Analysis of Fretting Behavior of Silver and Gold Flashed Palladium-nickel Dissimilar Coatings for Connectors

It is well known that good wear performance can be obtained with Au-flashed palladium-nickel sphere on flat contacts simulating various connector applications. It has also been shown that these good wear properties could be recorded for asymmetrical coatings such as a noble metal sphere on Au-flashed palladium-nickel. In this paper we investigate the fretting properties of such asymmetrical coatings particularly of Ag versus Au flashed PdNi. The contacts are submitted to severe fretting wear by applying imposed sine displacements of amplitude similar to the Hertz contact radius. The contact resistance, the friction force and wear evolutions were analyzed and correlated to 3D profllometry measurements allowing wear volumes quantification and EDS elemental identification of the wear tracks. Very different behaviors are observed whether the silver coating is on the sphere or on the plane though in both case the embedding of the oxidized wear debris by silver improves the fretting behavior. The transfer of silver from the sphere contact onto the palladium nickel flat is seen to be beneficial to the electrical stability of the interface for a long time, leading to more stable results than even silver/silver contacts. Nevertheless an unusual phenomenon of the galling type is observed for which more investigations are needed.