Simulation Study On Mechanical Behavior And Deformation Mechanism Of Nano-iron Metal

As a common method for simulating the performance of materials,molecular dynamics is characterized by the ability to trace the trajectories of atoms and analyze and predict the macroscopic properties of materials from the microscopic atomic level,thus providing a theoretical basis for the design of new materials.In this paper,a series of bi-crystal ?-irons with <110> and <100> as the rotating axes were selected as the research objects.The mechanics of hydrogen atoms on ?-iron under uniaxial tensile loading was studied by molecular dynamics simulation.The influence of performance,and the change process of the microstructure of the twin crystal ?-iron during the stretching process was analyzed by the ovito software.The main research contents and results are as follows:(1)The mechanical properties of ?3 bi-crystal ?-iron at different rotation angles were studied.The results show that the elastic stiffness,peak stress and peak strain of the bi-crystal ?-iron decrease with the increase of the rotation angle ? when the rotation angle is ?<45°.In the tensile loading,the original grain boundary of ?3 is deflected,and the deformation twin boundary is generated from the grain boundary.As the strain is further loaded,the pitch of the twin boundaries increases.The elastic stiffness of the four models with the rotation angle ?>45° is almost the same,but the peak stress and the peak strain do not seem to be regular with the change of the rotation angle.The three models of ?>64.76° undergo the process of decrystallization during the stretching process.(2)The effect of hydrogen atoms on the mechanical properties of ?3 bi-crystal ?-iron was investigated.In general,the peak stress of the bi-crystal ?-iron decreases as the hydrogen concentration increases.For ATGB samples with a hydrogen concentration greater than 1.5%,the curve is no longer similar to a small hydrogen concentration sample when peak stress is reached,but a rapid drop in stress occurs immediately.Hydrogen atoms hinder the growth of twins at the grain boundaries,and holes are first formed at the grain boundaries.As the stress continues to load,the holes further expand and form cracks toward the edges of the model.(3)The mechanical properties of ?5 bi-crystal ?-iron at different rotation angles were studied.The results show that the plastic deformation of bi-crystal ?-iron mainly proceeds through the transition of BCC phase to FCC phase and then to BCC phase.Due to the different Schmid factors on both sides of the grain boundary,the phase transition zone of the plastic phase exhibits an asymmetrical character.(4)The effect of hydrogen atoms on the mechanical properties of ?5 bi-crystal ?-iron was investigated.The results show that the addition of hydrogen atoms does not change the deformation mechanism of the crystal.As the hydrogen concentration increases,the interstitial hydrogen atoms weaken the bonding force between the iron atoms,resulting in a decrease in the peak stress of the twin crystal ?-iron.The addition of a hydrogen atom located in the BCC lattice octahedral gap reduces the bonding force between the iron atoms,thereby making the transition of the BCC phase to the FCC phase more likely to occur.The hydrogen atoms in the metastable FCC phase are located at the edge of the new BCC lattice,which also effectively hinders the transition of the FCC phase to the BCC phase.