MECHANICAL AND TRIBOLOGICAL PROPERTIES OF AMORPHOUS-CARBON FILMS

The mechanical and tribological properties of amorphous carbon films h ave been studied in more detail in recent years because these films (a ) can be deposited near room temperature, thus allowing film depositio n on common engineering alloys (i.e., aluminum and steel) without alte ring their mechanical properties, and (b) are smooth and conform to su rface roughness of the substrate, thus requiring no post deposition pr ocessing. In addition, amorphous carbon films exhibit low unlubricated sliding friction in contact with steel and ceramics which is comparab le to that of steel against steel in a lubricated contact. The wear re sistance of these films is also better than Ti-based hard coatings. Fu rther improvement in film tribological properties can be achieved by m odifying film chemical composition. Because of these attractive featur es, amorphous carbon films have been evaluated in several applications including automotive, electronic and biomedical engineering. However, environmental factors such as oxygen and humidity have been found to influence tribological properties significantly. This paper reviews th e current understanding of the tribological properties of both hydroge nated and nonhydrogenated amorphous carbon films, the mechanisms respo nsible for low friction coefficient and identifies areas that require further research.