POI YOXOMETALATES have become a unique branch in chemistry because of their application in medicine and in industry as catalyst. Furthermore, polyoxometalates pose fundamental questions with respect to the elucidation...POI YOXOMETALATES have become a unique branch in chemistry because of their application in medicine and in industry as catalyst. Furthermore, polyoxometalates pose fundamental questions with respect to the elucidation of their reactivity and general coordination chemistry, of the mechanisms of interconversion of various structural types. In our investigation of展开更多
Metallic glasses(MG)have attracted considerable attention due to their high hardness,high fracture strength,and excellent corrosion resistance.However,their poor room-temperature plasticity limits their widespread app...Metallic glasses(MG)have attracted considerable attention due to their high hardness,high fracture strength,and excellent corrosion resistance.However,their poor room-temperature plasticity limits their widespread application to some extent.To address this issue,researchers have attempted to introduce crystalline phases into MG to enhance their mechanical properties.Molecular dynamics(MD)simulations are a powerful tool for investigating the properties and deformation mechanisms of amorphous/crystalline dual-phase composite materials.In this study,MD simulations were employed to explore the effect of different cooling rates on the tensile properties of B2-CuZr enhanced bulk-metallic glass composites(BMGCs).Molecular dynamics simulations were conducted on B2-CuZr enhanced BMGCs at an ambient temperature of 300 K.The results indicate that as the cooling rate decreases,from 100 K/ps,10 K/ps,1 K/ps,0.5 K/ps,the content of〈0,0,12,0〉polyhedra increases,resulting in improved mechanical strength but reduced plasticity.In this study,as the cooling rate increases from 0.5 K/ps to 100 K/ps,the deformation strain increases from ε=0.407 to ε=0.466.However,the specimens with a cooling rate of 1 K/ps display notably better plasticity,deviating from the trend.This enhancement in plasticity is attributed to the increased presence of〈0,2,8,5〉polyhedra in the 1 K/ps sample.The findings of this study provide valuable insights for the design and fabrication of high-performance metallic glass materials.展开更多
Five-fold symmetric diamond crystals（FSDCs） were synthesized by hot filament chemical vapour deposition（HFCVD） methods. Their surface morphologies and defects were characterised by scanning electron microscopy（SE...Five-fold symmetric diamond crystals（FSDCs） were synthesized by hot filament chemical vapour deposition（HFCVD） methods. Their surface morphologies and defects were characterised by scanning electron microscopy（SEM）. From the perspective of nucleation-growth, a growth mechanism for icosahedral and other five-fold symmetric diamond crystals was discussed. Computer modelling was also carried out. The results show that the dodecahedrane（C20H20） molecule is proposed as a nucleus for the growth of icosahedral diamond crystals（IDCs）, wherein the 20 {111} surface planes develop orthogonal to the direction of the original 20 C—H bonds by sequential H abstraction and CH3 addition reactions. IDC can be pictured as an assembly of isosceles tetrahedra, with each tetrahedron contributing a {111} plane to the surface of the IDC and the remainder of the tetrahedral surfaces forming twin planes with neighbouring tetrahedra. The small mismatch（1.44°） between the {111} surface dihedral angle of a perfect icosahedron and that of a twinned icosahedron reveals itself via twin planes in the IDC grain. The modelling suggests how the relief of strain induced by this distortion could lead to the formation of defects such as concave pentagonal cavities at vertices and grooves along the grain edges that accord well with those observed experimentally. Similar arguments based on growth from the hexacyclo pentadecane（C15H20） nucleus can also account for the observed formation of star and rod shaped FSDCs, and some of their more obvious morphological defects.展开更多
The rapid solidification processes of liquid Cu56Zr44 alloys at different cooling rates （γ） were simulated by a molecular dynamics （MD） method. In order to assess the influence of cooling rate on the clustering t...The rapid solidification processes of liquid Cu56Zr44 alloys at different cooling rates （γ） were simulated by a molecular dynamics （MD） method. In order to assess the influence of cooling rate on the clustering tendency and degree towards icosahedrons, a ten-indices＇ cluster-type index method was suggested to characterize the local atomic structures in the super-cooled liquid and the rapidly solidified solid. And their clustering and ordering degrees as well as the packing density of ieosahedral clusters were also evaluated by an icosahedral clustering degree （fI）, the chemical order parameter （ηαβ） and densification coefficients （D0, DI and DIS）, respectively. Results show that the main local atomic configurations in Cu56Zr44 alloy system are Z12 clusters centered by Cu, and most of which are （12 0 12 0 0 0 0 0 0 0） standard icosahedra and （12 0 8 0 0 0 2 2 0 0） as well as （12 2 8 2 0 0 0 0 0 0） defective icosahedra. Below glass transition temperature （Tg）, these icosahedral clusters will be coalesced to various icosahedral medium-range orders （IMROs） by IS linkages, namely, icosahedral bond, and their number N, size n, order parameter ηαβ as well as spatial distributions vary with y. As the cooling rate exceeds the critical value （γc） at which a glassy transition can take place, a lower cooling rate, e.g., γ1=10^1K/ns, is demonstrated to be favorable to uplift the number of icosahedra and enlarge the size of IMROs compared with the higher cooling rates, e.g., γ5=10^5 K/ns, and their packing density and clustering degree towards icosahedra in the rapidly solidified solid can also benefit from the slow cooling process.展开更多
文摘POI YOXOMETALATES have become a unique branch in chemistry because of their application in medicine and in industry as catalyst. Furthermore, polyoxometalates pose fundamental questions with respect to the elucidation of their reactivity and general coordination chemistry, of the mechanisms of interconversion of various structural types. In our investigation of
基金supported by the National Natural Science Foundation of China(Grant No.52471005)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2024A1515010878)。
文摘Metallic glasses(MG)have attracted considerable attention due to their high hardness,high fracture strength,and excellent corrosion resistance.However,their poor room-temperature plasticity limits their widespread application to some extent.To address this issue,researchers have attempted to introduce crystalline phases into MG to enhance their mechanical properties.Molecular dynamics(MD)simulations are a powerful tool for investigating the properties and deformation mechanisms of amorphous/crystalline dual-phase composite materials.In this study,MD simulations were employed to explore the effect of different cooling rates on the tensile properties of B2-CuZr enhanced bulk-metallic glass composites(BMGCs).Molecular dynamics simulations were conducted on B2-CuZr enhanced BMGCs at an ambient temperature of 300 K.The results indicate that as the cooling rate decreases,from 100 K/ps,10 K/ps,1 K/ps,0.5 K/ps,the content of〈0,0,12,0〉polyhedra increases,resulting in improved mechanical strength but reduced plasticity.In this study,as the cooling rate increases from 0.5 K/ps to 100 K/ps,the deformation strain increases from ε=0.407 to ε=0.466.However,the specimens with a cooling rate of 1 K/ps display notably better plasticity,deviating from the trend.This enhancement in plasticity is attributed to the increased presence of〈0,2,8,5〉polyhedra in the 1 K/ps sample.The findings of this study provide valuable insights for the design and fabrication of high-performance metallic glass materials.
基金Projects(51301211,21271188)supported by the National Natural Science Foundation of ChinaProject(2012M521540)supported by the China Postdoctoral Science Foundation+2 种基金Project(2013RS4027)supported by the Postdoctoral Science Foundation of Hunan Province,ChinaProject(20110933K)supported by the Open Foundation of the State Key Laboratory of Powder Metallurgy,ChinaProject supported by the Open-End Fund for Valuable and Precision Instruments of Central South University,China
文摘Five-fold symmetric diamond crystals（FSDCs） were synthesized by hot filament chemical vapour deposition（HFCVD） methods. Their surface morphologies and defects were characterised by scanning electron microscopy（SEM）. From the perspective of nucleation-growth, a growth mechanism for icosahedral and other five-fold symmetric diamond crystals was discussed. Computer modelling was also carried out. The results show that the dodecahedrane（C20H20） molecule is proposed as a nucleus for the growth of icosahedral diamond crystals（IDCs）, wherein the 20 {111} surface planes develop orthogonal to the direction of the original 20 C—H bonds by sequential H abstraction and CH3 addition reactions. IDC can be pictured as an assembly of isosceles tetrahedra, with each tetrahedron contributing a {111} plane to the surface of the IDC and the remainder of the tetrahedral surfaces forming twin planes with neighbouring tetrahedra. The small mismatch（1.44°） between the {111} surface dihedral angle of a perfect icosahedron and that of a twinned icosahedron reveals itself via twin planes in the IDC grain. The modelling suggests how the relief of strain induced by this distortion could lead to the formation of defects such as concave pentagonal cavities at vertices and grooves along the grain edges that accord well with those observed experimentally. Similar arguments based on growth from the hexacyclo pentadecane（C15H20） nucleus can also account for the observed formation of star and rod shaped FSDCs, and some of their more obvious morphological defects.
基金Project(51071065)supported by the National Natural Science Foundation of ChinaProject(20100161110001)supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘The rapid solidification processes of liquid Cu56Zr44 alloys at different cooling rates （γ） were simulated by a molecular dynamics （MD） method. In order to assess the influence of cooling rate on the clustering tendency and degree towards icosahedrons, a ten-indices＇ cluster-type index method was suggested to characterize the local atomic structures in the super-cooled liquid and the rapidly solidified solid. And their clustering and ordering degrees as well as the packing density of ieosahedral clusters were also evaluated by an icosahedral clustering degree （fI）, the chemical order parameter （ηαβ） and densification coefficients （D0, DI and DIS）, respectively. Results show that the main local atomic configurations in Cu56Zr44 alloy system are Z12 clusters centered by Cu, and most of which are （12 0 12 0 0 0 0 0 0 0） standard icosahedra and （12 0 8 0 0 0 2 2 0 0） as well as （12 2 8 2 0 0 0 0 0 0） defective icosahedra. Below glass transition temperature （Tg）, these icosahedral clusters will be coalesced to various icosahedral medium-range orders （IMROs） by IS linkages, namely, icosahedral bond, and their number N, size n, order parameter ηαβ as well as spatial distributions vary with y. As the cooling rate exceeds the critical value （γc） at which a glassy transition can take place, a lower cooling rate, e.g., γ1=10^1K/ns, is demonstrated to be favorable to uplift the number of icosahedra and enlarge the size of IMROs compared with the higher cooling rates, e.g., γ5=10^5 K/ns, and their packing density and clustering degree towards icosahedra in the rapidly solidified solid can also benefit from the slow cooling process.
