Contact resistance of oxidized metals dependence on the mating material.

The contact resistances of several oxidized metals were determined with smooth spherical probes that were made of various noble and base metals. It was found that contact resistance decreased sharply as the hardness of the probe was increased. Oxidized hard metal probes sometimes gave contact resistance which were less than those from probes made of soft noble metals. The reason is postulated to be that the plastic deformation, hence contact area, of a hard probe under mechanical load is less than that of one which is soft.