CORROSION-ENHANCED DISLOCATION EMISSION AND MOTION RESULTING IN INITIATION OF STRESS-CORROSION CRACKING

A special constant deflection device for TEM has been designed, and th en change of dislocation configuration ahead of a crack lip during str ess corrosion cracking (SCC) of brass in water and of Ti-24Al-11Nb all oy in methanol and initiation of SCC can be observed in TEM. In sirte tensile test in TEM for brass was carried out for comparison. The resu lts 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 e lastic zone and is thinned gradually through corrosion-enhanced disloc ation emission and motion, is possibly up to the cohesive strength, re sulting 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 na nocrack of SCC propagates into a cleavage or intergranular microcrack rather than blunts into a void like in situ tension in TEM.