Influence of contact interface composition on the electrical and tribological properties of nickel electrodeposits during fretting tests

Oxidizable metals such as tin, copper and nickel are largely used to manufacture connectors or electrical contacts. They have been shown to be particularly prone to fretting degradation. In a recent investigation we have shown that nickel coatings electrodeposited in different conditions could display different fretting behaviors. The characterization of the coatings showed the influence of two main parameters: the grain size and the surface composition. In this paper we present an extensive study of the fretting wear tracks of the different coatings performed by XPS and AES. Then the electrical and mechanical behaviors of the coatings are investigated when a PFPE lubricant film is added. The wear scars are analyzed and allow giving a scenario for the degradation which can be correlated to the evolution of the contact resistance values measured during the test. In the case of matte nickel coatings a medium value of Rc is maintained for several thousands cycles. The choice of lubricant with its branched structure is thought to be favorable to the grafting of a thin inert fluorinated film postponing the degradation and the oxidation of the coatings.