Answer
Fretting is a wear mechanism occurring at the contact points between the wave peaks and the mating surfaces (e.g., bearing races or housing shoulders) due to low-amplitude, high-frequency oscillatory movement. This movement removes the protective oxide layer of the metal, leading to localized pitting and the formation of abrasive debris. In wave springs, this can lead to stress risers and subsequent fatigue cracking. Mitigation strategies include: 1) Increasing the preload to minimize relative movement. 2) Applying dry-film lubricants (like $MoS_2$ or PTFE). 3) Surface hardening through nitriding. 4) Using materials like Phosphor Bronze or Copper-Beryllium for the spring if the mating surface is steel, as the dissimilar hardness reduces the rate of material transfer.
