Microstructural, Electrochemical, Mechanical, and Biocompatibility Characterization of ReN Thin Films Synthesized by DC Sputtering on Ti6Al4V Substrates

Thin films of ReN were synthesized by DC sputtering at different nitrogen pressures (120, 140, 160, and 180 mTorr) on silicon and Ti6Al4V substrates. The coatings were evaluated for their microstructural and mechanical properties. Additionally, the biocompatibility and electrochemical properties of the films were studied using Hanks’ lactate solution at 37 °C. X-ray diffraction (XRD) confirmed the formation of cubic ReN with higher nitrogen content. The optimized nitrogen pressure (180 mTorr) allowed the complete formation of the cubic phase of ReN. Regarding electrochemical behavior, ReN coatings significantly improve corrosion resistance, reducing the corrosion rate as nitrogen content increases, reaching 0.0145 µm/year at 180 mTorr. Regarding mechanical properties, the deposited ReN films presented an optimal combination of hardness and elastic modulus for the highest nitrogen contents. Cell viability was assessed by comparing uncoated and coated samples using a live/dead staining assay, demonstrating the biocompatibility of the coatings. To complement this study, scanning electron microscopy (SEM) was used to analyze the protein–coating interaction and cell morphology on the surface of the samples.