EVIDENCE OF GRAPHITIZATION OF DIAMOND-LIKE CARBON-FILMS DURING SLIDING WEAR

Diamond-like carbon (DLC) exhibits excellent wear and friction charact eristics. Transmission electron microscopy (TEM) has been used to inve stigate the substructures of as-deposited DLC and DLC debris after wea r testing. The as-deposited DLC was found to consist of a dense, three -dimensional network structure with a medium range order (< 3 nm) pres ent. Diffraction pattern analysis showed that DLC was mainly amorphous . Two diffuse diffraction rings with d(111) = 0.21 nm and d(220) = 0.1 2 nm were observed, suggesting the presence of a short-range cubic dia mond structure (sp(3)). Morphologically, the wear debris was found to be a discontinuous segregation of carbon particles ranging from nano- to micro-size. Diffraction pattern analysis showed that the debris con sisted of graphite (sp(2)) and distorted DLC (sp(3)). A wear mechanism has been proposed based on the transformation of DLC to graphite. The transformation is related to the frictional energy and includes two s tages: hydrogen release from the structure causing lattice relaxation and shear deformation of the DLC structure producing graphite.