Structural, mechanical, corrosion, and early biological assessment of tantalum nitride coatings deposited by reactive HiTUS

Abstract

This study examined microstructure, mechanical, corrosion properties and initial biological evaluation of the tantalum nitride (Ta-xN, where x – nitrogen flow rate during deposition) coatings prepared by reactive High Utilization Sputtering (HiTUS) at various nitrogen flow rates (x = 0, 2, 4, 6, and 8 sccm). Coatings were deposited on a novel Mg alloy (Mgbal.-Zn0.9-Y2.05-Al0.25 at. %) containing long-period stacking ordered (LPSO) phases. The coatings' structure was analyzed using a combination of SEM/FIB/TEM techniques, while XRD determined the phase composition. The mechanical parameters investigated included hardness, indentation modulus, and scratch behavior. The corrosion resistance of the coatings with respect to the bare substrate was evaluated in chloride-containing solutions. The wettability and early biological assessment of the coatings were also examined. The phase evolution strongly influenced the hardness and indentation modulus. The Ta-xN coatings made at x = 2 sccm nitrogen corresponding to HCP-Ta2N exhibited the highest hardness and indentation modulus. An increase in nitrogen flow rates resulted in the formation of FCC structure with slightly reduced hardness and indentation modulus. In addition, Ta-xN coatings (x ≥ 4sccm) showed superior corrosion resistance compared to BCC structured α-Ta, enhancing the corrosion performance of the Mg-LPSO bulk substrate. Finally, at the early incubation stage (24 h), L929 fibroblasts exhibited better cell attachment to the Ta-6N coating than to the bare Mg-LPSO substrate.