Atomic insight of deformation mechanism of monocrystalline pure iron upon equal channel angular pressing: Molecular dynamics simulation

Equal channel angular pressing (ECAP) is a widely used severe plastic deformation technique for producing ultrafine-grained metals with enhanced mechanical properties. Despite substantial experimental efforts that have established the macroscopic effects of ECAP, the atomic-scale deformation mechanisms in body-centered cubic (BCC) pure iron are still not fully understood. In particular, the role of initial crystallographic orientation in governing the competition between simple shear and compressive deformation during ECAP remains unresolved at the atomistic level. In this study, three monocrystalline pure iron samples with different initial orientations were examined using molecular dynamics simulations: a 100-sample with the [100] direction aligned parallel to the extrusion direction (ED), a 111-sample with the [111] direction aligned parallel to the ED, and an R45-sample with the [111] direction oriented at 45° to the ED. The deformation behavior was analyzed in terms of simple shear and compression mechanisms. The results reveal strong orientation dependence. The 100-sample predominantly deformed by simple shear throughout the extrusion process, consistent with shear factor predictions. In contrast, the 111-sample, characterized by fewer active slip systems, was mainly governed by compression, with simple shear occurring only at later stages. The R45-sample exhibited a mixed deformation behavior combining features of both orientations. All samples showed grain fragmentation and polycrystallization, while twin formation was observed in the 100-sample due to simple shear. These findings highlight the critical role of crystallographic orientation in ECAP deformation behavior and provide atomistic insights to support process optimization.