Atomic Simulation Study Of The Effects Of Vacancies On Plasticity And Phase Transformation Of Single-crystal Iron Under Shock Loading

Iron is an important component inside the earth,which is a high-pressure environment,so the study of physical properties of iron under high-pressure conditions is of great significance to the earth science and geological science.In addition,iron metal and its alloys are widely used in modern national defense,industrial production and other fields,and these fields are often encountered with high pressure conditions,so the study of high pressure response of iron can provide theoretical guidance in the research and development,manufacturing and application practice of iron-related products for the purpose of creating excellent products in the real world.There are a variety of defects(vacancy,dislocation,grain boundary,pore etc.)that inevitably exist in materials,which profoundly affect the properties of materials.In our work,the effects of vacancy defect on the plastic deformation and martensitic transformation of single-crystal iron under shock loading were investigated using non-equilibrium molecular dynamics simulations.The research outcomes are summarized as follows:(1)The macroscopic phenomena of shock plasticity and shock phase transformation induced by vacancy defect in three shock loading directions were discussed.Unique multiwave structures and reflection wave phenomenon were observed in our result.The existence of vacancies could reduce the Hugoniot elastic limit and pressure threshold of phase transformation,in addition,the vacancies could also reduce the propagation velocity of shock wave in the sample.In the[001]shock loading direction,atoms in HCP phase nucleated at the vacancy region,and no plasticity occurred before the phase transformation.In the[110]shock loading direction,obvious dislocation slip was observed,and the dislocations were emitted from the vacancy region,and the slip systems are identified as(112)[11(?)]and(11(?))[111].In the[111]shock loading direction,dislocation slip phenomenon,which was not found in the perfect single crystal model,appeared.The existence of vacancies has a great influence on the shock response of single-crystal iron.(2)The micromechanism of the vacancy-induced plastic deformation along the[110][111]shock loading direction was analyzed and discussed.The plastic deformation of the material was realized through the nucleation,growth and propagation of dislocation loops in the vacancy region.The vacancy interacted with each other under the influence of shock loading to form the vacancy cluster defect microstructures of different shapes with the evolution of time,and these generated vacancy cluster defect microstructures eventually collapsed from its center to form the dislocation loops with elliptical shape,which was distributed on the(112)or(11(?))plane and moved along[11(?)]or[111]crystal direction.Martensitic transformation is a two-step process which the atoms are first compressed along the[001]crystal direction and then shuffling between {110} crystal planes to form martensite with HCP structure.(3)In each shock loading direction,the samples with different vacancy concentrations were shocked in our simulations.It was found that for a specific shock loading velocity,there was a specific critical vacancy concentration in each shock loading direction.The increase in vacancy concentration had different effects on shock plasticity and shock phase transformation in different vacancy concentration ranges.When the vacancy concentration increased to a certain extent,the effect of the increase in vacancy concentration on the shock plasticity and shock phase transformation of single crystal iron became stabilized.