Fretting corrosion is most likely to occur

• A. Surfaces are smooth
• B. At high temperatures
• C. Two surfaces fit tightly together but can move relative to one another
• D. In complete isolation

Answer: (C)

Fretting corrosion happens when there’s small-scale sliding between surfaces that are in contact under load. The key factor is the micro-movement at the contact points, which disrupts protective oxide films and exposes fresh metal to the environment. When two surfaces fit tightly together but can move slightly against one another, those tiny motions continually wear the surface and promote corrosion in the worn spots. If there’s no contact or no relative motion, fretting doesn’t occur, and while high temperature can affect corrosion processes, it doesn’t define fretting by itself.