The Development And Applications Of Meta-atom Molecular Dynamic Method

Alloys have attracted wide attentions in research because of their wide and lasting applications in industries. In simulation, massively parallel molecular dynamics (MD) simulations have been performed to understand the plastic deformation of metals. However, the intricate interplay between the deformation mechanisms and various material properties is largely unknown in metallic alloys due to the limited available interatomic potentials. Here we propose a meta-atom method for MD simulations of alloy systems based on the embedded atom method (EAM).The meta-atom MD simulation (MAMD) method is proposed based on two assumptions:Similarity principle and average principle. One set of computer program is developed based on these principles to produce the MAMD potentials. In this program, we propose the "geometric factor" and "white noise" methods to lower the time-cost of producing one potential.To testify our MAMD method, both meta-atom potentials for aluminum bronzes and hypothetic face-centered-cubic metals have been developed to study the parametric dependence of deformation mechanisms, which captures the essence of competitions between dislocation motion and twinning or cleavage. Moreover, the solid-solution strengthening effect can be simply accounted by introducing a scaling factor in the MAMD method. It is noted that the scaling factor is capable of introducing dispersively distributed lattice distortion to crystal. Although scaling factor has small influence on the material properties of alloys, the Peierls stress of dislocation is found increased proportional to the scaling factor.By this approach, massively parallel atomistic simulations on fully three-dimensional polycrystals have been performed to investigate deformation mechanisms of twinning-induced-plasticity (TWIP) steel. We have successfully reproduced the deformation behaviors of TWIP steel, captured the typical microstructures and revealed the dynamic interactions under deformation. The formation of deformation twinning refines the grains, blocks the dislocation and improve the capacity of dislocation in grains, indicating the enhancement of both ductility and strength of metals. Meanwhile, point vacancies and vacancy tubes are frequently observed in TWIP steel, which are produced by the nonconservative jog motion and stacking fault interactions.We expect that the calculation of macroscopic measurable quantities for engineering oriented alloys will become possible in this way, shedding light on understanding the material behavior and constructing materials with specific mechanical properties. This paves a way for understanding the mechanical behaviors of alloys by massively parallel MD simulations with increasing computational power.