Environment-Induced Deformation Localization During Transgranular Stress Corrosion Cracking

The nucleation and evolution of deformation patterns occurring during transgranular stress corrosion cracking (TGSCC) were studied in an attempt to produce new alternatives for addressing the nature of the embrittlement process. Flat, tensile α-brass (72% Cu-28% Zn) specimens were tested in 5 M aqueous ammonia (NH₄OH) solution at a strain rate of 1 x 10^–5 /s. Slip-band spacing (SBS) and slip-band height (SBH) were measured as a function of strain by conducting interrupted experiments in the SCC environment and were compared with those developed during laboratory air experiments. The presence of the TGSCC-causing environment during straining promoted localized plastic deformation at the near-surface region and, more importantly, produced an entirely different deformation pattern from that developed in laboratory air. The deformation evolved in the presence of the TGSCC electrolyte was highly localized, exhibiting small SBS but large SBH. Also, a periodicity was exhibited by the crack initiation process. The amount of localized strain developed at the specimen near-surface region before nucleation of stress corrosion cracks was found to be equivalent to the strain required for ductile fracture of the material in air, suggesting the existence of a fundamental fracture criterion. Grounds for an environment-induced deformation localization mechanism were introduced to explain the phenomenology of TGSCC initiation and propagation.