Carbon nitride films on orthopedic substrates

The mechanical and tribological properties of carbon nitride (CNX) films de posited on orthopedic substrates are presented. CNX films were prepared by d.c. reactive magnetron sputtering from a graphite target in N-2/Ar plasma. Films were grown on Ni and ZrO2 substrates to a thickness of similar to1 m um at a total pressure of 3 mtorr and a substrate temperature of 250 degree sC. High-resolution transmission electron microscopy (HRTEM) shows dense an d homogeneous films, with 'fullerene-like' microstructures consisting of cu rved, frequently intersecting, and highly in-plane oriented basal lattice p lanes. Nanoindentation measurements revealed a change in the mechanical pro perties of films treated with three different biological solutions. Spectro scopic analysis confirmed a change in the chemical structure of the treated films. The friction coefficients of CNX films against high speed steel (HS S), ZrO2 and Ultra-High Molecular Weight Polyethylene (UHMWPE) balls were e valuated by ball-on-disk tests in dry and lubricated conditions. In the cas e of dry sliding against a HSS ball, the steady state friction coefficient values are 0.22 for the film on the Ti substrate and 0.26 for the film on t he ZrO2 substrate. The friction coefficients under human serum lubrication conditions were below 0.18 for the ZrO2 and UHMWPE balls. An increase in we ttability of human plasma on CNX films was observed compared to the orthope dic surfaces, which could enhance the retention of synovial fluid on those surfaces, improving the lubrication of the bearings of total joint arthropl asty components during function. (C) 2000 Elsevier Science B.V. All rights reserved.