Biotribological performance of NCD coated Si3N4–bioglass composites

A nanocrystalline diamond (NCD) coated Si3N4–bioglass composite, with potential use for hip and knee joint implants, was tribologically tested in simulated physiological fluids. NCD was deposited using a hot-filament chemical vapour deposition (HFCVD) apparatus in an Ar–H2–CH4 gas mixture. Self-mated reciprocating experiments were performed using a pin-on-flat geometry in Hanks' balanced salt solution (HBSS) and dilute fetal bovine serum (FBS). A nominal contact pressure of 25 MPa was applied for up to 500,000 cycles. Very low friction coefficients of 0.01–0.02 were measured using HBSS, while for FBS lubricated tests the values are slightly higher (0.06–0.09), due to a protein attaching effect. AFM assessed wear rates by an approach using the bearing function for volume loss quantification, yielding wear rates of k ∼ 10− 10 mm3 N− 1 m− 1 in HBSS and k ∼ 10− 9–10− 8 mm3 N− 1 m− 1 for FBS, characteristic of very mild wear regimes.