Micro-friction of Graphite

Abstract

SOLIDS with a layer-like structure have long been materials of interest in frictional studies. In general they are found to possess a low coefficient of friction and have often been used as dry lubricant films. We have recently studied the friction of graphite at very small loads (∼ 1 to 400 mg). The experiments were carried out in a scanning electron microscope so that surface deformation (to a resolution of about 500 A) could be observed as it occurred during sliding. In this way it was possible to study directly the marked difference in sliding behaviour for sliding on the basal and on the edge planes. The slider was generally a tungsten stylus, tip radius about 1 µm and was loaded on to the other, flat, surface using a delicate galvanometer movement. (A similar device used in micro-hardness studies has been described by Gane1.) The flat specimen could be traversed under the stylus thus keeping the stylus within the field of view of the microscope. The specimen stage was carried on a stiff double spring and the frictional force was determined by measuring, with a differential capacitance device, the deflexion of the spring. The sensitivity of the friction measurements was 0.05 mg and the sliding speed was 0.7 µm s−1.