TRIBOLOGICAL PERFORMANCE OF DIAMOND AND DIAMOND-LIKE CARBON-FILMS AT ELEVATED-TEMPERATURES

In this study, the authors investigated the tribological performance o f diamond and diamondlike carbon (DLC) films as a function, of tempera ture. Both films were deposited on silicon carbide (SiC) by microwave plasma chemical vapor deposition and ion-beam deposition processes. Tr ibological tests were performed on a reciprocating wear machine in ope n air (20 to 30% relative humidity) and under a 10 N load using SiC pi ns. For the test conditions explored, the steady-state friction coeffi cients of test pairs without a diamond ol DLC film were 0.7 to 0.9 and the average wear rates of pins were 10(-5) to 10(-7) mm(3)/N-m, depen ding on, ambient temperature. DLC films reduced the steady-state frict ion coefficients of the test pairs by factors of three three to five a nd the wear rates of pins by two to three orders of magnitude. Low fri ction coefficients were also obtained with the diamond films, but wear rates of the counterface pins were high due to the very abrasive natu re of these films. The wear of SiC disks coaled with either diamond or DLC films was virtually unmeasurable while the wear of uncoated disks was substantial. Test results showed that the DLC films could afford low friction up to about 300 degrees C. At higher temperatures, the DL C films graphitized and were removed from the surface. The diamond fil ms could withstand much higher temperatures, but their tribological be havior degraded. Raman spectroscopy and scanning electron microscopy w ere used to elucidate the friction. and wear mechanisms of both films at high temperatures.