Direct Observation for the Effect of Electric Current on Contact Interface

The conditions of the contact interface affect contact resistance characteristics. Therefore, information of the contact interface is very important for the study of contact performance. However, a real contact area, which carries the electric current path, is quite small. If the area can be observed directly, much information of the contact interface will be obtained. Such an investigation has not been performed for electric contacts energized by current. The experimental and technical realization of the equipment for measuring and directly observing the characteristics of contact interface energized by current is described. It is composed of an automatically contact-making apparatus, conductive transparent electrodes, and an inverted type metallurgical microscope. Investigations were carried out for various kinds of contact materials from the viewpoint of how the flowing current affects the interface of real contact area. The real contact area increases markedly by Joule heating when the temperature in the area rises to the recrystallization temperature peculiar to metals. The softening temperature agrees with the recrystallization temperature. Sulfide films deform due to softening. This softening of the films causes !ow contact resistance characteristics.