AUTOLUBRICATION OF DIAMOND COATINGS AT HIGH SLIDING SPEED

We investigated the friction and wear properties of diamond coatings a t high sliding speed (V=30 m/s). Various types of diamond coatings wer e deposited on tungsten carbide pins. These coatings were produced by a combustion flame method under different deposition conditions. The s urface properties and morphology of the coatings have been characteris ed by surface analysis methods, such as scanning electron microscopy ( SEM) and Raman spectrometry (RS). The coated pins were tested by slidi ng against a rotating steel XC30 disc in ambient atmosphere. The hardn ess of the coated pin and the disc after heat treatment is 70 and 5 GP a, respectively. The experimental results show that at low sliding spe ed (V=1 m/s) the diamond coatings exhibit a very high friction coeffic ient of about 0.9-1.1. At high sliding speed (V=30 m/s) the friction c oefficient of these films decreases to 0.09-0.15, the wear of the diam ond films also decreases. This tribological behaviour of diamond coati ngs can be explained by the transformation of sp(3) to sp(2) carbon si tes on the rubbing surface during friction at high sliding speed. A mo del of the friction is proposed to explain this phenomenon. (C) 1998 E lsevier Science S.A. All rights reserved.