An Investigation of the Mechanism of the Friction and Wear of Carbon

Abstract

A comparison has been made of the friction and wear characteristics of carbons of high (p = 0.1) and low (p = 0.9) graphiticity (hereafter referred to as graphitic and nongraphitic) in vacuo, air, and CO2 at ambient room temperature. The friction of nongraphitic carbon can be just as low as graphitic carbon and it is similarly affected by absorbed gases. It is different, however, in that it periodically exhibits a substantial increase of friction which is not normally observed with graphitic carbon. The surface orientation produced by rubbing is also quite different and so is the mode of wear. These differences have been investigated and are explained in terms of the different physical properties associated with the structures of the two materials. On the basis of this work a critical assessment has been made of the various theories concerning the mechanism of the friction of graphitic carbon. The results are in accord with the view that the low friction of graphitic carbon (and of nongraphitic carbon) is due to low adhesion between crystallites, not to the low shear strength nor to the separation of the surfaces by rolled up crystallites.