Revealing the Maximum Strength in Nanotwinned Copper

TLDR

The strength of polycrystalline materials rises as grain size decreases, but below a critical size softening may occur, indicating the strongest size occurs at a transition from lattice dislocation to grain boundary mechanisms. The study investigated the maximum strength of nanotwinned copper samples with varying twin thicknesses. The authors examined nanotwinned copper with different twin thicknesses to assess strength variations. Strength peaks at a 15‑nm twin thickness, after which softer behavior with higher strain hardening and ductility appears, due to a shift from slip transfer across twin boundaries to activation of preexisting easy dislocation sources.

Abstract

The strength of polycrystalline materials increases with decreasing grain size. Below a critical size, smaller grains might lead to softening, as suggested by atomistic simulations. The strongest size should arise at a transition in deformation mechanism from lattice dislocation activities to grain boundary-related processes. We investigated the maximum strength of nanotwinned copper samples with different twin thicknesses. We found that the strength increases with decreasing twin thickness, reaching a maximum at 15 nanometers, followed by a softening at smaller values that is accompanied by enhanced strain hardening and tensile ductility. The strongest twin thickness originates from a transition in the yielding mechanism from the slip transfer across twin boundaries to the activity of preexisting easy dislocation sources.