Nanoindentation behavior of nanotwinned Cu: Influence of indenter angle on hardness, strain rate sensitivity and activation volume

The influence of strain on the mechanical properties and deformation kinetic parameters of nanotwinned (nt) copper is investigated by a series of nanoindentation experiments, which were performed by employing sharp indenters with five varying centerline-to-face angles (ψ). Comparison experiments were also conducted on (1 1 0) single crystalline Cu. Experimental results indicate that, unlike coarse-grained materials, nt-Cu is prone to plastic flow softening with large material pile-up around the indentation impression at high levels of strains. Localized detwinning becomes more significant with decreasing ψ, concomitant with reduced strain-rate sensitivity (m) and enhanced activation volume (V*). The m of nt-Cu is found to depend sensitively on ψ with a variation of more than a factor of 3, whereas V* exhibits a much less sensitive trend. This paper discusses the validation of the experimental techniques and the implications of various deformation kinetic parameters on the underlying deformation mechanisms of nt-Cu.