Microstructural characterization, wettability and cytocompatibility of gradient coatings synthesized by gas nitriding of three-layer Ti/Ni/Ti nanolaminates magnetron sputtered on the TiNi substrate

In the study, gradient coatings with a nanometer thickness were successfully synthesized from Ti/Ni/Ti nanolaminates on the TiNi substrate in a nitrogen atmosphere at 900 °C. A technique for producing a gradient coating includes magnetron sputtering of Ti/Ni/Ti nanolayers with a total thickness of 75 nm and 150 nm on a TiNi substrate and further synthesis of the coating by annealing the sample in a nitrogen atmosphere. The developed technique allows to form stable phases of titanium nitride and intermetallic oxynitrides, which are a reliable barrier to nickel diffusion from the substrate to the surface. No nickel was found on the surface of the synthesized coatings. In the synthesized coating from 150 nm thick nanolaminate, these barriers are Ti4Ni2(N,O) and TiN phases. In the synthesized coating from 75 nm thick nanolaminate, these barriers are two continuous TiN layers. The cytocompatibility of the coating synthesized from Ti/Ni/Ti nanolaminates with a total thickness of 150 nm was positively affected by a mixed-phase composition of titanium nitrides and oxides, moderate roughness and hydrophilicity