Molecular dynamics study on grain refinement process of α-iron by equal channel angular pressing under quasi 3-dimensional condition

Abstract

Equal Channel Angular Pressing (ECAP) has potentiality for producing ultrafine-grained polycrystalline metals in bulk with very high yield stress and excellent workability, under an optimized processing condition. In this study, molecular dynamics (MD) simulations were performed in order to reveal the dependence of metallographic structure evolution on the processing route, and also to clarify the grain refinement mechanism in α-iron by ECAP with a 90° die. We used Lees-Edwards periodic boundary condition to impose a severe plastic deformation which is ideally equivalent to the simple shear deformation produced at the intersecting plane of two channels. The transition of the internal structure during 4 passes were investigated for the feasible four kinds of processing route under quasi 3-dimensional condition. It is shown that the twinning deformation is dominant for the analyzed material, and the texture evolution is notably affected by the relationship between applied simple shear direction and the characteristic crystal orientation which can easily cause twinning deformation. The simplest processing route with no rotation of billet between passes, which is called Route A in general, is the most efficient route in the presently analyzed cases. This is because the twinning deformation along the simple shear direction intersects with the twin boundaries which are developed by stress component conjugate to the simple shear.