What are Fretting and Inter granular Corrosion?
- Small amplitude oscillation in a corrosive medium.
- Examples are press fit wheel on a shaft, turbine
blades in dovetail slots, railroad car wheel shrink fit to
- Oxidation is the "corrosion" film
removed by the
mechanical motion, becoming an abrasive.
- The illustration below shows fretting corrosion on
the root surface of an aircraft power plant compressor
blade. Fatigue cracks can initiate as a result of this
fretting pitting damage.
- Selective dissociation/attack of grain boundaries with no
significant attack of the grains. Exfoliation is an extreme
- Galvanic cell forms between grain and drastically
different composition of the boundary -- possibly due
to precipitates under service conditions or heat treatment.
- Many other examples. For instance, in 304SS-precipitation
of Cr carbides, e.g., (Cr, Fe) 23 C6, at grain boundaries,
with Cr depleted regions next to them. Al alloys also
experience this effect.