The roles of crystallographic orientation, high-angle grain boundary, and indenter diameter during nano-indentation

Abstract

Molecular dynamics simulation of nano-indentation of single-crystal and bicrystal FCC aluminum is performed. The role of crystallographic orientation during nano-indentation of single-crystal aluminum is assessed. Then, the influence of the presence of a grain boundary is analyzed by adding high-angle symmetric tilt boundaries of 5<210>/(100) and 5<310>/(100) parallel to the surface on which the indentation is performed. Furthermore, in both cases, the size of the indenter is changed to investigate how the surface curvature of the indenter affects the nano-indentation process. The results suggest that in each crystallographic orientation, the presence of a grain boundary increases the required force for indentation, while the distance of a grain boundary from the indentation surface could affect the increase in the required force. Simulations prove that the grain boundary acts as a source of generation and emission of dislocations and restricts the penetration of the indenter by limiting the slip band formation and plastic deformation. The dislocation emission from the grain boundary restricts the penetration of the indenter and limits the formation of the octahedral slip systems of type {111}<110> and consequently increases the required force for indentation in bicrystals.