Mechanical properties of high-entropy alloys(HEAs)with the face-centered cubic(fcc)structure strongly depend on their initial grain orientations.However,the orientation-dependent mechanical responses and the underlyin...Mechanical properties of high-entropy alloys(HEAs)with the face-centered cubic(fcc)structure strongly depend on their initial grain orientations.However,the orientation-dependent mechanical responses and the underlying plastic fl ow mechanisms of such alloys are not yet well understood.Here,deformation of the equiatomic FeMnCoCrNi HEA with various initial orientations under uniaxial tensile testing has been studied by using atomistic simulations,showing the results consistent with the recent experiments on fcc HEAs.The quantitative analysis of the activated deformation modes shows that the initiation of stacking faults is the main plastic deformation mechanism for the crystals initially oriented with[001],[111],and[112],and the total dislocation densities in these crystals are higher than that with the[110]and[123]orientations.Stacking faults,twinning,and hcp-martensitic transformation jointly promote the plastic deformation of the[110]orientation,and twinning in this crystal is more significant than that with other orientations.Deformation in the crystal oriented with[123]is dominated by the hcp-martensite transformation.Comparison of the mechanical behaviors in the FeMnCoCrNi alloy and the conventional materials,i.e.Cu and Fe50Ni50,has shown that dislocation slip tends to be activated more readily in the HEA.This is attributed to the larger lattice distortion in the HEA than the low-entropy materials,leading to the lower critical stress for dislocation nucleation and elastic–plastic transition in the former.In addition,the FeMnCoCrNi HEA with the larger lattice distortion leads to an enhanced capacity of storing dislocations.However,for the[001]-oriented HEA in which dislocation slip and stacking fault are the dominant deformation mechanisms,the limited deformation modes activated are insu fficient to improve the work hardening ability of the material.展开更多
Molecular dynamics simulations are carried out in order to Study the atomic structure of crystalline component of nanocrystalline α-Fe when it is consolidated from small grains. A two-dimensional computational block ...Molecular dynamics simulations are carried out in order to Study the atomic structure of crystalline component of nanocrystalline α-Fe when it is consolidated from small grains. A two-dimensional computational block is used to simulate the consolidation process. All the preset dislocations in the original grains glide out of them in the consolidation process, but new dislocations can generate when the grain size is large enough. It shows that dislocations exist in the consolidated material rather than in the original grains. Whether dislocations exist in the crystalline component of the resultant model nano-material depends upon grain size. The critical value of grain size for dislocation generation appears to be about 9 nm. This result agrees with experiments qualitatively.展开更多
A computer program has been developed for the moIlcular dynamics calculation of ionic orstrong-ionic covalent systems. Ewald summation algorithm and Keating potentiaI model areadopted to calculate the long-range Coulo...A computer program has been developed for the moIlcular dynamics calculation of ionic orstrong-ionic covalent systems. Ewald summation algorithm and Keating potentiaI model areadopted to calculate the long-range Coulomb interaction and the short-range bonding forces,respectively. A theoretical study on the domain boundary structures in epitaxial wurtzite GaN film is accomplished with the program. The calculation result is used in the structure formationexplanation of an interesting defect observed by HREM experiment.展开更多
Molecular dynamics simulations are performed to study the nanoindentation models of monolayer suspended graphene and graphyne. Fullerenes are selected as indenters. Our results show that Young＇s modulus of monolayer-...Molecular dynamics simulations are performed to study the nanoindentation models of monolayer suspended graphene and graphyne. Fullerenes are selected as indenters. Our results show that Young＇s modulus of monolayer-thick graphyne is almost half of that of graphene, which is estimated to be 0.50 TPa. The mechanical properties of graphene and graphyne are different in the presence of strain. A pre-tension has an important effect on the mechanical properties of a membrane. Both the pre-tension and Young＇s modulus plots demonstrate index behavior. The toughness of graphyne is stronger than that of graphene due to Young＇s modulus magnitude. Young＇s moduli of graphene and graphyne are almost independent of the size ratio of indenter to membrane.展开更多
Heat conduction of nanoconfined liquid may differ from its bulk because of the effects of size,geometry,interface,temperature,etc.In this study,the roles of some critical factors for the heat conduction of nanoconfine...Heat conduction of nanoconfined liquid may differ from its bulk because of the effects of size,geometry,interface,temperature,etc.In this study,the roles of some critical factors for the heat conduction of nanoconfined water film are systematically analyzed by using the molecular dynamics method.With decreasing thickness,the normal thermal conductivity of nanoconfined water film between two copper plates decreases exponentially,while the thermal resistance,peak of the radial distribution function,and atomistic heat path increase exponentially.The average bond order,radial distribution function,mean squared displacement,and vibrational density of states are calculated to analyze the effects of structure,distribution,molecular diffusion,and vibration of water molecules on heat conduction especially in a region having no oxygen atoms(which is observed by the near-wall density profile).The results show that phonon scattering is dominant for determining the reduced thermal conductivity in this near-wall region.The thermal conductivity ratio of confined water film to bulk water has a roughly linear relationship with the logarithm of the proportion of the near-wall region.Moreover,the high interfacial thermal resistance is positively correlated to the film thickness,but it has a negligible impact on heat conduction.This work provides insights into the contribution of water molecules near the solid/liquid interface to the heat conduction of nanoconfined liquid for process intensification.展开更多
基金financially supported by the National Natural Science Foundation of China(No.51922026)the Fundamental Research Funds for the Central Universities(Nos.N2002005 and N2007011)+1 种基金the Liaoning Natural Science Foundation(No.20180510010)the 111 Project(No.B20029)。
文摘Mechanical properties of high-entropy alloys(HEAs)with the face-centered cubic(fcc)structure strongly depend on their initial grain orientations.However,the orientation-dependent mechanical responses and the underlying plastic fl ow mechanisms of such alloys are not yet well understood.Here,deformation of the equiatomic FeMnCoCrNi HEA with various initial orientations under uniaxial tensile testing has been studied by using atomistic simulations,showing the results consistent with the recent experiments on fcc HEAs.The quantitative analysis of the activated deformation modes shows that the initiation of stacking faults is the main plastic deformation mechanism for the crystals initially oriented with[001],[111],and[112],and the total dislocation densities in these crystals are higher than that with the[110]and[123]orientations.Stacking faults,twinning,and hcp-martensitic transformation jointly promote the plastic deformation of the[110]orientation,and twinning in this crystal is more significant than that with other orientations.Deformation in the crystal oriented with[123]is dominated by the hcp-martensite transformation.Comparison of the mechanical behaviors in the FeMnCoCrNi alloy and the conventional materials,i.e.Cu and Fe50Ni50,has shown that dislocation slip tends to be activated more readily in the HEA.This is attributed to the larger lattice distortion in the HEA than the low-entropy materials,leading to the lower critical stress for dislocation nucleation and elastic–plastic transition in the former.In addition,the FeMnCoCrNi HEA with the larger lattice distortion leads to an enhanced capacity of storing dislocations.However,for the[001]-oriented HEA in which dislocation slip and stacking fault are the dominant deformation mechanisms,the limited deformation modes activated are insu fficient to improve the work hardening ability of the material.
文摘Molecular dynamics simulations are carried out in order to Study the atomic structure of crystalline component of nanocrystalline α-Fe when it is consolidated from small grains. A two-dimensional computational block is used to simulate the consolidation process. All the preset dislocations in the original grains glide out of them in the consolidation process, but new dislocations can generate when the grain size is large enough. It shows that dislocations exist in the consolidated material rather than in the original grains. Whether dislocations exist in the crystalline component of the resultant model nano-material depends upon grain size. The critical value of grain size for dislocation generation appears to be about 9 nm. This result agrees with experiments qualitatively.
文摘A computer program has been developed for the moIlcular dynamics calculation of ionic orstrong-ionic covalent systems. Ewald summation algorithm and Keating potentiaI model areadopted to calculate the long-range Coulomb interaction and the short-range bonding forces,respectively. A theoretical study on the domain boundary structures in epitaxial wurtzite GaN film is accomplished with the program. The calculation result is used in the structure formationexplanation of an interesting defect observed by HREM experiment.
基金Supported by the National Natural Science Foundation of China under Grant No 11274262the Natural Science Foundation of Hunan Province under Grand No 14JJ2046the Program for Changjiang Scholars and Innovative Research Team in Universities under Grant No IRT13093
文摘Molecular dynamics simulations are performed to study the nanoindentation models of monolayer suspended graphene and graphyne. Fullerenes are selected as indenters. Our results show that Young＇s modulus of monolayer-thick graphyne is almost half of that of graphene, which is estimated to be 0.50 TPa. The mechanical properties of graphene and graphyne are different in the presence of strain. A pre-tension has an important effect on the mechanical properties of a membrane. Both the pre-tension and Young＇s modulus plots demonstrate index behavior. The toughness of graphyne is stronger than that of graphene due to Young＇s modulus magnitude. Young＇s moduli of graphene and graphyne are almost independent of the size ratio of indenter to membrane.
基金the National Natural Science Foundation of China(No.51876058)。
文摘Heat conduction of nanoconfined liquid may differ from its bulk because of the effects of size,geometry,interface,temperature,etc.In this study,the roles of some critical factors for the heat conduction of nanoconfined water film are systematically analyzed by using the molecular dynamics method.With decreasing thickness,the normal thermal conductivity of nanoconfined water film between two copper plates decreases exponentially,while the thermal resistance,peak of the radial distribution function,and atomistic heat path increase exponentially.The average bond order,radial distribution function,mean squared displacement,and vibrational density of states are calculated to analyze the effects of structure,distribution,molecular diffusion,and vibration of water molecules on heat conduction especially in a region having no oxygen atoms(which is observed by the near-wall density profile).The results show that phonon scattering is dominant for determining the reduced thermal conductivity in this near-wall region.The thermal conductivity ratio of confined water film to bulk water has a roughly linear relationship with the logarithm of the proportion of the near-wall region.Moreover,the high interfacial thermal resistance is positively correlated to the film thickness,but it has a negligible impact on heat conduction.This work provides insights into the contribution of water molecules near the solid/liquid interface to the heat conduction of nanoconfined liquid for process intensification.
