Correlation between Wear Resistance and Lifetime of Electrical Contacts

Electrical contacts are usually plated in order to prevent corrosion. Platings of detachable electrical contacts experience wear because of the motion between contacts. Once the protecting platings have been worn out, electrical contacts will fail rapidly due to corrosion or fretting corrosion. Therefore the wear resistance of the platings is a very important parameter for the long lifetime of electrical contacts. Many measures which improve the wear resistance can diminish the conductivity of the platings. Due to the fact that platings of electrical contacts must have both a high wear resistance and a high electrical conductivity, the manufacturing of high performance platings of electrical contacts poses a great challenge. Our study shows firstly the correlation between the wear resistance of platings and lifetime of electrical contacts and then the measures, which improve the wear resistance without impairing the electrical performance of the contacts. 1. Introduction Copper and copper alloys are the most widely used base materials for electrical contacts. Both copper and copper alloys are prone to corrosion and oxidation. Therefore electrical contacts are usually coated with protecting platings. The most extensively used coating materials are tin, silver, gold, palladium, nickel, and diverse alloys of these metals. Fretting is considered to be another major problem that affects the lifetime of electrical connectors. Different phenomena are related to fretting, such as fretting wear, fretting fatigue, fretting corrosion, insulating layer, and oxides [1–3]. Among these phenomena corrosion, insulating layer, and oxides are basically the direct cause of a major increase in contact resistance. The platings of nonprecious metals are generally prone to fretting corrosion. Therefore using metals which have little or no film-forming tendency, generally known as precious metals, as plating materials should be an effective measure to avoid failures caused by fretting. Gold is one of the most commonly used precious plating materials for high performance electrical contacts. Pure gold is very soft. When using gold as coating material, one of the limitations to their lifetime is the wear resistance of the plating material. This has been observed by some authors [1, 2]. Hard gold is usually used in order to improve the wear resistance of gold platings. The high degree of hardness is achieved by alloying elements such as cobalt, iron, or nickel. However, the effect of alloying elements is limited by the galvanic process and other surface properties, which are also