THE EFFECT OF EXPOSURE TO BIOLOGICAL-FLUIDS ON THE SPALLATION RESISTANCE OF DIAMOND-LIKE CARBON COATINGS ON METALLIC SUBSTRATES

Diamond-like carbon (DLC) films have been deposited by RF plasma-assisted glow discharge CVD on AISI 304 stainless steel and Ti-6Al-4V substrates. A substrate plastic straining technique (to measure the strength and adhesion of the coating) and erosion testing (to measure its durability) have been used, before and after exposure to various fluids (distilled water, phosphate buffered saline solution (PBS) and bovine serum). The films on both substrates had excellent adhesion before exposure to the fluid, being slightly higher for those on Ti substrates. PBS solution affected the adhesion adversely, whereas distilled water and serum had no apparent effect. Fourier transform infrared (FTIR) and Raman spectroscopic studies revealed that there were no changes in the atomic structure of the coatings during exposure. X-ray photoelectron spectroscopy (XPS) measurements indicated that PBS tends to penetrate through perforations in the film and attack the thin transition layer of graded Si/C com position between the a: Si-H layer and the DLC coating. An increase in exposure temperature increased the population of defects in samples exposed to PBS. Coatings on Ti exhibited similar characteristics, but were considerably more resistant to damage. This may be due to a lower incidence of defects and perforations in these films.