In-situ observation of crack propagation through the nucleation of nanoscale voids in ultra-thin, freestanding Ag films

A tensile technique was developed and coupled with in-situ transmission electron microscopy observations to directly characterize the crack propagation mechanism in sputter-deposited, ultra-thin, freestanding nanocrystalline Ag thin films with a thickness of 60 nm. The developed technique directly revealed the fracture mechanism; the thin film with nanoscale grains exhibits ductile fracture behavior, and the crack propagates through void nucleation, growth, and coalescence ahead of the crack tip. A model for the energy release rate during the propagation of nanovoids was established to quantitatively characterize the equilibrium length of the voids. Based on experimental measurements and theoretical calculations, the effects of stress distribution and energy transformation on the nucleation position, equilibrium length, and growth rate of the nanovoids are discussed.