1.Introduction As one of the most widely used additive manufacturing(AM)techniques,selective laser melting(SLM)is a laser-based layer-by-layer manufacturing process,which has relatively high fabrication resolution and...1.Introduction As one of the most widely used additive manufacturing(AM)techniques,selective laser melting(SLM)is a laser-based layer-by-layer manufacturing process,which has relatively high fabrication resolution and can directly form complex metal parts.During SLM,the interaction of laser with metal powder forms a tiny melt pool.Following the rapid movement of the laser,the cooling rate of the melt pool can be as high as 105-106 K s−1[1].Such a fast cool-ing rate inhibits grain growth and element segregation in the alloy,leading to a notable enhancement in strength and toughness[2].Therefore,SLM enables unlimited possibilities in the fabrication of complex parts with high performance.To date,the most extensively researched Al alloys for SLM are Al-Si alloys,such as AlSi10Mg,Al-12Si,and AlSi7Mg[2-5].展开更多
The eutectic Ag-Cu alloys exhibiting fine Ag-Cu lamellar eutectic structure formed upon rapid solidification have great potentials being used in various engineering fields.However,the desired fine primary lamellar eut...The eutectic Ag-Cu alloys exhibiting fine Ag-Cu lamellar eutectic structure formed upon rapid solidification have great potentials being used in various engineering fields.However,the desired fine primary lamellar eutectic structure(PLES)is usually replaced by a coarse anomalous eutectic structure(AES)when the undercooling prior to solidification exceeds a certain value.The forming mechanism of AES in the undercooled eutectic Ag-Cu alloy has been a controversial issue.In this work,the undercooled Ag-39.9 at.% Cu eutectic alloy is solidified under different cooling conditions by using techniques of melt fluxing and copper mold casting.The results show that the coupled eutectic growth of this alloy undergoes a transition from a slow eutectic-cellular growth(ECG)to a rapid eutectic-dendritic growth(EDG)above a undercooling of 72 K,accompanying with an abrupt change of the distribution and amount of AES in as-solidified microstructures.Two kinds of primary lamellar eutectic structures are formed by ECG and EDG during recalescence,respectively.The destabilization of PLES that causes the formation of AES is ascribed to two different mechanisms based on the microstructural examination and theoretical calculations.Below 72 K,the destabilization of PLES formed by slow ECG is caused by the mechanism of"termination migration"driven by interfacial energy.While above 72 K,the destabilization of PLES formed by rapid EDG is attributed to the unstable perturbation of interface driven by interfacial energy and solute supersaturation.展开更多
Compared to a cast AlSi10Mg alloy,a laser powder bed fused(LPBF)AlSi10Mg alloy shows superior yield strength and strain hardening capability.However,the underlying microstructure origin has not been comprehensively un...Compared to a cast AlSi10Mg alloy,a laser powder bed fused(LPBF)AlSi10Mg alloy shows superior yield strength and strain hardening capability.However,the underlying microstructure origin has not been comprehensively understood.In this work,the microstructural evolution of an LPBF AlSi10Mg alloy dur-ing tensile deformation was investigated.Synchrotron X-ray diffraction characterization shows that both stress and strain exhibit significant partition between an Al phase and a Si phase upon tensile deforma-tion.This leads to a significant strain gradient between those two phases,which is evident by the high density of dislocations in the cell boundaries of the deformed alloy.The strain gradient results in long-range internal stress,also known as back stress,in the cell boundaries,and in turn leads to enhanced strength and strain hardening in the LPBF AlSi10Mg alloy.Quantitatively analyses via loading-unloading-reloading tests show that during the tensile deformation,the back stress contributes 135 MPa to the yield strength of the alloy,which continuously increases with increasing the strain beyond the yielding point.This work illuminates the microstructural origin of the back stress in the LPBF AlSi10Mg alloy,i.e.the back stress arises from the stress/strain partition between the Al and Si phases in the cellular structures,and the back stress leads to significant strengthening of the alloy upon tensile deformation.This work may also provide guidance for manipulating the mechanical properties of additively manufactured Al-Si alloys for specific application needs.展开更多
Second-phase particle pinning has been well known as a mechanism impeding grain boundary （GB） migration, and thus, is documented as an efficient approach for stabilizing nanocrystalline （NC） materials at elevated ...Second-phase particle pinning has been well known as a mechanism impeding grain boundary （GB） migration, and thus, is documented as an efficient approach for stabilizing nanocrystalline （NC） materials at elevated temperatures. The pinning force exerted by interaction between small dispersed particles and GBs strongly depends on size and volume fraction of the particles. Since metallic oxides, e.g. Al2O3, exhibit great structural stability and high resistance against coarsening at high temperatures, they are expected as effective stabilizers for NC materials. In this work, NC composites consisting of NC Fe and Al2O3 nanoparticIes with different amounts and sizes were prepared by high energy ball milling and annealed at various temperatures （Tann） for different time periods （tann）. Microstructures of the ball milled and annealed samples were examined by X-ray diffraction and transmission electron microscopy. The results show that the addition of Al2O3 nanoparticles not only enhances the thermal stability of NC Fe grains but also reduces their coarsening rate at elevated temperatures, and reducing the particle size and/or increasing its amount enhance the stabilizing effect of the Al2O3 particles on the NC Fe grains.展开更多
TiC_(x)is an excellent composite strengthening particle and grain refiner for Al alloys.However,the stability of TiC_(x)is poor when solute Si exists in Al alloy melts,which significantly depresses its strengthening a...TiC_(x)is an excellent composite strengthening particle and grain refiner for Al alloys.However,the stability of TiC_(x)is poor when solute Si exists in Al alloy melts,which significantly depresses its strengthening and grain refining effects.In this work,the destabilization mechanisms of the TiC_(x)particles in Al-Si alloy melt with a composition of Al-7Si-7.5TiC were explored via experiments,first-principles calculations and thermodynamic calculations.The experimental results show that Si atoms diffuse into TiC_(x)and Ti atoms are released into the Al melt to form a Ti-rich transition zone during the insulation of TiC_(x)in Al-Si melt,and the TiAlySiz and Al_(4)C_(3)phases are solidified in the Ti-rich zone and at Ti-rich zone/TiC_(x)interface,respectively.The first principles calculations show that the low formation energy of C vacancies facilitates the rapid diffusion of Si atoms in TiC_(x),while the doping of Si atoms reduces the energy barrier of diffusion of Ti atoms in TiC_(x)and promotes the formation of Ti-rich zones.The thermodynamic calculations show that the wide crystallization temperature range of the destabilized product TiAlySiz phase is the key to continuous decomposition of TiC_(x)particles.In addition,the driving force of the main destabilization reaction of TiC_(x)in the Al-Si alloys is about 44 times higher than that in the Al alloys without Si addition.This indicates that the presence of solute Si remarkably promotes the subsequent decomposition process of TiC_(x)in the Al-Si alloy melts.展开更多
Microstructures of nanoporous Pd are essentially important for its physical and chemical properties.In this work,we show that the microstructures of nanoporous Pd can be tuned by adjusting compositions of the precurso...Microstructures of nanoporous Pd are essentially important for its physical and chemical properties.In this work,we show that the microstructures of nanoporous Pd can be tuned by adjusting compositions of the precursor alloys,and dealloying and heat treatment parameters.Both the ligament and pore sizes decrease with increasing the electrochemical potential upon dealloying and the concentration of noble component in the precursor alloys.Heat treatment causes coarsening of the nanoporous structure.Above a critical temperature,the nanoporous structures are subjected to significant coarsening.Below the critical temperature,surface diffusion is believed to dominate the coarsening process.Above the critical temperature,the nanoporous structure coarsens remarkably at a rather high rate,which is ascribed to a multiple-mechanism controlled process.展开更多
Inflammation in central nervous system(CNS)is one of the most severe diseases,and also plays an impellent role in some neurodegenerative diseases.Glutamate(Glu)has been considered relevant to the pathogenesis of neuro...Inflammation in central nervous system(CNS)is one of the most severe diseases,and also plays an impellent role in some neurodegenerative diseases.Glutamate(Glu)has been considered relevant to the pathogenesis of neuroinflammation.In order to diagnose neuroinflammation incipiently and precisely,we review the pathobiological events in the early stages of neuroinflammation,the interactions between Glu and neuroinflammation,and two kinds of magnetic resonance techniques of imaging Glu(chemical exchange saturation transfer and magnetic resonance spectroscopy).展开更多
基金supported by the National Natu-ral Science Foundation of China(Nos.52071262,52301197,and 52234009)the National Key Research and Development Program(No.2022YFB3404203)+3 种基金the Natural Science Basic Research Pro-gram of Shaanxi Province,China(No.2023-JC-QN-0421)the Re-search Fund of the State Key Laboratory of Solidification Processing(NPU),China(Nos.2024-ZD-06 and 2024-TS-06)the Fundamental Research Funds for the Central Universities(No.D5000240144)the Young Talent Fund of Xi’an Association for Science and Tech-nology(No.959202413014).
文摘1.Introduction As one of the most widely used additive manufacturing(AM)techniques,selective laser melting(SLM)is a laser-based layer-by-layer manufacturing process,which has relatively high fabrication resolution and can directly form complex metal parts.During SLM,the interaction of laser with metal powder forms a tiny melt pool.Following the rapid movement of the laser,the cooling rate of the melt pool can be as high as 105-106 K s−1[1].Such a fast cool-ing rate inhibits grain growth and element segregation in the alloy,leading to a notable enhancement in strength and toughness[2].Therefore,SLM enables unlimited possibilities in the fabrication of complex parts with high performance.To date,the most extensively researched Al alloys for SLM are Al-Si alloys,such as AlSi10Mg,Al-12Si,and AlSi7Mg[2-5].
基金the National Natural Science Foundation of China(Nos.51771153,51371147,51790481 and 51431008)the Innovation Guidance Support Project for Taicang Top Research Institutes(No.TC2018DYDS20)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(CX201825)。
文摘The eutectic Ag-Cu alloys exhibiting fine Ag-Cu lamellar eutectic structure formed upon rapid solidification have great potentials being used in various engineering fields.However,the desired fine primary lamellar eutectic structure(PLES)is usually replaced by a coarse anomalous eutectic structure(AES)when the undercooling prior to solidification exceeds a certain value.The forming mechanism of AES in the undercooled eutectic Ag-Cu alloy has been a controversial issue.In this work,the undercooled Ag-39.9 at.% Cu eutectic alloy is solidified under different cooling conditions by using techniques of melt fluxing and copper mold casting.The results show that the coupled eutectic growth of this alloy undergoes a transition from a slow eutectic-cellular growth(ECG)to a rapid eutectic-dendritic growth(EDG)above a undercooling of 72 K,accompanying with an abrupt change of the distribution and amount of AES in as-solidified microstructures.Two kinds of primary lamellar eutectic structures are formed by ECG and EDG during recalescence,respectively.The destabilization of PLES that causes the formation of AES is ascribed to two different mechanisms based on the microstructural examination and theoretical calculations.Below 72 K,the destabilization of PLES formed by slow ECG is caused by the mechanism of"termination migration"driven by interfacial energy.While above 72 K,the destabilization of PLES formed by rapid EDG is attributed to the unstable perturbation of interface driven by interfacial energy and solute supersaturation.
基金the National Key Research and Development Program(No.2022YFB3404203)the National Natural Science Foundation of China(Nos.52071262,52101049,52301197,52234009)+1 种基金the Qinchuangyuan"cientist+Engineer"Team Development of Shaanxi Province(No.2022KXJ-020)the Advanced Development of Aluminum Alloy Filler Materials used in welded High-end Lightweight Constructions-Research&Industrial implementation(No.2022Z109).
文摘Compared to a cast AlSi10Mg alloy,a laser powder bed fused(LPBF)AlSi10Mg alloy shows superior yield strength and strain hardening capability.However,the underlying microstructure origin has not been comprehensively understood.In this work,the microstructural evolution of an LPBF AlSi10Mg alloy dur-ing tensile deformation was investigated.Synchrotron X-ray diffraction characterization shows that both stress and strain exhibit significant partition between an Al phase and a Si phase upon tensile deforma-tion.This leads to a significant strain gradient between those two phases,which is evident by the high density of dislocations in the cell boundaries of the deformed alloy.The strain gradient results in long-range internal stress,also known as back stress,in the cell boundaries,and in turn leads to enhanced strength and strain hardening in the LPBF AlSi10Mg alloy.Quantitatively analyses via loading-unloading-reloading tests show that during the tensile deformation,the back stress contributes 135 MPa to the yield strength of the alloy,which continuously increases with increasing the strain beyond the yielding point.This work illuminates the microstructural origin of the back stress in the LPBF AlSi10Mg alloy,i.e.the back stress arises from the stress/strain partition between the Al and Si phases in the cellular structures,and the back stress leads to significant strengthening of the alloy upon tensile deformation.This work may also provide guidance for manipulating the mechanical properties of additively manufactured Al-Si alloys for specific application needs.
基金the National Key R&D Program of China (Project No. 2017YFB0703001)the National Natural Science Foundation of China (Nos. 51371147, 51101121, 51125002, 51134011, 51771153 and 51431008)+2 种基金the Research Fund of the State Key Lab. of Solidification Processing (NWPU) (No. 146-QZ2016)the Fundamental Research Funds for the Central Universities (No. 3102017jc03008)the Shaanxi Young Stars of Science and Technology (No. 2016KJXX-44) for financial supports
文摘Second-phase particle pinning has been well known as a mechanism impeding grain boundary （GB） migration, and thus, is documented as an efficient approach for stabilizing nanocrystalline （NC） materials at elevated temperatures. The pinning force exerted by interaction between small dispersed particles and GBs strongly depends on size and volume fraction of the particles. Since metallic oxides, e.g. Al2O3, exhibit great structural stability and high resistance against coarsening at high temperatures, they are expected as effective stabilizers for NC materials. In this work, NC composites consisting of NC Fe and Al2O3 nanoparticIes with different amounts and sizes were prepared by high energy ball milling and annealed at various temperatures （Tann） for different time periods （tann）. Microstructures of the ball milled and annealed samples were examined by X-ray diffraction and transmission electron microscopy. The results show that the addition of Al2O3 nanoparticles not only enhances the thermal stability of NC Fe grains but also reduces their coarsening rate at elevated temperatures, and reducing the particle size and/or increasing its amount enhance the stabilizing effect of the Al2O3 particles on the NC Fe grains.
基金the financial supported from the Key R&D Program of Shaanxi Province,China(No.2020ZDLGY13-01)the innovation team program of material developing and application of key engine components(No.K20220185)the National Natural Science Foundation of China(Nos.52101049,52234009 and 52071262).
文摘TiC_(x)is an excellent composite strengthening particle and grain refiner for Al alloys.However,the stability of TiC_(x)is poor when solute Si exists in Al alloy melts,which significantly depresses its strengthening and grain refining effects.In this work,the destabilization mechanisms of the TiC_(x)particles in Al-Si alloy melt with a composition of Al-7Si-7.5TiC were explored via experiments,first-principles calculations and thermodynamic calculations.The experimental results show that Si atoms diffuse into TiC_(x)and Ti atoms are released into the Al melt to form a Ti-rich transition zone during the insulation of TiC_(x)in Al-Si melt,and the TiAlySiz and Al_(4)C_(3)phases are solidified in the Ti-rich zone and at Ti-rich zone/TiC_(x)interface,respectively.The first principles calculations show that the low formation energy of C vacancies facilitates the rapid diffusion of Si atoms in TiC_(x),while the doping of Si atoms reduces the energy barrier of diffusion of Ti atoms in TiC_(x)and promotes the formation of Ti-rich zones.The thermodynamic calculations show that the wide crystallization temperature range of the destabilized product TiAlySiz phase is the key to continuous decomposition of TiC_(x)particles.In addition,the driving force of the main destabilization reaction of TiC_(x)in the Al-Si alloys is about 44 times higher than that in the Al alloys without Si addition.This indicates that the presence of solute Si remarkably promotes the subsequent decomposition process of TiC_(x)in the Al-Si alloy melts.
基金supported financially by the National Natural Science Foundation of China(Nos.51771153,51371147,51790481 and 51431008)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(No.CX201825)。
文摘Microstructures of nanoporous Pd are essentially important for its physical and chemical properties.In this work,we show that the microstructures of nanoporous Pd can be tuned by adjusting compositions of the precursor alloys,and dealloying and heat treatment parameters.Both the ligament and pore sizes decrease with increasing the electrochemical potential upon dealloying and the concentration of noble component in the precursor alloys.Heat treatment causes coarsening of the nanoporous structure.Above a critical temperature,the nanoporous structures are subjected to significant coarsening.Below the critical temperature,surface diffusion is believed to dominate the coarsening process.Above the critical temperature,the nanoporous structure coarsens remarkably at a rather high rate,which is ascribed to a multiple-mechanism controlled process.
基金supported in part by the National Natural Science Foundation of China(Grant No.81471730)the National High Technology Research and Development Program(863 Program)of China(Program No.2014AA021101)the Natural Science Foundation of Guangdong Province of China(Grant No.2015A030313444).
文摘Inflammation in central nervous system(CNS)is one of the most severe diseases,and also plays an impellent role in some neurodegenerative diseases.Glutamate(Glu)has been considered relevant to the pathogenesis of neuroinflammation.In order to diagnose neuroinflammation incipiently and precisely,we review the pathobiological events in the early stages of neuroinflammation,the interactions between Glu and neuroinflammation,and two kinds of magnetic resonance techniques of imaging Glu(chemical exchange saturation transfer and magnetic resonance spectroscopy).
