3D optical-profilometric assessment of transfer and its significance for the mechanisms of primary particle detachment and wear

3D profilometry technique was used to systematically assess the 2D and 3D characteristics of discontinuous 3rd bodies as a function of rubbing cycles n and various parameters. The model system chosen consists of a pin of graphite rubbing in repeated sliding and controlled environment against thoroughly polished steel. At room temperature and during a relatively extended initial phase, the whole amount of material detached from Ist body was shown to remain in the contact where it builds up discrete transfer particles. Thus, the 3D assessment of the kinetics of transfer volume growth dV/dn is also relevant for the rate of elementary particle detachment. A systematic study of the variations of dV/dn as a function of sliding speed v revealed that they are of the form: alog v + b, where a and b are further strongly influenced by relative humidity, the material's stiffness, and the nature of graphite. These results reveal that similarly to the friction force, the mechanism of particle detachment may also be controlled by stick-slip phenomena. A new model of stick-slip including the possibility of a cohesive rupture was shown to qualitatively account for most of the experimental results. (C) 1999 Elsevier Science S.A. All rights reserved.