Carbon nitride films on orthopedic substrates

The mechanical and tribological properties of carbon nitride (CN X ) films deposited on orthopedic substrates are presented. CN X films were prepared by d.c. reactive magnetron sputtering from a graphite target in N 2/Ar plasma. Films were grown on Ni and ZrO 2 substrates to a thickness of ∼1 μm at a total pressure of 3 mtorr and a substrate temperature of 250°C. High-resolution transmission electron microscopy (HRTEM) shows dense and homogeneous films, with ‘fullerene-like’ microstructures consisting of curved, frequently intersecting, and highly in-plane oriented basal lattice planes. Nanoindentation measurements revealed a change in the mechanical properties of films treated with three different biological solutions. Spectroscopic analysis confirmed a change in the chemical structure of the treated films. The friction coefficients of CN X films against high speed steel (HSS), ZrO 2 and Ultra-High Molecular Weight Polyethylene (UHMWPE) balls were evaluated by ball-on-disk tests in dry and lubricated conditions. In the case 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 the ZrO 2 substrate. The friction coefficients under human serum lubrication conditions were below 0.18 for the ZrO 2 and UHMWPE balls. An increase in wettability of human plasma on CN X films was observed compared to the orthopedic surfaces, which could enhance the retention of synovial fluid on those surfaces, improving the lubrication of the bearings of total joint arthroplasty components during function.