Impact of the nickel interlayer on the electrical resistance of tin-tin interface submitted to fretting loading

The behaviour of the tin/tin interface for electrical contact application is addressed in this paper. Two coating systems were studied: a bronze-tin coating system and a bronze-nickel-tin coating system. The transition amplitude δt from partial slip (P.S) to gross slip (G.S), defining the domains of infinite and finite lifetime of the contact, was found using the variable-displacement-amplitude methodology (VDA). Constant-displacement-amplitude (CDA) tests were performed in order to determine the influence of the nickel interlayer on the performance of the electrical contact. The conducted analysis concluded that there is no influence of the nickel interlayer on the electrical endurance during G.S. However, the nickel interlayer, which serves as a diffusion barrier, eliminates the diffusion of copper through the tin coating; thus preventing the formation of copper oxides on the top surface. It concludes that the application of the nickel underlayer by maintaining high tin-tin friction coefficient extends the P.S domain and therefore increases the reliability of the electrical contact.