Third bodies in electrical contacts — Wear and electrical performance

Silver is a widely used protective coating material in electrical connectors, since it has good resistance to oxidation and thus is not affected by corrosion and fretting corrosion. The dominating mechanism for failure in silver coated electrical contacts is fretting wear. Recently, wear between silver-silver contacts has been analyzed and adhesion is recognized as the dominating mechanism during the wear process. According to our experiments, the distribution of third bodies in the contact area also has great influence on the lifetime of electrical contacts, since it can greatly influence the condition of contact surfaces. In this paper, two arrangements of samples, namely "sphere on plate" and "plate on sphere" are used to generate different distribution of third bodies. Depending on the arrangement of electrical contacts, the amount of remaining debris in the contact area produced by fretting of electrical contacts varies largely. As a result, should a large amount of debris remain in the contact area, the third bodies (the debris) change the tribological conditions significantly. This leads to a marked increase in the wear of the coating which in turn reduces the lifetime of electrical contacts considerably. A model of the mechanism of the influence of third bodies is introduced and verified by experiments. This paper provides indications for design, characterization and fretting corrosion measurements. The arrangement of samples has to be specified and "sphere on plate" is the more critical case.