Wear or Rust? That’s Fretting Corrosion!

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Wear or Rust? That’s Fretting Corrosion!

Last updated on Jan 01, 2026

It’s common to find wear on the contact surfaces of two components even when there seems to be no obvious relative movement—for example, wear between the outer ring of a bearing and the bearing housing bore shown below.

Even when components are lubricated and have no relative movement, rust-like marks can appear quickly, such as the "red rust-like traces" at spline fits in the image below.

What’s happening here? This is what we’re going to explore today: **Fretting Corrosion**.

Fretting corrosion refers to progressive surface damage occurring at the contact area of two metals. It is caused by extremely slight oscillating, vibrating, or sliding movements between metal surfaces (even amplitudes as small as nanometers can trigger it), combined with corrosive attack from the environment.

(Before and after fretting corrosion: Exposed metal → Oxide layer → Oxide particles)

The most common environmental factor is oxidation. When fretting occurs between two components, the metal at the contact high points deforms and peels off into fine particles from the surface through mechanical cyclic motion. These particles are then oxidized and trapped between the fretting surfaces. Some settle in the low-lying areas of the contact surfaces, while others act as abrasives, increasing the material removal rate. If a new passive film cannot form promptly after metal wear, the damage will intensify.

The above is the basic principle of fretting corrosion. So how can we prevent it?

1. Prevent "fretting" first

This may include design modifications, selecting appropriate tolerances, improving fit accuracy, suppressing any possible vibration, and ensuring all joints are properly tightened.