How does fretting corrosion at the wave peaks of a wave spring lead to fatigue failure in reciprocating pumps?

In reciprocating pumps, the wave spring undergoes constant micro-deflections. This causes 'fretting' at the contact points (the peaks) where the spring rubs against the mating plates. Fretting removes the protective oxide layer of 17-7PH, leading to localized pitting. These pits act as severe stress concentrators ($K_t$). The failure manifests as a crack propagating from the peak through the radial wall. To prevent this, the contact surfaces should be hardened to at least 50 HRC, or a dry-film lubricant (e.g., MoS2) should be applied to the spring to reduce the coefficient of friction and the rate of surface degradation.