LOCALIZED SURFACE PLASTICITY DURING STRESS-CORROSION CRACKING

A previously proposed stress corrosion cracking (SCC) mechanism incorp orating localized surface plasticity (LSP), crack initiation, and crac k-tip embrittlement by anodic dissolution at film rupture sites is rev iewed, together with new information supporting the mechanism External ly imposed anodic dissolution currents increase creep rates of pure me tals and alloys. Creep prior to SCC has been observed frequently and m ay result from anodic currents at active film rupture sites caused by coupling to surrounding noble passive surfaces. Recently revealed corr elations between creep rate and SCC failure times imply that mechanism s of creep and cracking may be related. Anodic attenuation of strain h ardening at film rupture sites may cause LSP, leading to triaxial stre ss conditions, suppressed slip, and crack initiation. Recent thin-film diffusion experiments show evidence of vacancy formation at anodicall y dissolving Cu surfaces. It has been suggested that anodically genera ted vacancies may increase creep and plasticity by stimulation of disl ocation climb or by attraction to dislocation cores. Point-defect vaca ncies may weaken the crystal lattice, as do point-defect H atoms in th e decohesion mechanism popular for explaining hydrogen embrittlement ( HE).