Dynamic Structural Evolution of Nanocrystalline Aluminum During Ratcheting Deformation

The ratcheting deformation mechanism and dislocation behavior at the grain boundary (GB) of nanocrystalline (NC) aluminum (Al) with a grain size of ∼8 nm are investigated by molecular dynamics simulations at various temperatures (i.e., 77 K, 300 K, and 560 K). The structural evolution and dislocation nature are studied at the atomic level during ratcheting deformation. This study reveals that dislocation–dislocation interactions cause stacking faults and twin boundary formation in NC Al specimens subjected to low-cycle fatigue loading conditions. Ratcheting strain accumulation augments as the NC Al specimen undergoes more ratcheting deformation cycles. The dislocation density is observed to be comparatively high if the deformation occurs at cryogenic temperature. The dislocation mobility, dislocation loop formations, and dislocation entanglements are observed during the ratcheting process. The total Shockley partial dislocation cumulative length is increased as the ratcheting deformation progresses. Shockley partial and perfect dislocations are the significant contributors to the ratcheting deformation process in the case of ultrafine grain NC Al. Correspondingly, the post-processing analysis work of ratcheting deformation behavior is performed with the common neighbor analysis, atomic strain, dislocation analysis, Wigner–Seitz defect analysis, and centrosymmetry parameter tools of the OVITO software.