Q: What are Fretting and Inter granular Corrosion? A: FRETTING 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 their axles. 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. INTERGRANULAR CORROSION: Selective dissociation/attack of grain boundaries with no significant attack of the grains. Exfoliation is an extreme example. 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.