Morphological control of diamond thin films: its influence on friction and wear

Microwave plasma enhanced chemical vapor deposition was used to grow diamond films with different morphologies and surface roughnesses. With the proper choice of deposition parameters (111) faceted, octahedral, flat (100) and microcrystalline diamond films were obtained. Scanning electron microscopy, atomic force microscopy and stylus profilometry were used to assess the surface topography for each type of film. Raman spectroscopy and x-ray diffraction were also used to determine the purity of the diamond phase and growth orientation of the films, respectively. Single pass friction and wear tests were conducted on each film in order to determine the effect of surface morphology on the coefficient of friction and wear of the counterface materials and/or diamond films. Counterface materials included alumina, tungsten carbide, zirconia, and the (100) face of a synthetic diamond single crystal. Results showed a decrease in the coefficient of friction as the film roughness decreased. Specific wear of the non-diamond counterface materials showed a marked decrease for the flatter and smoother diamond surfaces. For diamond on diamond, the coefficient of friction also decreased as film topography became smoother. Wear of the diamond films occurred by fracture or shearing of asperity tips which was most severe for the rougher films. Control of diamond morphology is shown to be of paramount importance in tribological applications in order to reduce abrasive wear, material transfer, and diamond film fracturing.