The dramatic temperature-dependence of liquids dynamics has attracted considerable scientific interests and efforts in the past decades, but the physics of which remains elusive. In addition to temperature, some other...The dramatic temperature-dependence of liquids dynamics has attracted considerable scientific interests and efforts in the past decades, but the physics of which remains elusive. In addition to temperature, some other parameters, such as pressure, loading and size, can also tune the liquid dynamics and induce glass transition, which makes the situation more complicated. Here, we performed molecular dynamics simulations for Ni_(50)Zr_(50) bulk liquid and nanodroplet to study the dynamics evolution in the complex multivariate phase space, especially along the isotherm with the change of pressure or droplet size. It is found that the short-time Debye–Waller factor universally determines the long-time relaxation dynamics no matter how the temperature, pressure or size changes. The basic correlation even holds at the local atomic scale. This finding provides general understanding of the microscopic mechanism of dynamic arrest and dynamic heterogeneity.展开更多
Understanding mechanical relaxation, such as primary（α） and secondary（β） relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses....Understanding mechanical relaxation, such as primary（α） and secondary（β） relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses. At a fundamental level, relaxation, plastic deformation, glass transition, and crystallization of metallic glasses are intimately linked to each other, which can be related to atomic packing, inter-atomic diffusion, and cooperative atom movement. Conceptually, βrelaxation is usually associated with structural heterogeneities intrinsic to metallic glasses. However, the details of such structural heterogeneities, being masked by the meta-stable disordered long-range structure, are yet to be understood. In this paper, we briefly review the recent experimental and simulation results that were attempted to elucidate structural heterogeneities in metallic glasses within the framework of β relaxation. In particular, we will discuss the correlation amongβ relaxation, structural heterogeneity, and mechanical properties of metallic glasses.展开更多
Metallic glasses are spatially heterogeneous at the nanometer scale.However,the effects of external excitation on their structural and mechanical heterogeneity and the correlation to their properties are still unresol...Metallic glasses are spatially heterogeneous at the nanometer scale.However,the effects of external excitation on their structural and mechanical heterogeneity and the correlation to their properties are still unresolved.Nanoindentation,atomic force microscopy(AFM) and high-resolution transmis sion elec tron micro scopy(HRTEM) were carried out to explore the effects of cryogenic thermal cycling(CTC) on mechanical/structural heterogeneity,nano sc ale creep deformation and optical properties of nano structured metallic glass thin films(MGTFs).The results indicate that CTC treatment alters the distribution fluctuations of hardness/modulus and energy dissipation and results in an increase-then-decrease variation in mechanical heterogeneity.By applying Maxwell-Voigt model,it can be shown that CTC treatment results in a remarkable activation of more defects with longer relaxation time in soft regions but has only a slight effect on defects in hard regions.In addition,CTC treatment increases the transition time from primary-state stage to steady-state stage during creep deformation.The enhanced optical reflectivity of the MGTFs after 15 thermal cycles can be attributed to increased aggregation of Cu and Ni elements.The results of this study shed new light on understanding mechanical/structural heterogeneity and its influence on nanoscale creep deformation and optical characteristics of nanostructured MGTFs,and facilitate the design of high-performance nanostructured MGTFs.展开更多
Despite the great efforts dedicated to metallic glasses （MGs）, their structure still remains a mystery to be understood. With comparison to the existing mJciomechanical models, such as the free-volume and shear tran...Despite the great efforts dedicated to metallic glasses （MGs）, their structure still remains a mystery to be understood. With comparison to the existing mJciomechanical models, such as the free-volume and shear transformation zone （STZ） models, we first discuss in this article our recently proposed ＇core-shell＇ model, which contains a solid-like matrix and liquid-like inclusions. This serves as the theoretical basis to understand the structural heterogeneity in MGs in our analytical framework. After that, a scanning ultrafast nanoindentation technique is used to map out the structure heterogeneity in a Zr-based bulk metallic glass （BMG）. With these ongoing research efforts, we hope that more research work could be stimulated in the pursuit of the structure-property relation in MGs.展开更多
Noble metals have been widely used as heterogeneous catalysts because they exhibit high activity and selectivity for many reactions of both academic and industrial interest.The introduction of light atomic species(e.g...Noble metals have been widely used as heterogeneous catalysts because they exhibit high activity and selectivity for many reactions of both academic and industrial interest.The introduction of light atomic species(e.g.,H,B,C,and N)into noble metal lattices plays an important role in optimizing catalytic performance by modulating structural and electronic properties.In this review,we present a general overview of the recent advances in the modification of noble metals with light alloying elements for various catalytic reactions,particularly for energy‐related applications.We summarize the types,location,concentration,and ordering degree of light atoms as major factors in the performance of noble metal‐based catalysts,with emphasis on how they can be rationally controlled to promote activity and selectivity.We then summarize the synthetic strategies developed to incorporate light elements and highlight the theoretical and experimental methods for understanding the alloying effects.We further focus on the wide usage of noble metal‐based catalysts modified with different light alloying atoms and attempt to correlate the structural features with their catalytic performances.Finally,we discuss current challenges and future perspectives regarding the development of highly efficient noble metal‐based catalysts modified with light elements.展开更多
A combinatorial high-throughput experiment(HTE)was used to optimize composition and process of nickel-saving cryogenic steel.A gradient temperature heat treatment method with a high linear distribution of heat treatme...A combinatorial high-throughput experiment(HTE)was used to optimize composition and process of nickel-saving cryogenic steel.A gradient temperature heat treatment method with a high linear distribution of heat treatment temperature using customized graphite sleeve direct current heating was used in the combinatorial HTE,which enhanced the richness of the sample library for the single preparation of the 10^(2) level component process variables.Cryogenic steel with excellent mechanical properties was optimized using this combinatorial HTE,and the Ni content was reduced from the traditional 9 to 5.6 wt.%by using Mn instead of Ni.The heterogeneous structure architecture strategy and strengthening and toughening mechanism of the harmonic structure induced by intrinsic heat treatment of additive manufacturing were revealed.Taking the composition process optimization of Ni-saving cryogenic steel as an example,the boosting ability of combinatorial HTE in the research and development of new metal materials was proposed.展开更多
The atomic structure and associated deformation behavior of metallic glasses(MGs)have been long standing issues.Although recent computational/experimental results indicate that the structure of MGs is heterogeneous at...The atomic structure and associated deformation behavior of metallic glasses(MGs)have been long standing issues.Although recent computational/experimental results indicate that the structure of MGs is heterogeneous at the nano scale,the fundamental knowledge of the atomic basis for such structural heterogeneity and its impact on the overall properties of MGs is still lacking.We reviewed recent research on unraveling the structure heterogeneity in MGs,with emphases on the use of dynamic atomic force microscopy,the characterization of glass anelasticity by nanoindentation,and the establishment of numerous correlations with structural heterogeneity.展开更多
The effects of cryogenic thermal cycling on deformation behaviour and structural variation of{[(Fe_(0.5)Co_(0.5))_(0.75)B_(0.2)Si_(0.05)]_(96)Nb_(4)}_(99.9)Cu_(0.1) bulk metallic glass(BMG)were studied and compared wi...The effects of cryogenic thermal cycling on deformation behaviour and structural variation of{[(Fe_(0.5)Co_(0.5))_(0.75)B_(0.2)Si_(0.05)]_(96)Nb_(4)}_(99.9)Cu_(0.1) bulk metallic glass(BMG)were studied and compared with Cufree[(Fe_(0.5)Co_(0.5))_(0.75)B_(0.2)Si_(0.05)]_(96)Nb_(4) BMG.After thermal-cycled treatment between 393 K and cryogenic temperature,the{[(Fe_(0.5)Co_(0.5))_(0.75)B_(0.2)Si_(0.05)]_(96)Nb_(4)}_(99.9)Cu_(0.1)BMG obtained a plastic strain of 7.4%combined with a high yield strength of 4350 MPa.The excellent soft magnetic properties were maintained after CTC treatment.The minor addition of Cu element results in an initial nano-sized heterogeneity in the matrix,which facilitates the rejuvenation process during thermal cycling,and brings to a low optimal thermal temperature of 393 K,making the{[(Fe_(0.5)Co_(0.5))_(0.75)B_(0.2)Si_(0.05)]_(96)Nb_(4)}_(99.9)Cu_(0.1) BMG more attractive in industrial application.During thermal cycling,the formation of more soft regions leads to the increase of structural heterogeneities,which is beneficial to the initiation of shear transition zones and the formation of multiple shear bands,and thus results in the enhancement of plasticity.This study links the subtle variation of specific structure with macroscopic mechanical properties,and provides a new insight of composition selection for cryogenic thermal cycling treatment.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No.52031016)。
文摘The dramatic temperature-dependence of liquids dynamics has attracted considerable scientific interests and efforts in the past decades, but the physics of which remains elusive. In addition to temperature, some other parameters, such as pressure, loading and size, can also tune the liquid dynamics and induce glass transition, which makes the situation more complicated. Here, we performed molecular dynamics simulations for Ni_(50)Zr_(50) bulk liquid and nanodroplet to study the dynamics evolution in the complex multivariate phase space, especially along the isotherm with the change of pressure or droplet size. It is found that the short-time Debye–Waller factor universally determines the long-time relaxation dynamics no matter how the temperature, pressure or size changes. The basic correlation even holds at the local atomic scale. This finding provides general understanding of the microscopic mechanism of dynamic arrest and dynamic heterogeneity.
基金supported by the National Natural Science Foundation of China(Grant Nos.51401192 and 51611130120)the Natural Science Foundation of Shaanxi Province,China(Grant No.2016JM5009)+5 种基金the Fundamental Research Funds for the Central Universities of China(Grant Nos.3102015ZY027 and 3102015BJ(Ⅱ)JGZ019)the Aeronautical Science Foundation of China(Grant No.2015ZF53072)supported by the Hong Kong Scholar Program of China(Grant No.XJ2015056)the support of MINECO(Grant No.FIS2014-54734-P)Generalitat de Catalunya(Grant No.2014SGR00581)supported by the Research Grant Council,the Hong Kong City of China,through the General Research Fund(Grant No.City U11214914)
文摘Understanding mechanical relaxation, such as primary（α） and secondary（β） relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses. At a fundamental level, relaxation, plastic deformation, glass transition, and crystallization of metallic glasses are intimately linked to each other, which can be related to atomic packing, inter-atomic diffusion, and cooperative atom movement. Conceptually, βrelaxation is usually associated with structural heterogeneities intrinsic to metallic glasses. However, the details of such structural heterogeneities, being masked by the meta-stable disordered long-range structure, are yet to be understood. In this paper, we briefly review the recent experimental and simulation results that were attempted to elucidate structural heterogeneities in metallic glasses within the framework of β relaxation. In particular, we will discuss the correlation amongβ relaxation, structural heterogeneity, and mechanical properties of metallic glasses.
基金financially supported by the National Natural Science Foundation of China (Nos. 51971061 and 52231005)the Natural Science Foundation of Jiangsu Province (No. BK20221474)。
文摘Metallic glasses are spatially heterogeneous at the nanometer scale.However,the effects of external excitation on their structural and mechanical heterogeneity and the correlation to their properties are still unresolved.Nanoindentation,atomic force microscopy(AFM) and high-resolution transmis sion elec tron micro scopy(HRTEM) were carried out to explore the effects of cryogenic thermal cycling(CTC) on mechanical/structural heterogeneity,nano sc ale creep deformation and optical properties of nano structured metallic glass thin films(MGTFs).The results indicate that CTC treatment alters the distribution fluctuations of hardness/modulus and energy dissipation and results in an increase-then-decrease variation in mechanical heterogeneity.By applying Maxwell-Voigt model,it can be shown that CTC treatment results in a remarkable activation of more defects with longer relaxation time in soft regions but has only a slight effect on defects in hard regions.In addition,CTC treatment increases the transition time from primary-state stage to steady-state stage during creep deformation.The enhanced optical reflectivity of the MGTFs after 15 thermal cycles can be attributed to increased aggregation of Cu and Ni elements.The results of this study shed new light on understanding mechanical/structural heterogeneity and its influence on nanoscale creep deformation and optical characteristics of nanostructured MGTFs,and facilitate the design of high-performance nanostructured MGTFs.
基金support provided by City University of Hong Kong (CityU) through the start-up grant for newly recruited faculty members (Project No. 7200303)the research of C.T. Liu is also supported by CityU (Project No. CityU117612)
文摘Despite the great efforts dedicated to metallic glasses （MGs）, their structure still remains a mystery to be understood. With comparison to the existing mJciomechanical models, such as the free-volume and shear transformation zone （STZ） models, we first discuss in this article our recently proposed ＇core-shell＇ model, which contains a solid-like matrix and liquid-like inclusions. This serves as the theoretical basis to understand the structural heterogeneity in MGs in our analytical framework. After that, a scanning ultrafast nanoindentation technique is used to map out the structure heterogeneity in a Zr-based bulk metallic glass （BMG）. With these ongoing research efforts, we hope that more research work could be stimulated in the pursuit of the structure-property relation in MGs.
文摘Noble metals have been widely used as heterogeneous catalysts because they exhibit high activity and selectivity for many reactions of both academic and industrial interest.The introduction of light atomic species(e.g.,H,B,C,and N)into noble metal lattices plays an important role in optimizing catalytic performance by modulating structural and electronic properties.In this review,we present a general overview of the recent advances in the modification of noble metals with light alloying elements for various catalytic reactions,particularly for energy‐related applications.We summarize the types,location,concentration,and ordering degree of light atoms as major factors in the performance of noble metal‐based catalysts,with emphasis on how they can be rationally controlled to promote activity and selectivity.We then summarize the synthetic strategies developed to incorporate light elements and highlight the theoretical and experimental methods for understanding the alloying effects.We further focus on the wide usage of noble metal‐based catalysts modified with different light alloying atoms and attempt to correlate the structural features with their catalytic performances.Finally,we discuss current challenges and future perspectives regarding the development of highly efficient noble metal‐based catalysts modified with light elements.
基金the financial support of the National KeyR&DProgram of China(No.2021YFB3702401)Major Program of the National Natural Science Foundation of China(No.52293394)the National Natural Science Foundation of China(No.51831002).
文摘A combinatorial high-throughput experiment(HTE)was used to optimize composition and process of nickel-saving cryogenic steel.A gradient temperature heat treatment method with a high linear distribution of heat treatment temperature using customized graphite sleeve direct current heating was used in the combinatorial HTE,which enhanced the richness of the sample library for the single preparation of the 10^(2) level component process variables.Cryogenic steel with excellent mechanical properties was optimized using this combinatorial HTE,and the Ni content was reduced from the traditional 9 to 5.6 wt.%by using Mn instead of Ni.The heterogeneous structure architecture strategy and strengthening and toughening mechanism of the harmonic structure induced by intrinsic heat treatment of additive manufacturing were revealed.Taking the composition process optimization of Ni-saving cryogenic steel as an example,the boosting ability of combinatorial HTE in the research and development of new metal materials was proposed.
基金supported by the Research Grant Council(RGC)of the government of Hong Kong through the General Research Fund(Grant No.City U 117612)GRC(Grant No.City U 530711)
文摘The atomic structure and associated deformation behavior of metallic glasses(MGs)have been long standing issues.Although recent computational/experimental results indicate that the structure of MGs is heterogeneous at the nano scale,the fundamental knowledge of the atomic basis for such structural heterogeneity and its impact on the overall properties of MGs is still lacking.We reviewed recent research on unraveling the structure heterogeneity in MGs,with emphases on the use of dynamic atomic force microscopy,the characterization of glass anelasticity by nanoindentation,and the establishment of numerous correlations with structural heterogeneity.
基金supported by the National Natural Science Foundation of China(Grant Nos.51631003 and 51871054)the Fundamental Research Funds for the Central Universities(Grant Nos.2242019k1G005 and 2242019K40183)。
文摘The effects of cryogenic thermal cycling on deformation behaviour and structural variation of{[(Fe_(0.5)Co_(0.5))_(0.75)B_(0.2)Si_(0.05)]_(96)Nb_(4)}_(99.9)Cu_(0.1) bulk metallic glass(BMG)were studied and compared with Cufree[(Fe_(0.5)Co_(0.5))_(0.75)B_(0.2)Si_(0.05)]_(96)Nb_(4) BMG.After thermal-cycled treatment between 393 K and cryogenic temperature,the{[(Fe_(0.5)Co_(0.5))_(0.75)B_(0.2)Si_(0.05)]_(96)Nb_(4)}_(99.9)Cu_(0.1)BMG obtained a plastic strain of 7.4%combined with a high yield strength of 4350 MPa.The excellent soft magnetic properties were maintained after CTC treatment.The minor addition of Cu element results in an initial nano-sized heterogeneity in the matrix,which facilitates the rejuvenation process during thermal cycling,and brings to a low optimal thermal temperature of 393 K,making the{[(Fe_(0.5)Co_(0.5))_(0.75)B_(0.2)Si_(0.05)]_(96)Nb_(4)}_(99.9)Cu_(0.1) BMG more attractive in industrial application.During thermal cycling,the formation of more soft regions leads to the increase of structural heterogeneities,which is beneficial to the initiation of shear transition zones and the formation of multiple shear bands,and thus results in the enhancement of plasticity.This study links the subtle variation of specific structure with macroscopic mechanical properties,and provides a new insight of composition selection for cryogenic thermal cycling treatment.
