Analysis of dislocation mechanisms around indentations through slip step observations

Atomic force microscopy has been used to study slip step patterns, which form around indentations in FCC alloys. These patterns form in a consistent and repeatable manner. From these observations it has been determined that slip steps increase in height only in the outer region of the plastic zone leading to the cessation of their growth as the plastic zone expands outward. Electron backscatter diffraction techniques are used to map grain orientation and the effect of different surface orientations as well as different tip geometries on slip step behavior is explored. Changes in resolved shear stress on different slip planes can be observed qualitatively from changes in the slip step patterns as surface orientation and tip geometry are varied. Pile up is shown to form above the regions with the largest amounts of strain downward into the bulk. Changes in slip step patterns can be predicted based on changes in resolved shear stress. Discreet dislocation dynamics simulations have been performed to support these observations.