LAUSR

Abstract This work investigated the effect of an 850-nm-thick electroplated Au coating on the very high cycle bending fatigue behavior of electroplated Ni microbeams tested under resonance in air at high frequencies (∼9 kHz). The S N curves show longer fatigue lives for the coated microbeams by at least a factor of 5 compared to the uncoated ones. This beneficial effect is demonstrated to be related to the delay in oxygen-assisted void formation, and therefore in void-assisted fatigue crack nucleation and growth in Ni. The improvement in fatigue life is limited by the fatigue degradation of the Au coating, which is also controlled by the formation of nanosized voids. Once a fatigue crack in the coating reaches the interface, delamination occurs, leading to exposure of the underlying Ni to air and faster, “uncoated-like”, fatigue degradation thereafter. This study highlights that thin, noble metal coatings can significantly improve the fatigue lives of metallic microbeams whose very high cycle fatigue behavior is sensitive to the environment and controlled by void formation.