Fretting corrosion is likely to occur when what conditions are met?

Fretting corrosion is a specific type of wear that occurs at the interface of two materials that are in contact, especially when there is relative motion between them. When two surfaces fit tightly but can still move relative to one another, the movement causes microscopic wear and displacement of material at the contact points. This movement can create small fretting wear particles and a wear debris layer that disrupts the protective oxide layers on the materials, leading to increased surface reactivity and corrosion.

In this scenario, the tight fit helps maintain contact between the surfaces, while the relative motion induces stress at the interface, promoting localized corrosion. Fretting corrosion is particularly problematic in many applications, including aircraft components, where the combination of pressure and minor movements can lead to significant material degradation over time.

Other situations, such as two surfaces being loose and movable, may not lead to fretting corrosion because there wouldn't be enough consistent contact or stress to generate corrosion in the same way. Similarly, a lack of lubrication or exposure to moisture alone does not directly cause fretting corrosion without the additional factor of relative motion under contact pressure.