Electrical fretting wear performance of new silver composite coatings

In transport applications (automotive, aviation), the increase of electronic devices promotes an extensive use of electrical connectors which need to maintain a low and stable electrical contact resistance. However, they are subject to vibration, which can cause severe fretting wear damage in the contact, leading to increased electrical contact resistance and decay of information transmission. Presently, the main solution consists in applying noble coatings (Ag, Au), although, due to the price of gold, Ag layers are preferred. However, some improvements remain to be made in order to match the performance of gold, and this implies developing new silver composites displaying better electrical performance and lower wear rates. In the present study, several new Ag-based coatings including various doping particles (CrN, C, etc.) were investigated to determine the benefit of composite layers for connectors such as in electrical micro-contact applications. A homogeneous crossed-cylinder configuration was studied under gross slip conditions, varying the fretting loading (±2μm<;δg*<;±16μm, P=3N, RH=10%, T=25°C and f=30Hz). Simple expressions were derived to quantify the Electrical Contact Resistance (ECR) endurance evolution (Nc: ΔR>δRc=4mΩ) as a function of fretting sliding and coating structure. The studied layers were thus classified according to ECR performance. Chemical and 3D profile investigations were also performed, to describe the ECR degradation process.