Mechanical and tribological characterization of diamond-like carbons coatings on orthopedic materials

Diamond-like carbon (DLC) coatings prepared using the filtered cathodic vacuum arc (FCVA) technique have excellent mechanical and tribological properties over other techniques. Hence, an investigation has been carried out to study the influence of substrate and substrate bias voltage (in the preparation of the soft layer) on the properties of multi-layer DLC films that were prepared on three different orthopedic metallic substrates [Ti, Ti-6Al-4V and stainless steel (316L)]. The morphology, microstructure, mechanical and tribological characterizations of the films were investigated using atomic force microscopy, Raman spectroscopy, XPS surface analysis, a nano-indenter and a pin-on-disk tribometer. The Raman spectroscopy results show a decreasing sp³ fraction (an increasing trend in I_D/I_G ratio) with increasing bias voltage, irrespective of the difference in the substrates being used, and the hardness results confirm the decreasing sp³ content with increasing bias voltage. The long-run tribological characterization against sapphire friction partner shows that the coefficients of friction of the samples do not differ much; however, the failure of the DLC film on titanium alloy is quite obvious. The differences in failure are believed to be due to the adhesion of DLC coating on to the respective metal substrates.