Fretting Corrosion

A mechanical damage process which occurs when the high points (asperities) on one surface are moved over and adhere to the asperities (or high points) or another surface. Although a metal surface may look flat and even polished when magnified especially at very high levels of magnification, small “mountains” and “valleys” exist on the surface. When two pieces of metal slide or are rubbed over each other those “mountains” (asperities) contact each other. The result is that metal from one surface is rolled up, broken off and sometimes is transferred to the other surface. Thus fretting is categorized as a corrosion process. Fretting corrosion occurs when one surface of two metal objects which are moving over one another (usually without lubrication) sticks or adheres to the other surface resulting in metal transfer. Under some circumstances the small pieces of fretted metal merely become oxidized and appear as a powder or dust.