MECHANISTIC STUDIES OF STRESS-CORROSION CRACKING - APPLICATION OF THECORROSION-ASSISTED CLEAVAGE MODEL TO RESULTS USING ORIENTED SINGLE-CRYSTALS

Stress corrosion experiments were carried out on oriented single cryst als of copper-gold and copper-zinc (alpha-brass) using constant and sl ow strain rate (SSR) loading modes under various chemical conditions i n which passive oxides were present on the surface or dealloying occur red in the absence of such films. Results supported the role of locali zed dissolution at slip traces in crack initiation at free surfaces as well as in the renucleation of arrested cracks. Orientations of fract ure surfaces were predominantly {110} independent of the tensile axis orientation, with the occasional appearance of {111} fracture planes i n 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 sur faces. Dissolution in a cuprous ammonia solution in equilibrium with c opper 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 chara cteristic surface morphology of transgranular stress corrosion crackin g (TGSCC) surfaces. Results were reviewed in terms of applicability of the corrosion-assisted cleavage (CAC) model.