Simulation Methodology for Prediction of the Wear on Silver-Coated Electrical Contacts With a Sphere/Flat Configuration

A protective coating is generally applied on base materials for better performance and a longer lifetime of electrical contacts. Silver is a widely used coating material, due to the good balance between the high resistance to corrosion caused by oxidation and the cost. Moreover, it possesses high electrical conductivity. Before the wear through of silver coatings, the electrical contact resistance is stable and remains at a low value, and thus, the reliability of electrical contacts can be guaranteed. After the wear through of silver coatings, the base material, typically a copper alloy, is exposed to the environment. The oxides of base materials are generated and accumulated, leading to blocking of the current path and an electrical failure of the contacts. Consequently, it is critical to predict the wear through of the silver coatings, when assessing the reliability of the electrical contacts. However, for a thick coating, it is difficult to forecast the wear through, since the linear wear rate of coatings decreases disproportionately with increasing coating thickness, and various phases exist, such as the running-in phase and the steady-state phase. In this paper, a simulation methodology based on Archard's wear equation and consideration of both the surface roughness and geometry of the contact area is established in order to interpret the wear process of thick silver coatings with an as-received roughness applied in the electrical contacts with a sphere/flat configuration. The specific wear coefficient is regressed by curve fitting, according to the experimental results in the running-in phase and results from finite element analysis computation. Then, a modification of the regressed specific wear coefficient is conducted, considering the simplification of the roughness on the flat part and the gaps on the roughness ribs introduced by the rolling process. This modified specific wear coefficient is applied in the calculation model for the steady-state phase in order to predict the wear through of silver coatings. A good correlation between the simulated wear curve and the experimental results is obtained.