A graded nano-TiN coating on biomedical Ti alloy: Low friction coefficient, good bonding and biocompatibility

- A graded nano-TiN coating was prepared on biomedical Ti alloy by PVD.
- The combination of hard and soft phase increases hardness and toughness.
- The coating exhibits high bonding, low coefficient of friction and wear rate.
- The new coating has good bio-safety and great clinical application prospect.

In order to solve wear resistance of Ti alloy biomaterials, the concept of a graded nano-TiN coating has been proposed. The coating was prepared on Ti-6Al-4V bio-alloy by DC reactive magnetron sputtering. The wear performance of the coated specimens was measured in Hank's solution under the load of 10 N, and the biocompatibility was evaluated according to ISO-10993-4 standard. The results show that the gradient coating exhibits a gradual change in compositions and microstructures along the direction of film growth. Nano-TiN with the size of several to dozens nanometers and Ti4N3 − x transitional phase with variable composition form a graded composite structure, which significantly improves adhesion strength (Lc1 = 80 N, Lc2 = 120 N), hardness (21 GPa) and anti-wear performance (6.2 × 10− 7 mm3/Nm). The excellent bonding and wear resistance result from a good match of mechanical properties at substrate/coating interface and the strengthening and toughening effects of the nanocrystalline composite. The nano-TiN coating has also been proved to have good biocompatibility through in-vitro cytotoxicity, hemocompatibility and general toxicity tests. And thus, the proposed graded nano-TiN coating is a good candidate improving wear resistance of many implant medical devices.

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