a-C(:H) and a-C(:H)_Zr coatings deposited on biomedical Ti-based substrates: Tribological properties

Amorphous carbon (a-C) based coatings are possible candidates as a surface treatment for various biocompatible materials used in medicine. In this study, the carbon coatings co-sputtered with Zr, deposited by dc unbalanced magnetron sputtering in Ar (non-hydrogenated, i.e. a-C/Zr) and Ar + CH4 (hydrogenated, i.e. a-C:H/Zr) discharges, were investigated and compared with pure carbon films. Polished pure commercial Ti grade 2 and Ti grade 5 ELI (Ti6Al4V) discs were used as substrates. To improve the coating/substrate adhesion, a gradient Ti-based interlayer was deposited (~ 450 nm). The coating structure was characterized by X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy; the chemical composition was measured by electron probe microanalysis. The adhesion was evaluated by scratch-test and the hardness was measured by nanoindentation. Tribological testing of the coatings was carried out using unidirectional pin-on-disc experiments; pure titanium balls were used as counterparts. The wear rate of the coatings was negligible except for the films with the highest Zr content deposited on Ti grade 2 substrates.

► The incorporation of Zr led to formation of nanocrystalline ZrC embedded into C-matrix.
► a-C:(H)-Zr coatings significantly improved the wear resistance of Ti-based alloys.
► Substrate plastic deformation led to lower coating adhesion on Ti grade 2.