Molecular Dynamics (MD) simulations of siliceous FAU-type zeolite were carried out at various temperatures. to investigate its thermal behaviors. From the study. we found that pure silicon fanjasite showed different t...Molecular Dynamics (MD) simulations of siliceous FAU-type zeolite were carried out at various temperatures. to investigate its thermal behaviors. From the study. we found that pure silicon fanjasite showed different thermal behaviors below 1500K and above 1500K. its cell volume gradually shrinks with the rising of the temperature below 1500K. the cell volume of the zeolite changes little above 1500K.展开更多
High entropy alloys(HEAs)attract remarkable attention due to the excellent mechanical performance.However,the origins of their high strength and toughness compared with those of the traditional alloys are still hardly...High entropy alloys(HEAs)attract remarkable attention due to the excellent mechanical performance.However,the origins of their high strength and toughness compared with those of the traditional alloys are still hardly revealed.Here,using a microstructure-based constitutive model and molecular dynamics(MD)simulation,we investigate the unique mechanical behavior and microstructure evolution of FeCoCrNiCu HEAs during the indentation.Due to the interaction between the dislocation and solution,the high dislocation density in FeCoCrNiCu leads to strong work hardening.Plentiful slip systems are stimulated,leading to the good plasticity of FeCoCrNiCu.The plastic deformation of FeCoCrNiCu is basically affected by the motion of dislocation loops.The prismatic dislocation loops inside FeCoCrNiCu are formed by the dislocations with the Burgers vectors of a/6[112]and a/6[112],which interact with each other,and then emit along the<111>slip direction.In addition,the mechanical properties of FeCoCrNiCu HEA can be predicted by constructing the microstructure-based constitutive model,which is identified according to the evolution of the dislocation density and the stress-strain curve.Strong dislocation strengthening and remarkable lattice distortion strengthening occur in the deformation process of FeCoCrNiCu,and improve the strength.Therefore,the origins of high strength and high toughness in FeCoCrNiCu HEAs come from lattice distortion strengthening and the more activable slip systems compared with Cu.These results accelerate the discovery of HEAs with excellent mechanical properties,and provide a valuable reference for the industrial application of HEAs.展开更多
Evolution of the charged grains in a two-dimensional dusty plasma under a spatially harmonic external force,in particular,their long-time behaviors after the force has been withdrawn,is studied by using molecular dyna...Evolution of the charged grains in a two-dimensional dusty plasma under a spatially harmonic external force,in particular,their long-time behaviors after the force has been withdrawn,is studied by using molecular dynamics simulation.Under an external force and a grain–grain interaction force,initially homogeneously distributed grains can reach a quasistationary state in the form of a disk crystal.After the external force is withdrawn,the disk moves initially with its size and shape nearly unchanged until it rapidly stops moving,and eventually the disk grain rotates like a vortex.The time needed to reach the final state increases with the strength of the initial external force increasing.展开更多
The nanoparticle thermal conductivity and nanoscale thermal contact resistance were investigated by molecular dynamics(MD) simulations to further understand nanoscale porous media thermal conductivity.Macroscale porou...The nanoparticle thermal conductivity and nanoscale thermal contact resistance were investigated by molecular dynamics(MD) simulations to further understand nanoscale porous media thermal conductivity.Macroscale porous media thermal conductivity models were then revised for nanoporous media.The effective thermal conductivities of two packed beds with nanoscale nickel particles and a packed bed with microscale nickel particles were then measured using the Hot Disk.The measured results show that the nano/microscale porous media thermal conductivities were much less than the thermal conductivities of the solid particles.Comparison of the measured and calculated results shows that the revised combined parallel-series model and the revised Hsu-Cheng model can accurately predict the effective thermal conductivities of micro-and nanoparticle packed beds.展开更多
Si/Gesuperlattices are promising thermoelec- tric materials to convert thermal energy into electric power. The nanoscale thermal transport in Si/Gesuperlattices is investigated via molecular dynamics （MD） simulation...Si/Gesuperlattices are promising thermoelec- tric materials to convert thermal energy into electric power. The nanoscale thermal transport in Si/Gesuperlattices is investigated via molecular dynamics （MD） simulation in this short communication. The impact of Si and Ge interface on the cross-plane thermal conductivity reduction in the Si/Gesuperlattices is studied by designing cone- structured interface and aperiodicity between the Si and Ge layers. The temperature difference between the left and right sides of the Si/Gesuperlattices is set up for none- quilibrium MD simulation. The spatial distribution of temperature is recorded to examine whether the steady- state has been reached. As a crucial factor to quantify thermal transport, the temporal evolution of heat flux flowing through Si/Gesuperlattices is calculated. Com- pared with the even interface, the cone-structured interface contributes remarkable resistance to the thermal transport, whereas the aperiodic arrangement of Si and Ge layers with unequal thicknesses has a marginal influence on the reduction of effective thermal conductivity. The interface with divergent cone-structure shows the most excellent performance of all the simulated cases, which brings a 33% reduction of the average thermal conductivity to the other Si/Gesuperlattices with even, convergent cone-structured interfaces and aperiodic arrangements. The design of divergent cone-structured interface sheds promising lighton enhancing the thermoelectric efficiency of Si/Ge based materials.展开更多
Engineering in vacuum or under a protective atmosphere permits the production of materials, wherever the absence of oxygen is an essential demand for a successful processing. However, very few studies have provided qu...Engineering in vacuum or under a protective atmosphere permits the production of materials, wherever the absence of oxygen is an essential demand for a successful processing. However, very few studies have provided quantitative evidence of the effect of oxidized surfaces to tribological properties. In the current study on 99.99% pure copper, it is revealed that tribo-oxidation and the resulting increased abrasive wear can be suppressed by processing in an extreme high vacuum (XHV) adequate environment. The XHV adequate atmosphere was realized by using a silane-doped shielding gas (1.5 vol% SiH4 in argon). To analyse the influence of the ambient atmosphere on the tribological and mechanical properties, a ball–disk tribometer and a nanoindenter were used in air, argon, and silane-doped argon atmosphere for temperatures up to 800 ℃. Resistance measurements of the resulting coatings were carried out. To characterize the microstructures and the chemical compositions of the samples, the scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used. The investigations have revealed a formation of η-Cu3Si in silane-doped atmosphere at 300 ℃, as well as various intermediate stages of copper silicides. At temperatures above 300 ℃, the formation of γ-Cu5Si were detected. The formation was linked to an increase in hardness from 1.95 to 5.44 GPa, while the Young’s modulus increased by 46% to 178 GPa, with the significant reduction of the wear volume by a factor of 4.5 and the suppression of further oxidation and susceptibility of chemical wear. In addition, the relevant diffusion processes were identified using molecular dynamics (MD) simulations.展开更多
文摘Molecular Dynamics (MD) simulations of siliceous FAU-type zeolite were carried out at various temperatures. to investigate its thermal behaviors. From the study. we found that pure silicon fanjasite showed different thermal behaviors below 1500K and above 1500K. its cell volume gradually shrinks with the rising of the temperature below 1500K. the cell volume of the zeolite changes little above 1500K.
基金the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(No.51621004)the National Natural Science Foundation of China(Nos.12072109,51871092,and 11772122)。
文摘High entropy alloys(HEAs)attract remarkable attention due to the excellent mechanical performance.However,the origins of their high strength and toughness compared with those of the traditional alloys are still hardly revealed.Here,using a microstructure-based constitutive model and molecular dynamics(MD)simulation,we investigate the unique mechanical behavior and microstructure evolution of FeCoCrNiCu HEAs during the indentation.Due to the interaction between the dislocation and solution,the high dislocation density in FeCoCrNiCu leads to strong work hardening.Plentiful slip systems are stimulated,leading to the good plasticity of FeCoCrNiCu.The plastic deformation of FeCoCrNiCu is basically affected by the motion of dislocation loops.The prismatic dislocation loops inside FeCoCrNiCu are formed by the dislocations with the Burgers vectors of a/6[112]and a/6[112],which interact with each other,and then emit along the<111>slip direction.In addition,the mechanical properties of FeCoCrNiCu HEA can be predicted by constructing the microstructure-based constitutive model,which is identified according to the evolution of the dislocation density and the stress-strain curve.Strong dislocation strengthening and remarkable lattice distortion strengthening occur in the deformation process of FeCoCrNiCu,and improve the strength.Therefore,the origins of high strength and high toughness in FeCoCrNiCu HEAs come from lattice distortion strengthening and the more activable slip systems compared with Cu.These results accelerate the discovery of HEAs with excellent mechanical properties,and provide a valuable reference for the industrial application of HEAs.
基金supported by the National Natural Science Foundation of China(Grant Nos.11975088 and 11705041)the Natural Science Foundation of Zhejiang Province,China(Grant No.LY15A050001)。
文摘Evolution of the charged grains in a two-dimensional dusty plasma under a spatially harmonic external force,in particular,their long-time behaviors after the force has been withdrawn,is studied by using molecular dynamics simulation.Under an external force and a grain–grain interaction force,initially homogeneously distributed grains can reach a quasistationary state in the form of a disk crystal.After the external force is withdrawn,the disk moves initially with its size and shape nearly unchanged until it rapidly stops moving,and eventually the disk grain rotates like a vortex.The time needed to reach the final state increases with the strength of the initial external force increasing.
基金supported by the key project fund from the National Natural Science Foundation of China (Grant No. 50736003)the National Natural Science Foundation of China (Grant No. 50676047)
文摘The nanoparticle thermal conductivity and nanoscale thermal contact resistance were investigated by molecular dynamics(MD) simulations to further understand nanoscale porous media thermal conductivity.Macroscale porous media thermal conductivity models were then revised for nanoporous media.The effective thermal conductivities of two packed beds with nanoscale nickel particles and a packed bed with microscale nickel particles were then measured using the Hot Disk.The measured results show that the nano/microscale porous media thermal conductivities were much less than the thermal conductivities of the solid particles.Comparison of the measured and calculated results shows that the revised combined parallel-series model and the revised Hsu-Cheng model can accurately predict the effective thermal conductivities of micro-and nanoparticle packed beds.
文摘Si/Gesuperlattices are promising thermoelec- tric materials to convert thermal energy into electric power. The nanoscale thermal transport in Si/Gesuperlattices is investigated via molecular dynamics （MD） simulation in this short communication. The impact of Si and Ge interface on the cross-plane thermal conductivity reduction in the Si/Gesuperlattices is studied by designing cone- structured interface and aperiodicity between the Si and Ge layers. The temperature difference between the left and right sides of the Si/Gesuperlattices is set up for none- quilibrium MD simulation. The spatial distribution of temperature is recorded to examine whether the steady- state has been reached. As a crucial factor to quantify thermal transport, the temporal evolution of heat flux flowing through Si/Gesuperlattices is calculated. Com- pared with the even interface, the cone-structured interface contributes remarkable resistance to the thermal transport, whereas the aperiodic arrangement of Si and Ge layers with unequal thicknesses has a marginal influence on the reduction of effective thermal conductivity. The interface with divergent cone-structure shows the most excellent performance of all the simulated cases, which brings a 33% reduction of the average thermal conductivity to the other Si/Gesuperlattices with even, convergent cone-structured interfaces and aperiodic arrangements. The design of divergent cone-structured interface sheds promising lighton enhancing the thermoelectric efficiency of Si/Ge based materials.
基金The project was funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)(No.394563137-SFB 1368).
文摘Engineering in vacuum or under a protective atmosphere permits the production of materials, wherever the absence of oxygen is an essential demand for a successful processing. However, very few studies have provided quantitative evidence of the effect of oxidized surfaces to tribological properties. In the current study on 99.99% pure copper, it is revealed that tribo-oxidation and the resulting increased abrasive wear can be suppressed by processing in an extreme high vacuum (XHV) adequate environment. The XHV adequate atmosphere was realized by using a silane-doped shielding gas (1.5 vol% SiH4 in argon). To analyse the influence of the ambient atmosphere on the tribological and mechanical properties, a ball–disk tribometer and a nanoindenter were used in air, argon, and silane-doped argon atmosphere for temperatures up to 800 ℃. Resistance measurements of the resulting coatings were carried out. To characterize the microstructures and the chemical compositions of the samples, the scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used. The investigations have revealed a formation of η-Cu3Si in silane-doped atmosphere at 300 ℃, as well as various intermediate stages of copper silicides. At temperatures above 300 ℃, the formation of γ-Cu5Si were detected. The formation was linked to an increase in hardness from 1.95 to 5.44 GPa, while the Young’s modulus increased by 46% to 178 GPa, with the significant reduction of the wear volume by a factor of 4.5 and the suppression of further oxidation and susceptibility of chemical wear. In addition, the relevant diffusion processes were identified using molecular dynamics (MD) simulations.
