Anisotropic plastic deformation beneath surface step during nanoindentation of FCC Al by multiscale analysis

Anisotropic plastic deformation beneath surface step during nanoindentation process is investigated applying the quasicontinuum (QC) method. Microscopic mechanisms of effects of surface step on FCC Al ( 1 ¯ 1 0 ) , (1 1 1), and (0 0 1) planes under the action of a cylindrical indenter are systematically studied. For steps on ( 1 ¯ 1 0 ) plane, dislocations nucleation and emission beneath surface steps is the main plastic deformation characteristic; for steps on (1 1 1) plane, the crystal lattice beneath the step undergoes severe distortion and rotation; for steps on (0 0 1) plane, deformation twinning and dislocation lock can be observed beneath the surface step. Load–displacement responses of various orientations and roughness are discussed in detail. The concept of geometrically necessary displacement is proposed to describe step flattening process. Strain energy for nanoindentation on stepped and flat surfaces under various crystal orientations is analyzed and compared to further investigate the effect of crystal anisotropic plastic deformation. The description about the atomistic behavior beneath surface step and the discussion about the anisotropic plastic deformation of surface step are meaningful for understanding the influence of surface step on the nanoindentation tests.