Meaning
Physical corrosion mechanisms describe the mechanical exposure of bare metal surfaces through localized fracture of protective oxide coatings during cyclic or monotonic strain. Metallurgical failure analysts evaluate dynamic film rupture to explain crack initiation in subsea pipelines and industrial pressure vessels. The phenomenon occurs when mechanical strain rates exceed the deformation capability of the surface passive film.
The mechanism ceases when mechanical strain stops or when environmental conditions prevent film reforming.
Strain Rate
Mechanical deformation creates localized slip steps that fracture thin surface oxide layers. Microscopic surface steps expose bare metal directly to surrounding corrosive solutions, initiating rapid anodic dissolution. Fast strain rates cause rapid film fracture before surface repassivation can restore protective barriers.
Slow strain rates allow continuous film repair, preventing severe localized corrosion attack.
Oxide Repassivation
Solution chemistry determines how quickly exposed bare metal reforms a protective oxide layer. Rapid repassivation limits metal loss at exposed slip steps, suppressing crack growth rates. Slow repassivation in acidic or high-chloride environments allows continuous anodic dissolution along grain boundaries.
Laboratory measurements of repassivation current density quantify alloy resistance to environment-assisted cracking.
Crack Propagation
Continuous cycles of film fracture and localized dissolution drive crack growth through structural components. Engineering models calculate critical strain limits to prevent environmental crack growth.
