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. Ram an spectroscopy is used to characterize the diamond quality and to access r esidual stress in the coatings being tested under different wear loads. Mor e non-diamond phases are found in thinner film, which still exhibits high w ear resistance as evidenced by scanning electron microscopy. It is shown th at the friction coefficient is proportional to the diamond grain size and t he wear load. After the wear tests, the diamond coatings still adhere to th e substrate. However, Raman spectra show a smaller shift in the diamond pea k than that before the test: this may imply an actual decreasing in the coa ting adhesion, or it could relate to graphitization in the wear test. (C) 2 000 Elsevier Science S.A. All rights reserved.