A possible degeneration mechanism in stationary electrical contacts

A mechanism for the degeneration of stationary electrical contacts is proposed. The mechanism derives from Mullins´ model (1959) of flattening of free surfaces through the action of capillarity forces. Mass transport for surface deformation is assumed to occur through volume self-diffusion and is calculated on the basis of diffusion constants characteristic of plastically deformed or mechanically stressed aluminium. A simple electrical contact model suggests that the increase in contact resistance stemming from surface flattening in Al at room temperature can become noticeable in a time interval of a few days (~10⁶ s). This result may explain the deterioration of contaminated Al/Al stationary electrical contacts operated at room temperature, after run-times of 10⁵-10⁶ s. Finally, since many metals are characterized both by rapid volume or surface diffusion and by a large surface energy, the results suggest that asperity flattening can lead to degeneration in all bulk electrical interfaces