In vitro electrochemical corrosion behavior of functionally graded diamond-like carbon coatings on biomedical Nitinol alloy

The anti-corrosion property plays an important role in determining the biocompatibility of metal implants. In this study, functionally graded diamond-like carbon coatings were deposited on the Nitinol substrate by hybrid magnetron sputtering and plasma enhanced chemical vapor deposition. A scratch test was adapted to study the adhesion strength of the coatings. The Si/SiC graded layer (up to 150 nm thick) provided good adhesion between the coating and the substrate, up to approximately 47.17 ± 2.1 N. The effectiveness of corrosion protection for the coated specimen was investigated in Tyrode's simulated body fluid. It was found that adhesion strength had a great influence on the effectiveness of corrosion protection, and the better adhesion strength, the better corrosion resistance. Compared to the others, the coating with a 150 nm thick Si/SiC graded layer provided better corrosion protection, and there existed no large amount of debonding and cracking of the coating around corrosion pits after the potentiodynamic polarization tests.