Quantification of the electrical contact endurance of thin platted silver coatings subjected to fretting wear: Influence of coating thickness

Materials used in the connectors in cars are expected to have very low and stable electrical resistance and high resistance against corrosion. The environmental and mechanical factors strongly influence mentioned parameters. Thus numerous coating systems consisting of pure metallic materials, noble and non noble, doped as well as soft coatings were developed and studied. In this work the degradation mechanisms of homogeneous bronze/nickel/silver coatings systems were studied under fretting loadings. Five silver layer thicknesses (1.3μm, 2μm, 3μm, 4μm and 5μm) were investigated. Different test procedures have been applied to identify first the transition from partial to gross slip conditions and establish the electrical endurances as a function of the applied displacement amplitudes in the finite endurance gross slip condition. Very basic criteria have been introduced to rationalize and compare the electrical endurance as a function of the coating thickness. It is shown that the evolution of the electrical endurance vs. the coating thickness displays a nearly linear increase above a threshold coating thickness. Below this threshold, silver was found to delaminate from nickel interlayer in the very earlier stage of the test inducing very short electrical endurance.