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·
Different
electrode potentials may be induced in a material by regions of different
defect concentration.
· Grain
boundaries have atomic binding energies different than the bulk material.
They behave as anodes with respect to the bulk. Grain boundary corrosion
rates will be higher than the bulk rates.
·
Cold
working increases the dislocation density and introduces local residual
stresses, both processes changing the local free energy. These regions
will be anodic with respect to the bulk material and behave as anodes in
a corrosion environment.
·
The
lower diagram shows corrosion zones produced by bending, and by cold working
a material to form nails from a wire stock. |
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