Effect of Normal Forces on the Electrical Endurance of Tin-Plated Contacts Under Elevated Temperature Fretting Conditions

In this article, an attempt is made to explore the effects of normal force and temperature on the threshold displacement amplitudes of tin-plated electrical contacts at elevated temperatures. Fretting tests were conducted at 323, 348, and 373 K at normal forces of 1, 1.25, 1.5, and 2 N. Riders and flats made from a 0.3-mm-thick brass sheet were coated with $10~\mu \text{m}$ of tin. Dimples were commonly found at the center of the contact area of the test specimens corresponding to an unlimited lifetime. In the testing temperature range, the threshold displacement amplitude decreases with an increase in the temperature and with a decrease in the normal force. In this range, the threshold displacement amplitude was found to be controlled by the oxidation of a tin-plated surface. The activation energy was found to be 7.5 kJ/mole, which is close to the value of the activation energy for the growth of tin oxide film. The threshold displacement amplitude can be represented in the form of an Arrhenius equation and is proportional to the normal force.