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 att empt to produce new alternatives for addressing the nature of the embr ittlement process. Flat, tensile alpha-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) w ere measured as a function of strain by conducting interrupted experim ents in the SCC environment and were compared with those developed dur ing laboratory air experiments. The presence of the TGSCC-causing envi ronment during straining promoted localized plastic deformation at the near-surface region and, more importantly, produced an entirely diffe rent deformation pattern from that developed in laboratory air. The de formation 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 st rain developed at the specimen near-suface region before nucleation of stress corrosion cracks was found to be equivalent to the strain requ ired for ductile fracture of the material in air, suggesting the exist ence of a fundamental fracture criterion Grounds for an environment-in duced deformation localization mechanism were introduced to explain th e phenomenology of TGSCC initiation and propagation.