What causes fretting corrosion?

Fretting corrosion arises primarily due to slight relative motion between two mating surfaces. When two surfaces come into contact but experience vibrations or small movements, this can lead to the rubbing together of the surfaces, disrupting any protective oxide layers that might have formed. This mechanical action exposes the bare metal beneath, which is susceptible to corrosion as it is no longer protected from environmental factors like moisture and air.

This form of corrosion is particularly problematic in areas where components are constrained, such as bolted joints or bearings, where movement can be minimal yet significant enough to cause wear over time. The combination of this micro-movement and environmental exposure leads to localized damage, pitting, and eventually, material degradation.

The other options reference conditions that can cause corrosion but do not specifically address the mechanism of fretting corrosion as effectively as the slight relative motion. For example, high temperatures and chemical reactions may lead to different forms of corrosion, direct exposure to saltwater typically contributes to electrochemical corrosion processes, and excessive pressure on a point can cause deformation or stress failure rather than the mechanical wear that typifies fretting corrosion.