How can 'Fretting Corrosion' be identified on a wave spring, and what design changes mitigate this in vibrating environments?

Fretting corrosion appears as reddish-brown (for steel) or black (for stainless) debris at the contact points between the wave peaks and the mating surfaces. It is caused by microscopic oscillatory movement (slip) under load, often due to high-frequency vibration. Under SEM (Scanning Electron Microscopy), the surface will show small pits and oxide build-up. Mitigation strategies include: 1) Increasing the axial preload to prevent 'lift-off' and slip, 2) Applying a dry-film lubricant (e.g., $MoS_2$) to reduce friction, or 3) Increasing the number of waves $n$ to distribute the load across more points, thereby reducing the local contact pressure.