Effect of deposition temperature and target-substrate distance on the structure, phases, mechanical and tribological properties of multi-layer HA-Ag coatings obtained by RF magnetron sputtering

Abstract The effect of variation in the process parameters of target-substrate distance (4 cm, 6 cm and 8 cm) and deposition temperature between room temperature (RT) and 200 °C, on the chemical composition, structure, phases, mechanical and tribological properties of multi-layer hydroxyapatite (HA) – silver coatings deposited by magnetron sputtering was evaluated. Characterization of the films obtained was performed by energy dispersive spectroscopy, micro-Raman spectroscopy, X-ray diffraction, optical microscopy, atomic force microscopy, scanning electron microscopy, nanoindentation and tribological testing. Better control of the chemical composition and phases was found for coatings deposited at 200 °C, with a Ca/P ratio of 1.66 recorded for the system obtained at 4 cm distance from the target. Moreover, the vibration of the OH− group of HA was preferentially observed in coatings deposited at this temperature. Similarly, higher crystallinity was evidenced in comparison to the coatings obtained at room temperature. Similar behaviors were found for the mechanical properties, which for each system, reduced with increased distance, and improved with increased temperature. Again, the highest values were obtained for the coating deposited at 4 cm and 200 °C, which presented hardness of 7 ± 0.4 GPa, elastic modulus of 134 ± 7 GPa, and critical load of 169 ± 5 mN. Conversely, slightly higher friction coefficients and slightly lower wear rates were obtained in the coatings deposited at 200 °C in comparison to those deposited at RT. Delamination was the predominant wear mechanism in the coatings obtained.