Length scale dependent yield strength and fatigue behavior of nanocrystalline Cu thin films

The length scale dependent mechanical fatigue behaviors of nanocrystalline (NC) Cu thin films were systematically investigated in terms of the yield strength related deformation mechanisms. Maxima are observed for both the yield strength and fatigue lifetime. The variation of strength as well as the changes of fatigue damage suggests the deformation mechanism transition from dislocation-based to grain boundary-mediated as the characteristic dimensions reduce down to below a critical value. The optimized fatigue properties can be achieved by best combination strength and ductility.