Superior fatigue crack growth resistance in bulk Cu with highly oriented nanotwins

We studied the fatigue crack growth (FCG) characteristics of bulk nanotwinned Cu (NT-Cu) with different microstructural aspects such as grain size and twin thickness. We specifically addressed the crack closure, with particular emphasis on the intrinsic FCG resistances in the near-threshold regime. The results demonstrate that the NT-Cu samples have significantly improved fatigue resistances compared with conventional twin-free polycrystalline Cu, a fact we measured using the effective threshold stress intensity factor range, Delta Kth,eff. This enhanced resistance can be traced back to the activation of a specific set of primary slip systems in the NT-Cu, known as special trans-twin dislocation, which dominates the crack-tip cyclic deformation, leading to a diminished level of cyclical slip irreversibility and, in turn, enhancing the inherent resistance to damage propagation.