Activating non-basal<c+a>slip is a key method to improve room temperature ductility and formability of Mg alloys.However,the detailed criterion for activation of the<c+a>slip in multicomponent Mg alloys,wh...Activating non-basal<c+a>slip is a key method to improve room temperature ductility and formability of Mg alloys.However,the detailed criterion for activation of the<c+a>slip in multicomponent Mg alloys,which can be utilized in commercial Mg alloys,requires further understanding.The present authors investigated the mechanism and criterion using a molecular statics simulation on dislocation behaviors in multicomponent Mg alloys.We found that if multicomponent Mg alloys have an equivalent dislocation binding intensity to associated binary Mg alloys that are optimized to minimize the critical resolved shear stress anisotropy and thus activate the<c+a>slip,then the critical resolved shear stress anisotropy between slip systems of the multicomponent Mg alloys can also be minimized,resulting in activation of the<c+a>slip.The activation is maximized in multicomponent Mg alloys when alloying a large amount of weak dislocation binding elements.It was confirmed through experiments that the multicomponent Mg alloys satisfying the above criterion show higher room-temperature tensile elongation and formability than other alloys.展开更多
In this paper,a semi-analytical method was proposed to evaluate the acoustic nonlinearity parameter for single crystals of Cu,Ag and Au.The acoustic nonlinearity parameter can be derived analytically by general expres...In this paper,a semi-analytical method was proposed to evaluate the acoustic nonlinearity parameter for single crystals of Cu,Ag and Au.The acoustic nonlinearity parameter can be derived analytically by general expressions in terms of the interatomic potentials with the distances between each pair of atoms in these transition metals.To evaluate the acoustic nonlinearity parameter,one needs to conduct one step molecular static simulation and obtain the equilibrium positions of all the atoms.Further,based on this method,numerical experiments with molecular dynamic code LAMMPS were given to compute the acoustic nonlinearity parameter of Cu,Ag and Au.To illustrate the validity of these expressions,comparison was made between calculation results and data in the literature.Reasonable agreement is observed.Because of the analytical nature of this method,it provides a fundamental understanding of the nonlinear elastic behavior of these transition metals.展开更多
Nanoindentation is a useful technique to measure material properties at microscopic level.However,the intrinsically multiscale nature makes it challenging for large-scale simulations to be carried out.It is shown that...Nanoindentation is a useful technique to measure material properties at microscopic level.However,the intrinsically multiscale nature makes it challenging for large-scale simulations to be carried out.It is shown that in molecular statics simulations of nanoindentation,the separated dislocation loops(SDLs)are trapped in simulation box which detrimentally affects the plastic behavior in the plastic zone(PZ);and the long-distance propagation of SDLs consumes much computational cost yet with little contribution to the variation of tip force.To tackle the problem,the dislocation loop erasing(DLE)method is proposed in the work to alleviate the influence of artificial boundary conditions on the SDL–PZ interaction and improve simulation efficiency.Simulation results indicate that the force–depth curves obtained from simulations with and without DLE are consistent with each other,while the method with DLE yields more reasonable results of microstructural evolution and shows better efficiency.The new method provides an alternative approach for large-scale molecular simulation of nanoindentation with reliable results and higher efficiency and also sheds lights on improving existing multiscale methods.展开更多
Twin formation energy is an intrinsic quantity for bulk crystals.At the nanoscale,the twin formation energy of covalent SiC nanowires goes up with decreasing dimension.In contrast,this article reports that the twin fo...Twin formation energy is an intrinsic quantity for bulk crystals.At the nanoscale,the twin formation energy of covalent SiC nanowires goes up with decreasing dimension.In contrast,this article reports that the twin formation energy of metallic nanowires goes down with decreasing dimension.This result is based on classical molecular statics simulations of four representative metals.Cu and Al represent face-centered cubic(FCC)metals of low and high twin formation energies.Ta represents a body-centered cubic(BCC)metal,and Mg represents a hexagonal close-packed(HCP)metal.For all the four metals,the dependence of twin formation energy on size correlates with lower twin formation energy near surfaces,according to atomic-level analysis.Based on this atomic-level insight,the authors propose a core–shell model that reveals the twin formation energy as inversely proportional to the diameter of nanowires.This dependence is in agreement with the results of molecular statics simulations.展开更多
基金the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Science&ICT(2016R1A2B4006680).
文摘Activating non-basal<c+a>slip is a key method to improve room temperature ductility and formability of Mg alloys.However,the detailed criterion for activation of the<c+a>slip in multicomponent Mg alloys,which can be utilized in commercial Mg alloys,requires further understanding.The present authors investigated the mechanism and criterion using a molecular statics simulation on dislocation behaviors in multicomponent Mg alloys.We found that if multicomponent Mg alloys have an equivalent dislocation binding intensity to associated binary Mg alloys that are optimized to minimize the critical resolved shear stress anisotropy and thus activate the<c+a>slip,then the critical resolved shear stress anisotropy between slip systems of the multicomponent Mg alloys can also be minimized,resulting in activation of the<c+a>slip.The activation is maximized in multicomponent Mg alloys when alloying a large amount of weak dislocation binding elements.It was confirmed through experiments that the multicomponent Mg alloys satisfying the above criterion show higher room-temperature tensile elongation and formability than other alloys.
基金financially supported by the National Sci-Tech Support Plan(No.2015BAF06B01)。
文摘In this paper,a semi-analytical method was proposed to evaluate the acoustic nonlinearity parameter for single crystals of Cu,Ag and Au.The acoustic nonlinearity parameter can be derived analytically by general expressions in terms of the interatomic potentials with the distances between each pair of atoms in these transition metals.To evaluate the acoustic nonlinearity parameter,one needs to conduct one step molecular static simulation and obtain the equilibrium positions of all the atoms.Further,based on this method,numerical experiments with molecular dynamic code LAMMPS were given to compute the acoustic nonlinearity parameter of Cu,Ag and Au.To illustrate the validity of these expressions,comparison was made between calculation results and data in the literature.Reasonable agreement is observed.Because of the analytical nature of this method,it provides a fundamental understanding of the nonlinear elastic behavior of these transition metals.
基金Supports from the National Natural Science Foundation of China(Grant Nos.11790292,11672298,and 11432014)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(XDB22040501)are gratefully acknowledged.Computations are performed on the ScGrid of Supercomputing Center,Computer Network Information Center of Chinese Academy of Sciences and LNMGrid of the State Key Laboratory of Nonlinear Mechanics.
文摘Nanoindentation is a useful technique to measure material properties at microscopic level.However,the intrinsically multiscale nature makes it challenging for large-scale simulations to be carried out.It is shown that in molecular statics simulations of nanoindentation,the separated dislocation loops(SDLs)are trapped in simulation box which detrimentally affects the plastic behavior in the plastic zone(PZ);and the long-distance propagation of SDLs consumes much computational cost yet with little contribution to the variation of tip force.To tackle the problem,the dislocation loop erasing(DLE)method is proposed in the work to alleviate the influence of artificial boundary conditions on the SDL–PZ interaction and improve simulation efficiency.Simulation results indicate that the force–depth curves obtained from simulations with and without DLE are consistent with each other,while the method with DLE yields more reasonable results of microstructural evolution and shows better efficiency.The new method provides an alternative approach for large-scale molecular simulation of nanoindentation with reliable results and higher efficiency and also sheds lights on improving existing multiscale methods.
基金The authors acknowledge the financial support of Defense Threat Reduction Agency(HDTRA1-09-1-0027)H.H.also acknowledges the financial support of National Science Foundation(DMR0906349 and CMMI-0856426).
文摘Twin formation energy is an intrinsic quantity for bulk crystals.At the nanoscale,the twin formation energy of covalent SiC nanowires goes up with decreasing dimension.In contrast,this article reports that the twin formation energy of metallic nanowires goes down with decreasing dimension.This result is based on classical molecular statics simulations of four representative metals.Cu and Al represent face-centered cubic(FCC)metals of low and high twin formation energies.Ta represents a body-centered cubic(BCC)metal,and Mg represents a hexagonal close-packed(HCP)metal.For all the four metals,the dependence of twin formation energy on size correlates with lower twin formation energy near surfaces,according to atomic-level analysis.Based on this atomic-level insight,the authors propose a core–shell model that reveals the twin formation energy as inversely proportional to the diameter of nanowires.This dependence is in agreement with the results of molecular statics simulations.