In situ observation fracture propagation of freestanding ultra thin buckling tungsten film

摘要

Crack propagation in sputter-deposited freestanding nanocrystalline tungsten films with a thickness of 38nm was studied using an in situ transmission electron microscopy (TEM) tensile technique.The residual stress and structural properties of tungsten thin films prepared by magnetron sputtering is reported.It is found that the residual stress, surface morphology, and fracture mode is clearly correlated.We estimated residual stress according to film parameters such as film thickness and Young modulus.The generation mechanism of residual stress and the emergence of telephone cord buckling pattern is discussed.We have compared the fracture propagation mode of telephone cord pattern buckling films and non-buckling films.Distinct from non-buckling film, which exhibit toughing mechanisms and intergranular fracture without cleavage, the buckling film show evident characteristic of brittle rupture, such as cleavage and rapid crack propagation a sharp crack tip.This difference may be ascribed to the effect of residual stress in buckling films, which can lead to lattice distortion.Lattice distortion can inhibit the dislocation motion and result in the cleavage.Cleavage fracture is easier to appear when dislocation movement is hindered.The comparative study shows that residual stress plays a very important role in the process of film fracture.