Corrosion resistance, mechanical properties and biocompatibility of Hf-containing ZrCN coatings

The aim of this work was to study the properties of Hf containing ZrCN protective layers in term of corrosion resistance, tribological and biocompatible properties, in order to improve the performance and service life of the orthopedic systems. The coatings were prepared by the DC magnetron sputtering technique in a mixture of Ar, N2 and CH4 gases, and analyzed for elemental composition and chemical bonds, crystalline structure, mechanical properties, surface morphology, electrochemical corrosion resistance and tribological performance in Ringer solution, being also evaluated for biocompatibility by in vitro tests. Two overstoichiometric film compositions, with non-metal/metal ratios of about 2.0 and 3.5, respectively, were obtained by varying the total gas (CH4 + N2) flow rate, while maintaining constant the CH4/N2 flow ratio. The coatings characteristics were assessed in comparison to ZrCN reference coatings. The coatings were found to mainly consist of a mixture of crystalline metal carbonitride and free carbon phases. The coatings exhibited a pure fcc solid solution, with (111) preferred orientation and crystallite size in the range 8–16 nm. The hardness values increased at Hf addition with 5.1–5.3 GPa, while critical loads between 42 and 54 N were measured at adhesion scratch test. Better corrosion resistance and tribological characteristics were obtained by incorporating Hf into the basic ZrCN fcc structure. The deposited coatings exhibited good biocompatibility characteristics during in vitro tests, whatever the non-metal/metal ratio. The highest cell viability was found for the ZrHfCN coatings with the highest (~ 3.5) non-metal/metal ratio.

► Overstoichiometric ZrHfCN protective coatings for biomedical applications
► Coatings with different film compositions were produced by magnetron sputtering.
► Hf addition in basic ZrCN structure improved the film characteristics.