Part I. Friction of metals - Influence of oxide films on metallic friction

Abstract

The mechanism of metallic friction, in air, has been investigated for loads ranging from 0.003 to 10000 g. The metals studied include platinum, gold, silver, copper, tin, lead, zinc, cadmium, magnesium, aluminium and chromium. The earlier work of Whitehead has been extended and simultaneous measurements made of the frictional force and the electrical resistance between the sliding surfaces. The results show that with most metals the natural oxide layer is sufficient to prevent metallic contact at very small loads. The degree of protection depends on a number of factors, such as the surface roughness, the thickness of the oxide film and in particular on the relative hardness of the oxide and the metal substrate. When sliding occurs solely on the oxide layers the friction is not necessarily less than that observed when appreciable metallic contact occurs. The surface damage is, however, greatly diminished on account of the reduced metallic interaction.