Molecular Dynamics Simulation Of The Plastic Deformation Mechanism For Magnesium Bi-crystals

Due to the excellent properties such as low density,high strength,superior damping capacity,and efficient recyclability.magnesium and magnesium alloys have have been widely used in transportation,medical,aerospace,national defense and other fields.In general,the mechanical properties of materials were closely related to their microstructure and internal deformation mechanism.Recently,some research on the strengthening and toughening of nano-twin show that twin structure can be used to improve the strength and toughness of materials.Moreover,computational simulation techniques have been widely used to study the mechanical behavior and deformation mechanism of nano-scale materials.Molecular dynamics can reflect the evolution process of microstructures by tracking the microscopic motion details of atoms,and can be used to study the macroscopic mechanics of materials.It becomes an important bridge which connects the microscopic scale to the macroscopic scale.In this paper,molecular dynamics simulations were performed to study the uniaxial compression deformation of bi-crystal magnesium nanopillars with a {10(?)2} twin boundary(TB).In addition,temperature dependence on the plastic deformation behavior in magnesium bi-crystal were discussed in detail.The main research work and progress of this paper are as follows:1.Simulation results showed that the initial deformation mechanism was mainly caused by the migration of the TB,and the transformation of TB into(basal/prismatic)B/P interface was observed.After that,basal slip as well as pyramidal slip nucleated during the plastic deformation process.Moreover,a competition mechanism between twin boundary migration and basal slip was found.Basal slip can inhibit the migration of the twin boundary,and new {10(?)1} <10(?)2 > twins appear at a certain high strain level(ε=0.104).In addition,Schmid Factor(SF)analysis was conducted to understand the activations of deformation modes.2.Temperature dependence on the plastic deformation mechanism in magnesium bi-crystal nanopillars.(1)The critical nucleation stress of the TB migration decreases with the increase of temperature.It was because that atoms are more active at high temperatures,and it can obtain more energy to overcome the energy barrier.Therefore,the stress required for the TB migration is smaller.(2)During the plastic deformation stage,the activation of Shockley partial dislocations near the TB was also different at various temperature.By calculating the Stacking Fault Energy(SFE)of basal slip at various temperature,we obtain that: the Shockley partial dislocations are more likely to occur at low temperatures(T<200K).When the temperature was above 200 K,the plastic deformation was mainly dominated by full dislocations.In addition,through the microscopic deformation process,we found that the nucleation of partial dislocations gradually becomes difficult with the increase of temperature.No partial dislocation nucleation was observed near the TB when the temperature was above 200 K.(3)Temperature also has an effect on the nucleation of the new twin.New {10(?)1} <10(?)2 > twin was observed during the later plastic stage at 10K-200 K,while at 250K-500 K,a large number of basal dislocations were observed in the nanopillar,and they inhibit the nucleation of new twins.