An Atomistic Study On Shock-compression Response In Iron-based Single Crystal Iron With Dislocations

The study of physical properties of solid materials under high pressure conditions is of great significance to basic theory,industrial production and state defense engineering.Iron is the main element of earth's core,which widely exits in nature and has important application in industrial and military fields.Researchers and industrialists are particularly interested in the properties of iron under high pressure conditions.In engineering applications,various types of defects inevitably exist in materials which would critically affect their properties.Effects of defects on shock response attract much attention in recent years.In this work,the non-equilibrium molecular dynamics method is adopted to simulate the shock-compression response of iron-based single crystal with multiple dislocation structures,and the research mainly includes the following three parts:(1)An edge dislocation structure is constructed in the iron-based single crystal model and then subjects to shock loading.The initial edge dislocation can be the nucleation site contributes to the multiplication of new-generated dislocations as shown in the simulation results.An self-adaptive transition of the activated slip systems has been observed,from {110}<111> to {112}<111>,because of the influences of initial edge dislocation structure and Schmidt factor.The shear stress along shuffle plane gradually increases with the help of plastic slip before phase transition,so the HCP phase concentrates in the area which accompanies dramatical plastic deformation.(2)We construct a single crystal iron model with interstitial dislocation loop and simulate the shock process as well.Under shock loading along [001] direction,the habit plane of dislocation loop continuously changes and finally stabilizes on(111)plane.The(111)plane is not the typical slip plane with respect to BCC structure,so the dislocation loop has been “constrained” which leads to the restraint in plasticity.The dislocation loop can be the nucleation site for phase transition under higher shock strength.We have observed the phenomenon that HCP phases preferentially grow around the initial dislocation loop.The dislocation loop outward extends on(112)plane when shock loading along [110] direction.Jogs and kinks are produced in the extension process,which can launch more new-generated dislocations under high-strength shock condition.This behavior makes great contribution to plasticity.(3)Both of the edge dislocation and dislocation loop are built in a single model to investigate the intersection of dislocation under shock loading.Based on the results of DXA method,the intersection process is completed through synthetic and decomposition reactions of dislocations.Two kinds of dislocation are tangled and developed to a three-dimensional network after intersection.Phase transition preferentially takes place at the tangled area,which means intensive deformation is beneficial to the occurrence of phase transition.