The friction and wear properties, during abrasion, of compressed graphite-powder compacts and commercial graphitised carbons

Abstract

The friction and wear properties during abrasion of compressed compacts made from ball-milled graphite powder are shown to vary systematically with the pressure of compaction. For abrasion on emery papers of particle diameter D > 70 rmmicrons the friction coefficient μ. is practically constant up to D = 150 microns or more, but the wear rate M still increases gradually with D. From the high wear volume rate in comparison with that for metals under similar conditions, and from the particulate nature of the wear debris, it is concluded that much of the wear occurs by brittle fracture; and this also accounts for the observed non-linear relation between M and μ. Some plastic flow by slip on (0001) planes also occurs. Both M and μ (at D > 70 microns) decrease with increase in the pressure of compaction of the graphite, and with the corresponding increase in the hardness of the compact. Some commercial samples which were well graphitised showed similar friction and wear properties, but in others a lower degree of graphitisation was associated with a lower particle size, higher hardness, and particularly low friction and wear. Theoretical considerations indicate that the adhesion component μa, of the total μ, is ~ 0.1, the remainder (0.2-0.5) being that due to the ploughing component μp.