What causes fretting corrosion?

• A. A chemical reaction with moisture in the air.
• B. Electrical arcing between wiring under load.
• C. A subtle fatigue crack due to vibration over time.
• D. A slight vibration, friction, or slippage between two contacting surfaces that are under stress or heavy load.

Answer: (D)

Fretting corrosion happens when two metal surfaces that are under load rub or slip against each other in a very small, repetitive motion. That tiny oscillation wears away the protective oxide film at the contact area, exposing fresh metal to the environment. As the fresh metal reacts electrochemically, especially in the presence of moisture or ions, corrosion accelerates right where the surfaces are rubbing. The wear debris and altered local chemistry further trap electrolytes, creating a localized, accelerated corrosion zone that can lead to pits, cracks, and eventual failure. This combination of mechanical wear and electrochemical attack distinguishes fretting from mere moisture-driven corrosion, arcing, or fatigue crack growth due to vibration.