Scope of Environment-Sensitive Fracture

Material/Environment Variables Affecting Crack Initiation and Growth 

A limitation to associating stress-cracking tendencies with potential regions as represented by Fig. 7.71 is that the ranges indicated relate to potentials measured at the surface under either freely corroding conditions or potentials established by a potentiostat or other external 

Fig- 7.72 Schematic representation of stress induced surface profiles representative of the potential ranges identified in Fig. 7.71. (a) Hydrogen embrittlement, (b) Active corrosion, (c) Passive film cracking, (d) Passivity, (e) Pit-initiated cracking 

Fig- 7.73 Schematic representation of (a) passive film, (b) passive film rupture by stress-induced slip resulting in exposure of bare substrate, (c) crack initiation by anodic dissolution initiating crevice corrosion conditions before repassivation of exposed substrate, and (d) repassivation of exposed substrate before crack initiation. 

Potential ranges of susceptibility to SCC also have been identified by determining the polarization curve during rapid straining (e g., at strain rates of the order of 10 2 s ). A shift of the polarization curve to larger 

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