Corrosion And Mechanical Properties Of Atomic Layer Deposited TiO2 Coatings On NiTi Alloys

Surface modifications of NiTi alloys for the purpose of improving their biocompatibility is of interest. In this study, TiO₂ layer is deposited on the surface of NiTi thin plates as a protection layer by using atomic layer deposition (ALD). The advantage of the ALD is an extremely conformal coating on 3D surface with a thickness control at atomic scale. During the ALD reaction, the temperature is kept at a value sufficient to prevent any unwanted structural changes in NiTi samples.

Various numbers of the ALD cycles are chosen to test the thickness effect on the corrosion resistance. The coated surface of NiTi is observed using scanning electron microscopy and vertical scanning interferometry before and after tensile mechanical loading. An attention is paid to some negative phenomena such as fracturing of the coated layers. The corrosion resistance of ALD thin films is studied using a potentiodynamic scan and impedance spectroscopy techniques in NaCl solution at 37^oC. We expect to see a positive effect of uniform and conformal passive barrier layers on the resistance against corrosion attack as we already observed with Al₂O₃ ALD coatings in our previous research.