Corrosion-enhanced dislocation emission and motion resulting in initiation of stress corrosion cracking

Abstract

A special constant deflection device for TEM has been designed, and then change of dislocation configuration ahead of a crack tip during stress corrosion cracking (SCC) of brass in water and of Ti−24Al−11Nb alloy in methanol and initiation of SCC can be observed in TEM.In situ tensile test in TEM for brass was carried out for comparison. The results show that anodic dissolution during SCC can facilitate dislocation emission, multiplication and motion, and a dislocation free zone (DFZ) is formed. The stress at a particular site in the DFZ, which is an elastic zone and is thinned gradually through corrosion-enhanced dislocation emission and motion, is possibly up to the cohesive strength, resulting in initiating of a nanocrack of SCC in the DFZ or sometimes at the crack tip. Because of the action of the corrosion solution the nanocrack of SCC propagates into a cleavage or intergranular microcrack rather than blunts into a void likein situ tension in TEM.