NANOSCALE INDENTATION HARDNESS AND WEAR CHARACTERIZATION OF HYDROGENATED CARBON THIN-FILMS

An experimental investigation of tire surface topography nanoindentati on hardness, and nanowear characteristics of carbon thin films was con ducted using atomic force and point contact microscopy. Hydrogenated c arbon films of thickness 5, 10, and 25 nm were synthesized wing a sput tering technique. Atomic force microscopy images obtained with silicon nitride tips of nominal radius less than 20 nm demonstrated that the carbon films possessed very similar surface topographies and root-mean -square roughness values in the range of 0.7-1.1 nm. Nanoindentation a nd nanowear experiments performed with diamond tips of radius equal to about 20 nm revealed a significant enhancement of the hardness and we ar resistance,vith increasing film thickness. High-resolution surface imaging indicated that plastic flow was the dominant deformation proce ss in the nanoindentation Experiments. Tile carbon wear behavior was s trongly influenced by variations in the film thickness, normal lend, a nd number of scanning cycles. For a given film thickness, increasing t he load caused the transition from an atomic-scale wear process, chara cterized by asperity deformation and fracture, to severe wear consisti ng of plowing and cutting of the carbon films. Both the critical load and scanning time for severe wear increased with film thickness. Below the critical lend, the wear rate decreased with further scanning and tire amount of material Mom off was negligibly small, while above the critical load the wear rate increased significantly resulting in the r apid removal of carbon. The observed behavior and trends are in good q ualitative agreement with the results of other experimental and contac t mechanics studies.