In-situ transmission electron microscopic observation of corrosion-enhanced dislocation emission and crack initiation of stress corrosion

A constant deflection device designed for use within a transmission electron microscope (TEM) was used to study the change in dislocation configuration ahead of a crack tip during stress corrosion cracking (SCC) of brass in water, Ti-24% Al-11% Nb alloy in methanol (CH3OH), and the initiation of SCC. In-situ tensile tests in the TEM also were carried out to assess deformation without the influence of environment. Results showed that corrosion during SCC enhanced dislocation emission, multiplication, and motion as well as produced a dislocation-free zone (DFZ). Nanocracks of SCC initiated in the DFZ or from the crack tip when the corrosion-enhanced dislocation emission and motion reached a certain condition. The action of the corrosion process prompted nanocrack propagation into a cleavage or intergranular microcrack rather than blunting into a void as seen during experiments in the TEM