Localized surface plasticity during stress corrosion cracking

A previously proposed stress corrosion cracking (SCC) mechanism incorporating localized surface plasticity (LSP), crack initiation, and crack-tip embrittlement by anodic dissolution at film rupture sites is reviewed, together with new information supporting the mechanism Externally imposed anodic dissolution currents increase creep rates of pure metals and alloys. Creep prior to SCC has been observed frequently and may result from anodic currents at active film rupture sites caused by coupling to surrounding noble passive surfaces. Recently revealed correlations between creep rate and SCC failure times imply that mechanisms of creep and cracking may be related. Anodic attenuation of strain hardening at film rupture sites may cause LSP, leading to triaxial stress conditions, suppressed slip, and crack initiation. Recent thin-film diffusion experiments show evidence of vacancy formation at anodically dissolving Cu surfaces. It has been suggested that anodically generated vacancies may increase creep and plasticity by stimulation of dislocation climb or by attraction to dislocation cores. Point-defect vacancies may weaken the crystal lattice, as do point-defect H atoms in the decohesion mechanism popular for explaining hydrogen embrittlement (HE).