The effect of biological fluids on the response of DLC films to a novel erosion durability test

The durability of diamond-like carbon (DLC) films, deposited by an r.f. plasma-assisted glow discharge chemical vapour deposition (CVD) technique onto metallic substrates (304 steel and Ti-6A1-4V), has been measured by a novel method in which the coating is bombarded with small solid particles in a carefully controlled manner. Two different types of particle, soft rounded glass beads and hard angular silica particles, were used to examine the effect of particle type on the wear behaviour. The durability was measured both before and after exposure of the specimens to various biological fluids, including distilled water, phosphate-buffered saline (PBS) solution and 40% bovine serum in sterile PBS. The specimens were exposed for 7 and 28 days at 37 degrees C in a humidified atmosphere containing 5% carbon dioxide. One set of experiments was carried out at 60 degrees C to determine the effect of temperature on the film stability. Environmental exposure had little direct effect on the film properties, but the fluids tended to degrade the interfacial adhesion when penetration to the interface was possible. This can occur via microscopic penetrations in the film or via the edges. The buffered saline solution appeared to be the most aggressive in this respect. A correlation between the damage mechanism during solid particle erosion and the type of particle used was found.