Mechanistic studies of stress corrosion cracking: Application of the corrosion-assisted cleavage model to results using oriented single crystals

Stress corrosion experiments were carried out on oriented single crystals of copper-gold and copper-zinc (alpha-brass) using constant and slow strain rate (SSR) loading modes under various chemical conditions in which passive oxides were present on the surface or dealloying occurred in the absence of such films. Results supported the role of localized dissolution at slip traces in crack initiation at free surfaces as well as in the renucleation of arrested cracks. Orientations of fracture surfaces were predominantly {110} independent of the tensile axis orientation, with the occasional appearance of {111} fracture planes in alpha-brass. Common fractographic features were seen in all systems studied, including the presence of crack-arrest markings. Dissolution of alpha-brass in cupric ammonia solutions produced faceted pits with characteristic morphologies reflecting the symmetry of the exposed surfaces. Dissolution in a cuprous ammonia solution in equilibrium with copper produced minimal attack and no pitting. None of the morphologies for specimens corroded in the nonequilibrium or equilibrium solutions, with or without static or dynamic loading, were similar to the characteristic surface morphology of transgranular stress corrosion cracking (TGSCC) surfaces. Results were reviewed in terms of applicability of the corrosion-assisted cleavage (CAC) model.