Tribological properties of carbon coatings produced by high temperature chlorination of silicon carbide

The tribological properties of highly disordered graphitic carbon layers fo rmed on silicon carbide (SiC) substrates by reaction with chlorine and chlo rine-hydrogen gas mixtures at 1000 degrees C were studied. Si was selective ly removed from the near surface of SiC by chlorine gas, leaving behind a l ayer of carbon having high structural density and strong bonding characteri stics. Tribological tests showed that the carbon films were highly adherent and able to reduce friction coefficients of the base SiC by factors of up to seven. There was little or no change in the frictional behavior of carbo n layers when sliding velocity and load were increased. Low friction coeffi cients (similar to 0.1) could be obtained under wet, dry,polished, and roug h conditions. The initially rough carbon surface underwent plastic flow pro ducing a smooth, self-adjusting carbon layer. Structural morphology and the amount of disorder in the carbon layers were correlated with the friction and wear performance of the resultant films.