What are visible signs of fretting corrosion?

Fretting corrosion is a specific type of wear and corrosion that occurs at the interface of materials that are in close contact and subjected to motion or vibration. The visible signs of fretting corrosion typically include a dark, smoky appearance of corrosion residue. This residue results from the interaction between the two surfaces where slight relative motion causes abrasive wear and subsequent corrosion.

The dark appearance is a result of fine particles being generated from the wear process, which can trap moisture and other contaminants, leading to corrosion. This contrasts with other types of corrosion that might display features such as thick rust layers, bright metallic shine, or distinct greenish oxide formations, which are more representative of other corrosion processes like rusting of iron or copper corrosion. Understanding these characteristics helps in identifying and addressing the issue promptly in aviation maintenance practices.