Nanocrystalline Diamond Coated SiC Balls in Tribometer

Abstract

Nanocrystalline diamond(NCD) coated SiC balls were applied in a ball-on-disk tribometer. After seeding in an ultrasonic bath containing nanometer diamond powders, 2.2 µm thick NCD films were deposited on sintered 3 mm diameter SiC balls at 600 o C in a 2.45 GHz microwave plasma CVD system. Bare ZrO 2 and SiC balls were prepared for comparison as test balls. Tribology tests were performed in air with pairs of three different balls and mirror polished steel(SKH51) disk. The wear tracks on balls and disks were examined by optical microscope and alpha step profiler. Under the load of 3 N, the friction coefficients of steel against ZrO 2 , SiC and NCD-coated balls were between 0.4 and 0.8. After a few thousands sliding laps, the friction coefficient of NCD-coated balls dropped from 0.45 to below 0.1 and maintained thereafter. Under a higher load of 10 N or 20 N with a long sliding distance of 2 km, ZrO 2 and SiC balls exhibited the similar friction coefficients as above. The friction coefficient of NCD-coated balls was less than 0.1 from the beginning and increased to above 0.1 steadily or with some fluctuations as sliding distance increased. NCD coating layers were found worn out after long duration and/or high load sliding test, which resulted in the friction coefficient higher than 0.1.