A number of studies(1,2,3,4) in recent years have pointed to the importance of the rate of repassivation to the mechanism of stress corrosion cracking (S.C.C.). The rationale of these studies is that, upon stressing, the passive oxide film that exists on a metal in a given environment fractures, and, unless its repair is sufficiently rapid, metal dissolution occurs at the film fracture site leading to crack initiation. Most of the studies directed at this problem have looked at straining electrodes measuring either current(2,3) or potential transients(4). One study utilized continual mechanical abrasion of the specimen surface to give dissolution kinetics of bare metal from current density measurements(5). One problem with these techniques has been that it is difficult to determine which part of the parameter measured, especially the current, is involved in film repair and which part is involved in metal dissolution — both anodic processes. Because of this, one cannot judge whether rapid initial current surges upon straining indicate rapid metal dissolution, rapid film repair, or some combination of both. It is only by looking at both processes, film growth and metal dissolution simultaneously, that we can sort out the role of repassivation of stress corrosion susceptibility.
