Revealing the Maximum Strength in Nanotwinned Copper
L. Lu,1*
X. Chen,1
X. Huang,2
K. Lu1
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.
2 Center for Fundamental Research: Metal Structures in Four Dimensions, Materials Research Department, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, DK-4000 Roskilde, Denmark.
* To whom correspondence should be addressed. E-mail: llu{at}imr.ac.cn
