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) tech nique onto metallic substrates (304 steel and Ti-6A1-4V), has been mea sured by a novel method in which the coating is bombarded with small s olid particles in a carefully controlled manner. Two different types o f particle, soft rounded glass beads and hard angular silica particles , were used to examine the effect of particle type on the wear behavio ur. The durability was measured both before and after exposure of the specimens to various biological fluids, including distilled water, pho sphate-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 experi ments was carried out at 60 degrees C to determine the effect of tempe rature on the film stability. Environmental exposure had little direct effect on the film properties, but the fluids tended to degrade the i nterfacial adhesion when penetration to the interface was possible. Th is can occur via microscopic penetrations in the film or via the edges . The buffered saline solution appeared to be the most aggressive in t his respect. A correlation between the damage mechanism during solid p article erosion and the type of particle used was found.