Tribological mechanism of hydrogenated amorphous carbon film against pairs: A physical description

The objective of the present study was to investigate the friction and wear mechanisms of hydrogenated amorphous carbon (a-C:H) films sliding against different counterparts. Friction tests were performed by a reciprocating ball-on-disk tribometer with an applied load of 5 N, amplitude of 5 mm, and frequency of 5 Hz, in ambient air at room temperature. The coefficient of friction (COF) was consistent with the varied tendency of the contact area of the counterparts on films and also coincided with the varied tendency of the coverage of transfer film on friction ball surface. It was important to point out that the coverage of the transfer film on the counterpart surface was inversely proportional to the contact area. Furthermore, COF of a-C:H films against different pairs was independent with the film graphitization level. Additionally, wear rate of a-C:H films against different friction pairs was discussed in details. Some indexes including hardness ratio of pair and film, elastic energy density of the friction pair, and effective plastic index were employed to predicting the wear behavior of the a-C:H films sliding against different counterparts. Compared with other indexes, the effective plastic index showed best performance. Description of physical meanings and some formula derivation of the effective plastic index of film with applied load were also performed in this work. The results increased our understanding of the physical mechanism of a-C:H films sliding against pairs, which were able to guide the application of a-C:H films in the future industrial fields.