Friction and adhesion behavior of polycrystalline diamond films deposited on metals

Polycrystalline diamond films with different grain sizes and thickness are coated on copper with a titanium interlayer. Friction and wear behavior of the coatings against steel is tested using a block-on-ring tribotester. Raman spectroscopy is used to characterize the diamond quality and to access residual stress in the coatings being tested under different wear loads. More non-diamond phases are found in thinner film, which still exhibits high wear resistance as evidenced by scanning electron microscopy. It is shown that the friction coefficient is proportional to the diamond grain size and the wear load. After the wear tests, the diamond coatings still adhere to the substrate. However, Raman spectra show a smaller shift in the diamond peak than that before the test; this may imply an actual decreasing in the coating adhesion, or it could relate to graphitization in the wear test.