Fretting Behavior of Nickel Coatings for Electrical Contact Applications

Fretting remains a major cause of connector failure and can impair reliability in complex systems. Oxidizable metals such as tin, copper and nickel are particularly prone to fretting degradation. We report here the first results of an investigation on fretting of nickel contacts with two types of deposits. Sulfate nickel layers are electrodeposited in different conditions and show very different behaviours during fretting tests. The characteristics of the layers are analyzed and show different compositions and microstructures. The compositions are measured by X-Ray Photoelectron Spectroscopy (XPS) which allows determining the chemical nature of the compounds formed during exposure to air. Topography is measured by AFM and the roughness and grain characteristics are assessed. Electrical properties at the micro/nanoscale are measured with the CP-AFM technique. Various loads are applied to the cantilever beam; the electrical characterization is performed versus the load. The results of fretting experiments are analyzed in terms of fretting regimes. The fretting regimes occurring during the test of the matte layers involve partial slip which delays the occurrence of contact resistance (Rc) increase. Gross slip in the interface is shown to create very poorly conducting wear debris leading to drastic increase of Rc. This study is part of a larger one aiming at tailoring coatings allowing the best tribological and electrical behaviors during fretting of nickel contacts.