Dislocation structure evolution pathway in surface and bulk regions of Ni deformed in tension: a comparison

The study examines the evolution of dislocation structures in pure nickel with specific orientations near [100], [110] and [111]. The dislocation evolution pathways of grains with different orientations in both surface and bulk regions have been systematically investigated. It was observed that the development of dislocation structures in surface and bulk grains is not synchronous. During the early stages of plastic deformation, dislocation self-organization in surface grains is promoted more than in the bulk. However, as the strain increases, the situation is reversed, and cell block formation is largely postponed in the surface region. At high strain levels, orientation dependence of dislocation structures in the Ni surface region basically follows the same rule as the bulk, while at low strain levels, it does not. The slip band emergence on the crystal surface does not necessarily correspond with the dislocation pattern beneath it. The minimum strain level of cell block formation for [110] corner is lower than that for [111] corner. These findings deepen our understanding on the deformation mechanism of FCC metals.