Environmental fatigue of superelastic NiTi wire with two surface finishes

0534041 - ÚJF 2021 RIV NL eng J - Journal Article
Racek, J. - Šittner, Petr
Environmental fatigue of superelastic NiTi wire with two surface finishes.
Journal of the Mechanical Behavior of Biomedical Materials. Roč. 111, NOV (2020), č. článku 104028. ISSN 1751-6161. E-ISSN 1878-0180
R&D Projects: GA MŠMT EF16_013/0001794
Institutional support: RVO:61389005
Keywords : Nitinol * Shape memory alloy * Martensitic transformation * Surface damage * Electrochemical corrosion tests * Environmental fatigue tests
OECD category: Condensed matter physics (including formerly solid state physics, supercond.)
Impact factor: 3.902, year: 2020
Method of publishing: Limited access
https://doi.org/10.1016/j.jmbbm.2020.104028

Surface finish of NiTi is widely perceived to affect its biocompatibility and corrosion fatigue performance. The aim of this work was to find out, whether a carefully engineered surface oxide shows any beneficial effect over electropolished surface on the fatigue performance of superelastic NiTi wire mechanically cycled in simulated biofluid. Series of corrosion and environmental fatigue tensile tests was performed on superelastic NiTi wire with two different surface finishes frequently used in medical device industry. Open Circuit Potential reflecting the activity of chemical reactions on the surface of the wire cycled in electrochemical cell was continuously monitored during the fatigue tests. Microcracks at the surface of the fatigued NiTi wires were characterized by SEM and TEM. It was found that the carefully engineered 70 nm thick TiO2 oxide provides the NiTi wire with similar level of protection against the static corrosion as the less than 10 nm thin natural oxide on the electropolished wire and that it does not have any positive effect on its performance in environmental fatigue tests, whatsoever. On the contrary, the wire covered by the carefully engineered 70 nm thick TiO2 oxide displayed systematically poorer fatigue performance upon tensile cycling under specific critical loading conditions (strain amplitude <0.5% at large mean strains 1-7%).
Permanent Link: http://hdl.handle.net/11104/0312253