Influence of diamond characteristics on the tribological behaviour of metals against diamond-coated Ti-6Al-4V alloy

The tribological behaviour in ambient air of the 100Cr6 steel and the Ti-6A l-4V alloy sliding against various diamond coatings deposited at 600 degree sC on Ti-6Al-4V by microwave plasma is reported. It has been studied as a f unction of the diamond coating type on a rotating pin-on-disk tribometer. A s-deposited rough polycrystalline, polished polycrystalline and as-deposite d smooth fine-grained diamond coatings were tested. They were characterised by their surface roughness and their diamond quality defined as the relati ve amounts of sp(3)- and sp(2)-hybridised carbons incorporated in the coati ng. The strong influence of the diamond surface roughness has been evidence d whatever the counterface alloy. The counterface materials present, howeve r, different tribological behaviours either against rough polycrystalline d iamond coatings or fine-grained ones. These behaviours also depend on the d iamond quality. Different friction and wear mechanisms are discussed as a f unction of these parameters. The advantages of fine-grained diamond coating s with respect to polycrystalline coatings are emphasised. Very low wear ra tes of the alloys and low friction coefficients, in the 0.05-0.1 range, wer e obtained for the smoothest coatings, even under heavy load. The great adh esion of the coatings has been deduced from the absence of coating failure, crack and stress relaxation in the disk track. (C) 2001 Elsevier Science B .V. All rights reserved.