NANOINDENTATION AND NANOWEAR TESTS ON AMORPHOUS-CARBON FILMS

To clarify the physical and tribological properties of pure amorphous carbon films, nanoindentation and scanning-scratched wear tests were c onducted on pure amorphous carbon films, diamond and graphite, by usin g an atomic force microscope with a diamond tip. Two types of pure amo rphous carbon films (amorphous carbon 1 and amorphous carbon 2) were d eposited on silicon substrates. To evaluate the tribological character istics of the surface layers of the films, the thickness of the films was set at about 50nm to eliminate the substrate effect. Deposition wa s performed by electron cyclotron resonance plasma sputtering. The int ernal stress of amorphous carbon film was compressive and it was about 0.4 GPa for the amorphous carbon films and 1.4 GPa for the amorphous carbon 2 films. Raman spectra of the amorphous carbon films showed an amorphous graphite-like structure. Auger electron spectroscopy, second ary-ion mass spectroscopy and Rutherford back-scattering spectroscopy showed that the deposited films contained argon and several atomic per centage of hydrogen. Nanoindentation tests showed that the order of ha rdness was diamond > amorphous carbon 2 > amorphous carbon I much grea ter than graphite. The ratio of the residual indentation depth at 20 m u N was about 1:3:6 for amorphous carbon 2:amorphous carbon I:graphite (the residual indentation depth of diamond was zero). Scanning-scratc hed wear tests (2 cycles) showed that the wear of diamond and amorphou s carbon 2 was shallow and that of amorphous carbon 1 was several time s deeper than that of amorphous carbon 2. The order of wear resistance was diamond > amorphous carbon 2 > amorphous carbon 1 much greater th an graphite. The ratio of the wear depth at 40-80 mu N loads was about 1:2:5 for diamond:amorphous carbon 2:amorphous carbon 1. The wear of graphite was extremely deep. Scanning-scratched wear tests (repeated c ycles) showed that amorphous carbon 2 was more wear resistant than amo rphous carbon 1. The wear depth of amorphous carbon 1 at a load over 5 mu N increased as the number of scanning-scratch cycles increased, bu t the wear at 1 mu N remained very shallow within 50 cycles. On the ot her hand, the wear of amorphous carbon 2 at loads below 10 mu N remain ed very shallow within 50 cycles, but the wear depth at 20 mu N increa sed with increasing number of cycles. There was an explicit correlatio n between the indentation hardness and the wear resistance for the amo rphous carbon films. Furthermore, we presume that hard and wear-resist ant characteristics of the amorphous carbon films resulted from random ly assembled graphite cluster structures.