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-assis ted glow discharge CVD on AISI 304 stainless steel and Ti-6Al-4V subst rates. A substrate plastic straining technique (to measure the strengt h and adhesion of the coating) and erosion testing (to measure its dur ability) have been used, before and after exposure to various fluids ( distilled water, phosphate buffered saline solution (PBS) and bovine s erum). The films on both substrates had excellent adhesion before expo sure to the fluid, being slightly higher for those on Ti substrates. P BS solution affected the adhesion adversely, whereas distilled water a nd serum had no apparent effect. Fourier transform infrared (FTIR) and Raman spectroscopic studies revealed that there were no changes in th e atomic structure of the coatings during exposure. X-ray photoelectro n spectroscopy (XPS) measurements indicated that PBS tends to penetrat e through perforations in the film and attack the thin transition laye r of graded Si/C com position between the a: Si-H layer and the DLC co ating. An increase in exposure temperature increased the population of defects in samples exposed to PBS. Coatings on Ti exhibited similar c haracteristics, but were considerably more resistant to damage. This m ay be due to a lower incidence of defects and perforations in these fi lms.