)is a highly advanced solid-state metal depo-sition process that was first developed in the 1980s.This innovative technique involves the high-speed(300-1200 m/s)impact deposition of micron-sized particles(5-50μm)to fabricate coatings[1-3].CS has been extensively used in a variety of coating applications,such as aerospace,automotive,energy,medical,marine,and others,to provide protection against high temperatures,corrosion,erosion,oxidation,and chemicals[4,5].Nowadays,the technical interest in CS is twofold:(i)as a repair process for damaged components,and(ii)as a solid-state additive manufacturing process.Compared to other fusion-based additive manufacturing(AM)technologies,Cold Spray Additive Manufacturing(CSAM)is a new member of the AM family that can enable the fabrication of deposits without undergoing melting.The chemical composition has been largely preserved from the powder to the deposit due to the minimal oxidation.The significant advantages of CSAM over other additive manufacturing processes include a high production rate,unlimited deposition size,high flexibility,and suitability for repairing damaged parts.展开更多
The big-tapered profiled ring disk is a key component of engines for rockets and missiles.A new forming technology,as called spinning-rolling process,has been proposed previously for the high performance,high efficien...The big-tapered profiled ring disk is a key component of engines for rockets and missiles.A new forming technology,as called spinning-rolling process,has been proposed previously for the high performance,high efficiency and low-cost manufacturing of the component.Blank design is the key part of plastic forming process design.For spinning-rolling process,the shape and size of the blank play a crucial role in process stability,deformation behavior and dimensional accuracy.So this work proposes a blank design method to determine the geometry structure and sizes of the blank.The mathematical model for calculating the blank size has been deduced based on volume conservation and neutral layer length invariance principle.The FE simulation and corresponding trial production of an actual big-tapered profiled ring disk show that the proposed blank design method is applicative.In order to obtain a preferred blank,the influence rules of blank size determined by different deformation degrees(rolling ratio k)on the spinning-rolling process are revealed by comprehensive FE simulations.Overall considering the process stability,circularity of the deformed ring disk and forming forces,a reasonable range of deformation degree(rolling ratio k)is recommended for the blank design of the new spinning-rolling process.展开更多
The low-cost industrial application of perovskite solar cells requires an environmentally friendly and scalable fabrication process.However,achieving high-quality perovskite layers under these requirements is challeng...The low-cost industrial application of perovskite solar cells requires an environmentally friendly and scalable fabrication process.However,achieving high-quality perovskite layers under these requirements is challenging because the multi-step optimization with multiple intercorrelated experimental variables typically requires the development of a new deposition process.To address this,we propose a two-step machine learning approach for creating a new method for perovskite deposition in ambient air and antisolvent-free processing with a low-toxicity solvent triethyl phosphate(TEP).The two-step machine learning approach integrates a precursor solubility prediction model and a device-efficiency prediction model within a Bayesian optimization framework.This framework enables the information of solubility to be passed as a constraint function when optimizing the efficiency of perovskite solar cells,facilitating a quick optimization of a TEP-based,vacuum-quenching-assisted deposition in ambient air.Furthermore,the optimal precursor solution is subsequently applied to FAPbI_(3) perovskite devices,achieving a device power conversion efficiency of 24.26%under ambient conditions(23℃and~50%relative humidity).This work demonstrates the promising potential of machine learning to expedite new fabrication processes to fulfill industrial needs.展开更多
In this study,the interaction between deformation and precipitates during multiple equal channel angular pressing(ECAP)deformations and inter-pass aging combination and its effect on the mechanical properties of 7050 ...In this study,the interaction between deformation and precipitates during multiple equal channel angular pressing(ECAP)deformations and inter-pass aging combination and its effect on the mechanical properties of 7050 aluminum alloy are studied.The result show that ECAP induces numerous substructures and dislocations,effectively promoting the precipitation of theηʹphase exhibiting a bimodal structure during inter-pass aging.Following inter-pass aging and subsequent ECAP,the decrease in grain size(4.8μm)is together with the increase in dislocation density(1.24×10^(15) m^(−2))due to the pinning effect of the precipitated phase.Simultaneously,the dislocation motion causes the second phase particles to become even finer and more diffuse.The synergistic effects of precipitation strengthening,fine grain strengthening,and dislocation strengthening collectively enhance the high strength of aluminum alloys,with ultimate tensile strength and yield strength reaching approximately 610 and 565 MPa,respectively.Meanwhile,ductility remains largely unchanged,primarily due to coordinated grain boundary sliding and the uniform and fine dispersion of second phase particles.展开更多
In this study,a new linear friction welding(LFW)process,embedded LFW process,was put forward,which was mainly applied to combination manufacturing of long or overlong loadcarrying titanium alloy structural components ...In this study,a new linear friction welding(LFW)process,embedded LFW process,was put forward,which was mainly applied to combination manufacturing of long or overlong loadcarrying titanium alloy structural components in aircraft.The interfacial plastic flow behavior and bonding mechanism of this process were investigated by a developed coupling EulerianLagrangian numerical model using software ABAQUS and a novel thermo-physical simulation method with designed embedded hot compression specimen.In addition,the formation mechanism and control method of welding defects caused by uneven plastic flow were discussed.The results reveal that the plastic flow along oscillating direction of this process is even and sufficient.In the direction perpendicular to oscillation,thermo-plastic metals mainly flow downward along welding interface under coupling of shear stress and interfacial pressure,resulting in the interfacial plastic zone shown as an inverted“V”shape.The upward plastic flow in this direction is relatively weak,and only a small amount of flash is extruded from top of joint.Moreover,the wedge block and welding components at top of joint are always in un-steady friction stage,leading to nonuniform temperature field distribution and un-welded defects.According to the results of numerical simulation,high oscillating frequency combined with low pressure and small amplitude is considered as appropriate parameter selection scheme to improve the upward interfacial plastic flow at top of joint and suppress the un-welded defects.The results of thermo-physical simulation illustrate that continuous dynamic recrystallization(CDRX)induces the bonding of interface,accompanying by intense dislocation movement and creation of many low-angle grain boundaries.In the interfacial bonding area,grain orientation is random with relatively low texture density(5.0 mud)owing to CDRX.展开更多
The 6 XXX aluminum alloy is widely used in the production of automotive front crash components.Its performance is evaluated based on two key metrics:damage delay and safety reliability,which are influenced by the mate...The 6 XXX aluminum alloy is widely used in the production of automotive front crash components.Its performance is evaluated based on two key metrics:damage delay and safety reliability,which are influenced by the material’s high product of strength and elongation(PSE)and a moderate yield-to-strength ratio(YTS).This study presents an innovative approach using torsion deformation combined with shortterm aging treatment to create a gradient structure.This structure integrates gradients in plastic strain,dislocations,precipitated phases,and grain size,forming an in-situ core-shell configuration characterized by a“soft core and hard shell”.As a result,the yield strength,ultimate tensile strength,elongation,YTS,and PSE increased by 4.07%,5.72%,66.59%,−1.52%,and 76.12%,respectively,compared to the asreceived material.Its strengthening effect is significantly better than traditional T6 treatment.Notably,the formation of a gradient structure through this novel thermomechanical processing technique optimized YTS by 11.51%compared to traditional heat treatments.The significant increase in PSE is attributed to the marked improvement in elongation indicating an effective enhancement in the strength-ductility balance.This provides a promising strategy for designing and manufacturing high-performance components.展开更多
The aerospace and aviation industry has long been at the forefront of materials and processing technologies,driven by its ongoing demand for lightweight,highly reliable,and durable components.Precision manufacturing i...The aerospace and aviation industry has long been at the forefront of materials and processing technologies,driven by its ongoing demand for lightweight,highly reliable,and durable components.Precision manufacturing is a critical discipline that directly affects the performance,functionality,and safety of aircraft and aerospace vehicles.To meet the above-mentioned stringent requirements,advanced materials and cutting-edge processing technologies have evolved alongside aerospace innovations.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
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
Photo-assisted lithium–sulfur batteries(PALSBs)offer an eco-friendly solution to address the issue of sluggish reaction kinetics of conventional LSBs.However,designing an efficient photoelectrode for practical implem...Photo-assisted lithium–sulfur batteries(PALSBs)offer an eco-friendly solution to address the issue of sluggish reaction kinetics of conventional LSBs.However,designing an efficient photoelectrode for practical implementation remains a significant challenge.Herein,we construct a free-standing polymer–inorganic hybrid photoelectrode with a direct Z-scheme heterostructure to develop high-efficiency PALSBs.Specifically,polypyrrole(PPy)is in situ vapor-phase polymerized on the surface of N-doped TiO_(2) nanorods supported on carbon cloth(N-TiO_(2)/CC),thereby forming a well-defined p–n heterojunction.This architecture efficiently facilitates the carrier separation of photo-generated electron–hole pairs and significantly enhances carrier transport by creating a built-in electric field.Thus,the PPy@N-TiO_(2)/CC can simultaneously act as a photocatalyst and an electrocatalyst to accelerate the reduction and evolution of sulfur,enabling ultrafast sulfur redox dynamics,as convincingly validated by both theoretical simulations and experimental results.Consequently,the PPy@N-TiO_(2)/CC PALSB achieves a high discharge capacity of 1653 mAh g^(−1),reaching 98.7%of the theoretical value.Furthermore,5 h of photo-charging without external voltage enables the PALSB to deliver a discharge capacity of 333 mAh g^(−1),achieving dual-mode energy harvesting capabilities.This work successfully integrates solar energy conversion and storage within a rechargeable battery system,providing a promising strategy for sustainable energy storage technologies.展开更多
Although lead(Pb)-based perovskite solar cells(PSCs)have garnered intense attention for their remarkable photovoltaic conversion efficiency,their commercial process is urgently in need of an effective damage-evaluatio...Although lead(Pb)-based perovskite solar cells(PSCs)have garnered intense attention for their remarkable photovoltaic conversion efficiency,their commercial process is urgently in need of an effective damage-evaluation system for the early diagnosis of faulty PSCs.The main cause of microdamage in perovskite films is the outflow of Pb,which significantly impacts device performance.However,no reliable correlation has been established between classical damage detection techniques and Pb detection,resulting in limited detection sensitivity.Here,we report an in situ visual microdamage evaluation method of PSCs by coating the device surface with a silica gel encapsulation layer containing porphyrin molecules.This detection technology enables high selectivity and sensitivity based on the strong complexation between the porphyrin ring and trace Pb outflow from degraded PSCs.By establishing the linear relationship between the fluorescence intensity and Pb concentration in PSCs,trace Pb outflow is pinpointed and quantified with a low detection limit of 0.65μg cm^(-2).An applet is developed for the insitu visual fluorescence detection method to facilitate the continuous real-time monitoring of series-type PSCs,thereby enabling the prompt identification and replacement of damaged PSCs and ensuring the swift restoration of high efficiency.展开更多
Highly active and stable FeOOH cocatalysts are essential for achieving optimal performance of BiVO_(4)(BVO)photoanodes.Despite offering remarkable structural stability,widely used thick FeOOH cocatalysts often suffer ...Highly active and stable FeOOH cocatalysts are essential for achieving optimal performance of BiVO_(4)(BVO)photoanodes.Despite offering remarkable structural stability,widely used thick FeOOH cocatalysts often suffer from insufficient hole transport capability,which hinders the overall activity.The present study demonstrates that a simple photoetching strategy is able to introduce gradient distributed oxygen vacancies(GO_(V))in the thick FeOOH layer and significantly enhances the photogenerated holes transport dynamics.The incorporation of GO_(V)within FeOOH not only realizes the“relay transport”of photogenerated hole through the progressive upward shift of the valence band in the spatial distribution,but also provides abundant oxidation active sites by efficient hole trapping.These improvements effectively improve the oxygen evolution reaction(OER)activities and mitigate photocorrosion by the instantaneous hole extraction.Consequently,the FeOOH-GO_(V)layer enables the BVO/FeOOH-GO_(V)photoanode to achieve an impressive photocurrent density of 5.37 mA cm^(-2)and a robust operational stability up to 160 h at 1.23 VRHE,setting new benchmarks for current density and stability in FeOOH-based BVO photoanodes.This work provides an effective avenue to optimize OER cocatalysts for constructing highly efficient and stable photoelectrochemical water splitting devices.展开更多
Pb-Sn mixed perovskite solar cells(PSCs)are crucial components for realizing efficient all-perovskite tandem devices.However,their efficiency and stability are severely limited by oxidative degradation(Sn^(4+)formatio...Pb-Sn mixed perovskite solar cells(PSCs)are crucial components for realizing efficient all-perovskite tandem devices.However,their efficiency and stability are severely limited by oxidative degradation(Sn^(4+)formation)and metallic defects(Sn^(0)/Pb^(0)).In addition,the rapid and uncontrolled Sn^(2+)nucleation kinetics result in nonuniform crystallization.Herein,we introduce a natural redox shuttle glutathione(GSH)in Pb-Sn mixed PSCs,achieving regenerable antioxidation and crystallization regulation simultaneously.The reversible redox reactions between GSH and glutathione disulfide(GSSG)enable the self-healing of Sn^(4+)and Sn^(0)/Pb^(0)impurities,creating a regenerable antioxidation protective shell at the perovskite interfaces.Meanwhile,the strong coordination between GSH and perovskite regulates the crystallization process,optimizing the nucleation and crystallization kinetics.Furthermore,the GSH incorporation creates a high-quality charge separation junction at the perovskite/hole transport layer,facilitating carrier separation and extraction.The optimized Pb-Sn PSCs exhibit impressive power conversion efficiencies(PCEs)of up to 23.71%.The champion all-perovskite tandem PSCs with GSH achieve a PCE of 28.49%and retain 90%of the initial PCE after 560 h of continuous illumination.This work establishes a new nature-inspired redox shuttling strategy and elucidates its working mechanism,advancing the development of efficient and stable all-perovskite tandem solar cells.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 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financially supported by the Key R&D Program of Shaanxi(Program No.2022GY-388).
文摘In this study,the characteristics and solidification behavior of Ti-48Al-3Nb-1.5Ta powder produced by supreme-speed plasma rotating electrode process(SS-PREP®)were investigated.The microstructure,phase and characteristics were analyzed by scanning electron microscopy,X-ray diffraction and other methods.The atomization mechanism is direct drop formation.The relationship between the particle size and cooling rate is vc=3.14×10^(-7)·d^(-2)+1.18×10^(-2)·d^(3/2),and the relationship between secondary dendrite arm space and the particle size isλ=0.028d+0.11,as well as the relationship between SDAS and cooling rate isλ=4.84×10^(-5)·T^(-1.43).With increase in particle size,the surface structure gradually changes from the featureless smooth structure to dendritic and cellular dendritic morphology,and the flow ability becomes better.The carbides mainly exist within 5 nm of the surface and the oxidation layer is about 20 nm thick.Ti-48Al-3Nb-1.5Ta powder was mainly composed ofα2 phase andγphase.With increase in particle size,the content ofγphase increases,and the hardness decreases accordingly.The 106–250μm particles are composed of multiple grains with the grain size of 70–80μm.The microstructure,phase composition and hardness of different TiAl powders with the same size are similar,but the elastic modulus is different.
基金supported by the National Natural Science Foundation of China(No.52061135101 and 52001078)the German Research Foundation(DFG,No.448318292)+3 种基金the Technology Innovation Guidance Special Foundation of Shaanxi Province(No.2023GXLH-085)the Fundamental Research Funds for the Central Universities(No.D5000240161)the Project of Key areas of innovation team in Shaanxi Province(No.2024RS-CXTD-20)The author Yingchun Xie thanks the support from the National Key R&D Program(No.2023YFE0108000).
文摘1.Introduction.Cold Spray(CS)is a highly advanced solid-state metal depo-sition process that was first developed in the 1980s.This innovative technique involves the high-speed(300-1200 m/s)impact deposition of micron-sized particles(5-50μm)to fabricate coatings[1-3].CS has been extensively used in a variety of coating applications,such as aerospace,automotive,energy,medical,marine,and others,to provide protection against high temperatures,corrosion,erosion,oxidation,and chemicals[4,5].Nowadays,the technical interest in CS is twofold:(i)as a repair process for damaged components,and(ii)as a solid-state additive manufacturing process.Compared to other fusion-based additive manufacturing(AM)technologies,Cold Spray Additive Manufacturing(CSAM)is a new member of the AM family that can enable the fabrication of deposits without undergoing melting.The chemical composition has been largely preserved from the powder to the deposit due to the minimal oxidation.The significant advantages of CSAM over other additive manufacturing processes include a high production rate,unlimited deposition size,high flexibility,and suitability for repairing damaged parts.
基金the National Natural Science Foundation of China(No.52275378)the National Key Laboratory for Precision Hot Processing of Metals(6142909200208)。
文摘The big-tapered profiled ring disk is a key component of engines for rockets and missiles.A new forming technology,as called spinning-rolling process,has been proposed previously for the high performance,high efficiency and low-cost manufacturing of the component.Blank design is the key part of plastic forming process design.For spinning-rolling process,the shape and size of the blank play a crucial role in process stability,deformation behavior and dimensional accuracy.So this work proposes a blank design method to determine the geometry structure and sizes of the blank.The mathematical model for calculating the blank size has been deduced based on volume conservation and neutral layer length invariance principle.The FE simulation and corresponding trial production of an actual big-tapered profiled ring disk show that the proposed blank design method is applicative.In order to obtain a preferred blank,the influence rules of blank size determined by different deformation degrees(rolling ratio k)on the spinning-rolling process are revealed by comprehensive FE simulations.Overall considering the process stability,circularity of the deformed ring disk and forming forces,a reasonable range of deformation degree(rolling ratio k)is recommended for the blank design of the new spinning-rolling process.
基金funding support from the Ministry of Science and Technology of P.R.China under Award No.2024YFE0213600the National Natural Science Foundation of China under Award No.52433013,52103286+1 种基金the Shaanxi Bureau of Science and Technology under Award No.2022KWZ-07the"Shccig-Qinling"Program under the contract No.SMYJY202300321C。
文摘The low-cost industrial application of perovskite solar cells requires an environmentally friendly and scalable fabrication process.However,achieving high-quality perovskite layers under these requirements is challenging because the multi-step optimization with multiple intercorrelated experimental variables typically requires the development of a new deposition process.To address this,we propose a two-step machine learning approach for creating a new method for perovskite deposition in ambient air and antisolvent-free processing with a low-toxicity solvent triethyl phosphate(TEP).The two-step machine learning approach integrates a precursor solubility prediction model and a device-efficiency prediction model within a Bayesian optimization framework.This framework enables the information of solubility to be passed as a constraint function when optimizing the efficiency of perovskite solar cells,facilitating a quick optimization of a TEP-based,vacuum-quenching-assisted deposition in ambient air.Furthermore,the optimal precursor solution is subsequently applied to FAPbI_(3) perovskite devices,achieving a device power conversion efficiency of 24.26%under ambient conditions(23℃and~50%relative humidity).This work demonstrates the promising potential of machine learning to expedite new fabrication processes to fulfill industrial needs.
基金Project(52275350)supported by the National Natural Science Foundation of ChinaProject(0301006)supported by the International Cooperative Scientific Research Platform of SUES,China。
文摘In this study,the interaction between deformation and precipitates during multiple equal channel angular pressing(ECAP)deformations and inter-pass aging combination and its effect on the mechanical properties of 7050 aluminum alloy are studied.The result show that ECAP induces numerous substructures and dislocations,effectively promoting the precipitation of theηʹphase exhibiting a bimodal structure during inter-pass aging.Following inter-pass aging and subsequent ECAP,the decrease in grain size(4.8μm)is together with the increase in dislocation density(1.24×10^(15) m^(−2))due to the pinning effect of the precipitated phase.Simultaneously,the dislocation motion causes the second phase particles to become even finer and more diffuse.The synergistic effects of precipitation strengthening,fine grain strengthening,and dislocation strengthening collectively enhance the high strength of aluminum alloys,with ultimate tensile strength and yield strength reaching approximately 610 and 565 MPa,respectively.Meanwhile,ductility remains largely unchanged,primarily due to coordinated grain boundary sliding and the uniform and fine dispersion of second phase particles.
基金co-supported by the National Natural Science Foundation of China(Nos.52105411,52105400and 52305420)the China Postdoctoral Science Foundation(No.2023M742830)Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(No.CX2023008).
文摘In this study,a new linear friction welding(LFW)process,embedded LFW process,was put forward,which was mainly applied to combination manufacturing of long or overlong loadcarrying titanium alloy structural components in aircraft.The interfacial plastic flow behavior and bonding mechanism of this process were investigated by a developed coupling EulerianLagrangian numerical model using software ABAQUS and a novel thermo-physical simulation method with designed embedded hot compression specimen.In addition,the formation mechanism and control method of welding defects caused by uneven plastic flow were discussed.The results reveal that the plastic flow along oscillating direction of this process is even and sufficient.In the direction perpendicular to oscillation,thermo-plastic metals mainly flow downward along welding interface under coupling of shear stress and interfacial pressure,resulting in the interfacial plastic zone shown as an inverted“V”shape.The upward plastic flow in this direction is relatively weak,and only a small amount of flash is extruded from top of joint.Moreover,the wedge block and welding components at top of joint are always in un-steady friction stage,leading to nonuniform temperature field distribution and un-welded defects.According to the results of numerical simulation,high oscillating frequency combined with low pressure and small amplitude is considered as appropriate parameter selection scheme to improve the upward interfacial plastic flow at top of joint and suppress the un-welded defects.The results of thermo-physical simulation illustrate that continuous dynamic recrystallization(CDRX)induces the bonding of interface,accompanying by intense dislocation movement and creation of many low-angle grain boundaries.In the interfacial bonding area,grain orientation is random with relatively low texture density(5.0 mud)owing to CDRX.
基金support received from the National Key Research and Development Program of China(Grant No.2021YFB3400902)the National Natural Science Foundation of China(Grant No.51275414,52205418)+1 种基金the Fundamental Research Funds for the Central Universities with Grant No.3102015BJ(Ⅱ)ZS007the Key Research and Development Program of Shaanxi Province(No.2020ZDLGY12-07).
文摘The 6 XXX aluminum alloy is widely used in the production of automotive front crash components.Its performance is evaluated based on two key metrics:damage delay and safety reliability,which are influenced by the material’s high product of strength and elongation(PSE)and a moderate yield-to-strength ratio(YTS).This study presents an innovative approach using torsion deformation combined with shortterm aging treatment to create a gradient structure.This structure integrates gradients in plastic strain,dislocations,precipitated phases,and grain size,forming an in-situ core-shell configuration characterized by a“soft core and hard shell”.As a result,the yield strength,ultimate tensile strength,elongation,YTS,and PSE increased by 4.07%,5.72%,66.59%,−1.52%,and 76.12%,respectively,compared to the asreceived material.Its strengthening effect is significantly better than traditional T6 treatment.Notably,the formation of a gradient structure through this novel thermomechanical processing technique optimized YTS by 11.51%compared to traditional heat treatments.The significant increase in PSE is attributed to the marked improvement in elongation indicating an effective enhancement in the strength-ductility balance.This provides a promising strategy for designing and manufacturing high-performance components.
文摘The aerospace and aviation industry has long been at the forefront of materials and processing technologies,driven by its ongoing demand for lightweight,highly reliable,and durable components.Precision manufacturing is a critical discipline that directly affects the performance,functionality,and safety of aircraft and aerospace vehicles.To meet the above-mentioned stringent requirements,advanced materials and cutting-edge processing technologies have evolved alongside aerospace innovations.
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the financial support from the National Natural Science Foundation of China (22109127)the Chinese Postdoctoral Science Foundation (2021M702666)+2 种基金the Research Fund of the State Key Laboratory of Solidification Processing (NPU),China (Grant No.2023-TS-02)The financial support from the Youth Project of"Shaanxi High-level Talents Introduction Plan"the Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education) are also sincerely appreciated
文摘Photo-assisted lithium–sulfur batteries(PALSBs)offer an eco-friendly solution to address the issue of sluggish reaction kinetics of conventional LSBs.However,designing an efficient photoelectrode for practical implementation remains a significant challenge.Herein,we construct a free-standing polymer–inorganic hybrid photoelectrode with a direct Z-scheme heterostructure to develop high-efficiency PALSBs.Specifically,polypyrrole(PPy)is in situ vapor-phase polymerized on the surface of N-doped TiO_(2) nanorods supported on carbon cloth(N-TiO_(2)/CC),thereby forming a well-defined p–n heterojunction.This architecture efficiently facilitates the carrier separation of photo-generated electron–hole pairs and significantly enhances carrier transport by creating a built-in electric field.Thus,the PPy@N-TiO_(2)/CC can simultaneously act as a photocatalyst and an electrocatalyst to accelerate the reduction and evolution of sulfur,enabling ultrafast sulfur redox dynamics,as convincingly validated by both theoretical simulations and experimental results.Consequently,the PPy@N-TiO_(2)/CC PALSB achieves a high discharge capacity of 1653 mAh g^(−1),reaching 98.7%of the theoretical value.Furthermore,5 h of photo-charging without external voltage enables the PALSB to deliver a discharge capacity of 333 mAh g^(−1),achieving dual-mode energy harvesting capabilities.This work successfully integrates solar energy conversion and storage within a rechargeable battery system,providing a promising strategy for sustainable energy storage technologies.
基金financial support from the Shccig-Qinling Program(SMYJY202300294C)the Science,Technology,and Innovation Commission of Shenzhen Municipality(GJHZ20220913143204008,JCYJ20220818103417036)+1 种基金the National Natural Science Foundation of China(22261142666,52172237,52372225)the Shaanxi Science Fund for Distinguished Young Scholars(2022JC-21)。
文摘Although lead(Pb)-based perovskite solar cells(PSCs)have garnered intense attention for their remarkable photovoltaic conversion efficiency,their commercial process is urgently in need of an effective damage-evaluation system for the early diagnosis of faulty PSCs.The main cause of microdamage in perovskite films is the outflow of Pb,which significantly impacts device performance.However,no reliable correlation has been established between classical damage detection techniques and Pb detection,resulting in limited detection sensitivity.Here,we report an in situ visual microdamage evaluation method of PSCs by coating the device surface with a silica gel encapsulation layer containing porphyrin molecules.This detection technology enables high selectivity and sensitivity based on the strong complexation between the porphyrin ring and trace Pb outflow from degraded PSCs.By establishing the linear relationship between the fluorescence intensity and Pb concentration in PSCs,trace Pb outflow is pinpointed and quantified with a low detection limit of 0.65μg cm^(-2).An applet is developed for the insitu visual fluorescence detection method to facilitate the continuous real-time monitoring of series-type PSCs,thereby enabling the prompt identification and replacement of damaged PSCs and ensuring the swift restoration of high efficiency.
基金supported by the State Key Laboratory of Solidification Processing in NWPU(SKLSP202407)the National Natural Science Foundation of China(52402130)+2 种基金the Natural Science Basis Research Plan in Shaanxi Province of China(2024JC-YBQN-0384)the Shaanxi Science and Technology Innovation Team(2023-CX-TD-44)the National Natural Science Foundation of China(52301015).
文摘Highly active and stable FeOOH cocatalysts are essential for achieving optimal performance of BiVO_(4)(BVO)photoanodes.Despite offering remarkable structural stability,widely used thick FeOOH cocatalysts often suffer from insufficient hole transport capability,which hinders the overall activity.The present study demonstrates that a simple photoetching strategy is able to introduce gradient distributed oxygen vacancies(GO_(V))in the thick FeOOH layer and significantly enhances the photogenerated holes transport dynamics.The incorporation of GO_(V)within FeOOH not only realizes the“relay transport”of photogenerated hole through the progressive upward shift of the valence band in the spatial distribution,but also provides abundant oxidation active sites by efficient hole trapping.These improvements effectively improve the oxygen evolution reaction(OER)activities and mitigate photocorrosion by the instantaneous hole extraction.Consequently,the FeOOH-GO_(V)layer enables the BVO/FeOOH-GO_(V)photoanode to achieve an impressive photocurrent density of 5.37 mA cm^(-2)and a robust operational stability up to 160 h at 1.23 VRHE,setting new benchmarks for current density and stability in FeOOH-based BVO photoanodes.This work provides an effective avenue to optimize OER cocatalysts for constructing highly efficient and stable photoelectrochemical water splitting devices.
基金supported by Guangdong Basic and Applied Basic Research Foundation(2025A1515011362)the National Natural Science Foundation of China(52102304,52172238)Open Project of Shaanxi Laboratory of Aerospace Power(2021SXSYS-01-03).
文摘Pb-Sn mixed perovskite solar cells(PSCs)are crucial components for realizing efficient all-perovskite tandem devices.However,their efficiency and stability are severely limited by oxidative degradation(Sn^(4+)formation)and metallic defects(Sn^(0)/Pb^(0)).In addition,the rapid and uncontrolled Sn^(2+)nucleation kinetics result in nonuniform crystallization.Herein,we introduce a natural redox shuttle glutathione(GSH)in Pb-Sn mixed PSCs,achieving regenerable antioxidation and crystallization regulation simultaneously.The reversible redox reactions between GSH and glutathione disulfide(GSSG)enable the self-healing of Sn^(4+)and Sn^(0)/Pb^(0)impurities,creating a regenerable antioxidation protective shell at the perovskite interfaces.Meanwhile,the strong coordination between GSH and perovskite regulates the crystallization process,optimizing the nucleation and crystallization kinetics.Furthermore,the GSH incorporation creates a high-quality charge separation junction at the perovskite/hole transport layer,facilitating carrier separation and extraction.The optimized Pb-Sn PSCs exhibit impressive power conversion efficiencies(PCEs)of up to 23.71%.The champion all-perovskite tandem PSCs with GSH achieve a PCE of 28.49%and retain 90%of the initial PCE after 560 h of continuous illumination.This work establishes a new nature-inspired redox shuttling strategy and elucidates its working mechanism,advancing the development of efficient and stable all-perovskite tandem solar cells.
