Transmission electron microscopy observations of deformation and fracture in nanolaminated Cu-Ni thin films

Deformation and fracture of nanolaminates have been investigated by in-situ transmission electron microscopy (TEM) straining of cross-sectioned epitaxial Cu/Ni nanolaminates grown on Cu(001) single-crystal substrates. Initial deformation is accommodated by confined layer slip. With continued straining, unstable fracture occurs, creating a mixed-mode crack that propagates across the nanolaminate interfaces. Further straining results in stable crack growth with intense plastic deformation ahead of the crack tip extending over many bilayers in the direction of crack growth. However, the plastic zone is confined within a small distance normal to the crack. Post-mortem TEM, in general, did not reveal the presence of dislocations in the crack wake, except when the crack was deflected. By comparison, the plastic zone size in the substrate was greater by several of orders of magnitude.