Fretting corrosion behavior of electrical contacts with tin coating in atmosphere and vacuum.

Electrical contacts are basic components of electrical systems. They are applied in various conditions, which can influence the lifetime of the electrical contacts significantly. Fretting corrosion is one of the main failure mechanisms of electrical contacts with micro-motion. During this operation, the coating on electrical contacts is worn, generating wear debris. If the coating consists of non-noble material, for instance tin, which is a widely used coating material for electrical contacts, the wear debris will be oxidized and subsequently form an electrically highly resistant oxide layer after long-term service. Two decisive factors for the lifetime of electrical contacts are the number of cycles of motion and the time required to form this thick oxide layer. In many power semiconductor components, the housing is firstly pumped to vacuum condition, and then filled with nitrogen. The higher degree of vacuum leads to a substantially reduced amount of oxygen, a lower oxygen partial pressure and a longer mean free path of oxygen molecules, which retards the oxidation process. Therefore a remarkable improvement of fretting corrosion behavior is theoretically expected. The subject of this study is to investigate the effects of atmosphere and vacuum on fretting corrosion behavior. In order to investigate the fretting corrosion performance and the lifetime of these tin coated electrical contacts, a series of wear and fretting corrosion tests are conducted under various degrees of vacuum. The correlation between the lifetime of electrical contacts and pressure is analyzed. The results indicate that with an increasing degree of vacuum, the lifetime of electrical contacts in fretting tests is, as expected, prolonged. • The higher vacuum level leads to a remarkable improvement in fretting corrosion behavior of tin coated electrical contacts. • A relationship between the oxygen partial pressure and the lifetime is proposed based on theoretical derivation and then verified by the experimental data. • The lifetime can be significantly influenced by the vacuum condition. • It is possible to predict the lifetime of tin coated electrical contacts under various vacuum conditions. • The common model of fretting corrosion can be validated quantitatively by the results of this study. [ABSTRACT FROM AUTHOR]