Influence of Nitride Coatings on Corrosion Resistance and the Biocompatibility of Titanium Alloy Products

The bioadhesion of bacteria to the surface of samples with Ti–TiN, Zr–ZrN, Zr–(Zr, Nb)N, and Zr–(Zr, Hf)N coatings was studied via incubation with gram-positive strains of Staphylococcus aureus. The samples were kept at 25 °C for 30 days in a 3% NaCl solution. The deposition of coatings slows, whereas oxidation processes intensify. The oxygen content on the TiN and (Zr, Nb)N coating surfaces was higher than that of the Ti sample without a coating. Samples with ZrN and, especially, (Zr, Hf)N coatings resist oxidation better. Regarding bioactivity toward S. aureus, the highest density of biological forms was observed on the surfaces of TiN and (Zr, Hf)N coatings. The lowest density was on the surfaces of uncoated, ZrN-coated, and (Zr, Nb)N-coated samples. On Ti–TiN, Zr–ZrN, and Zr–(Zr, Nb)N coatings, the formation of surface biostructures of a filamentary type was observed. In the uncoated sample, the biostructures have an island character, and in the sample with a Zr–(Zr, Hf)N coating, the formation of extensive areas of biostructures was observed. Between the biostructures and coating, a layer 5 to 15 nm thick was observed, presumably associated with bacterial adhesion. The presence of biostructures on the coating surface can activate or slow oxidation processes.