Tribological performance of diamond-coated Ti-6Al-4V alloy with respect todiamond characteristics

Polycrystalline and smooth fine-grained diamond coatings with different cha racteristics were deposited on Ti-6Al-4V at 600 degrees C in a microwave pl asma. Surface roughness of as-deposited polycrystalline and fine-grained di amond coatings was in the 15-140 nm (r.m,s,) range. Some polycrystalline co atings were polished after deposition to a final roughness of 5 nm. Sliding experiments were conducted in ambient air with a rotating pin-on-disk trib ometer. The friction coefficient of uncoated Ti-6Al-4V pins during sliding against the two types of diamond coatings was in the 0.05-0.1 range after a run-in period. The fine-grained diamond coatings provided low friction coe fficients and low wear rates to the titanium counterbodies, All the results showed the great influence of the surface roughness and the influence of t he diamond quality on the tribological results. Sliding tests between two d iamond-coated counterfaces evidenced a self-polishing mechanism leading to ultra smooth wear tracks and a low final wear rate. The advantages of the f ine-grained diamond coatings with respect to the polycrystalline coatings w ere also pointed out in that case. The great adhesion of the coatings was d educed from the absence of coating failure, crack and stress relaxation in the disk track even at high load. (C) 2000 Elsevier Science S.A. All rights reserved.