Atomistic simulations of the surface severe plastic deformation-induced grain refinement in polycrystalline magnesium : the effect of processing parameters

Abstract

Magnesium (Mg) based alloys are promising candidates for many applications, but their untreated surfaces usually have low strength and hardness. In this study, a single point diamond turning (SPDT) technique was applied to refine the grain size and improve the mechanical properties of the surface layers of Mg-Li alloys. By refining grains in the topmost layer to the nanometer scale (∼ 60 nm), the surface hardness was found to be enhanced by approximately 60%. The atomic plastic deformation process during the SPDT was then studied by the real-time atomistic molecular dynamics (MD) simulations. A series of MD simulations with different combinations of parameters, including rake angle, cutting speed and cutting depth, were conducted to understand their influences on the microstructural evolution and associated plastic deformation mechanisms on the surface layer of the workpieces. The MD simulation results suggest that using increased rake angle, cutting speed and cutting depth can help to achieve better grain refinement. These simulation results, which provide atomic-level details of the deformation mechanism, can assist the parameter design for the SPDT techniques to achieve the high-performance heterogeneous nanostructured materials.