CHARACTERIZATION OF WEAR SURFACES IN DRY SLIDING OF STEEL AND ALUMINAON HYDROGENATED AND HYDROGEN-FREE CARBON-FILMS

Hydrogenated amorphous carbon coatings were deposited by r.f. plasma a nd hydrogen-free carbon films in pulsed arc discharge on stainless ste el substrates. The coatings were characterized and evaluated in tribol ogical tests. Pin-on-disc tests were used over a wide range of test pa rameters: normal load, 5-40 N; sliding velocity, 0.1-3.0 m s-1. The we ar of both coatings was of the same order of magnitude (0.7 x 10(-3)-5 .1 x 10(-3) mm3). However, the wear of the counterface was one order o f magnitude higher for the hydrogen-free carbon coatings. Increasing t he normal load generally caused an increase in coating wear and in mos t cases also an increase in counterface wear. When the steel pin was s liding against the hydrogenated carbon coating with a high sliding vel ocity and load, a rather thick tribofilm was formed on the pin wear su rface, lowering the coefficient of friction and reducing the pin wear. The tribofilm formed on the alumina pin sliding against the hydrogena ted carbon film also seemed to reduce the friction coefficient but cou ld not prevent the pin wear. A tribofilm was also formed on the pin we ar surface when the hydrogen-free carbon coating was sliding against t he steel and alumina pins, but the layer was not able to protect the p ins. The tribofilm did, however, lower the coefficient of friction, wh ich was rather insensitive to the different test parameters used. Acco rding to secondary ion mass spectroscopy analyses, material transfer o f the pin was detected on the disc (coated) wear surfaces. The tribofi lms formed on the pin wear surfaces consisted of pin material, hydroge n, oxygen, and carbon.