THE EFFECT OF BIOLOGICAL-FLUIDS ON THE ADHESION OF DIAMOND-LIKE CARBON-FILMS TO METALLIC SUBSTRATES

Diamond-like carbon (DLC) films deposited by standard r.f. glow discharge CVD were exposed to various fluids (distilled water, phosphate-buffered saline (PBS) solution and 40% serum in PBS) to study the effect of this exposure on the stability of DLC coatings on metallic substrates. A substrate plastic straining technique was used to study the strength and adhesion of the coatings before and after exposure to various fluids. Distilled water had no apparent effect, whereas PBS caused localized debonding and cracking of the film. The serum-PBS solution had an intermediate effect. X-Ray photoelectron spectroscopy (XPS) measurements indicated that PBS tends to penetrate through surface perforations and attack the thin transition layer of graded Si/C composition between the Si-rich layer on the substrate and the DLC coating. An increase in exposure temperature increased the population of defects in samples exposed to PBS. Coatings on Ti were found to be more resistant to damage.