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In the part I of this study, friction tests were conducted using both pin-on-disk and disk-on-disk setups. Despite the nature of the friction scales, similar results were found. In the friction of carbon materials, it has been found that the coefficient of friction is dependent on the total energy absorbed by a given mass and the rate of the energy dissipation. We observed that at high energy conditions, the occurrence of friction transition does not appear related to moisture effects. In this part of the study, the friction of the study, the friction surface wasexamined using various macro and nanoscopic techniques to understand the evolution of friction film before, during and after friction transition. Examination of the friction surfaces display two distinct surface characteristics: shiny and dull bands. Structural changes of friction film have been observed from graphitic allotropic form to amorphous type structure. This sudden change leads to an increase of the coefficient of friction. It seems that the inter-laminar shearing and disruption of the film might cause the friction transition. In this paper, friction behavior of a graphitic carbon at high energy had been studied. At high power input, hot spots had been generated. The current study shows that both the friction transition and hot spots had occurred because of friction film break-off and powdered slits had formed. The presence of these particles surface contributes in the increase of the coefficient of friction (μ>1) and its instabilities. more...

In the friction of carbon materials, it has been found that the coefficient of friction is dependent on the total energy absorbed by a given mass and the rate at which the energy is dissipated. Usually, low energy absorption and low rate of energy dissipation produces relatively high coefficients of friction. Conversely, high energy absorption and high rate of energy dissipation leads to lower coefficients of friction. In addition, testing at low energy input in a moist environment produces a low coefficient of friction, which may increase significantly during the course of the test. Similar friction transitions occur during high energy tests. However, these do not appear related to moisture effects. In some higher velocity tests, very high local temperatures were detected even though the bulk temperature rise is relatively low. The scope of this paper focuses on the transient changes of friction coefficient and the hot spotting phenomena. The tests were conducted using both pin-on-disk and disk-on-disk setups. Although test scales were different in both tests, a very good match in results was found. more...