Monitoring tensile fatigue of superelastic NiTi Wire in liquids by electrochemical potential

0449564 - FZÚ 2016 RIV DE eng J - Journal Article
Racek, Jan - Stora, M. - Šittner, Petr - Heller, Luděk - Kopeček, Jaromír - Petrenec, M.
Monitoring tensile fatigue of superelastic NiTi Wire in liquids by electrochemical potential.
Shape Memory and Superelasticity. Roč. 1, č. 2 (2015), s. 204-230. ISSN 2199-384X. E-ISSN 2199-3858
R&D Projects: GA ČR GB14-36566G; GA ČR GA14-15264S; GA ČR GAP107/12/0800; GA MŠMT LO1409
Grant - others:FUNBIO(XE) CZ.2.16/3.1.00/21568
Institutional support: RVO:68378271
Keywords : nitinol * shape memory alloy * corrosion * fatigue * tensile test * electrochemistry * hydrogen embrittlement
Subject RIV: BM - Solid Matter Physics ; Magnetism

Fatigue of superelastic NiTi wires was investigated by cyclic tension in simulated biofluid. The state of the surface of the fatigued NiTi wire was monitored by following the evolution of the electrochemical open circuit potential (OCP) together with macroscopic stresses and strains. The ceramic TiO2 oxide layer on the NiTi wire surface cannot withstand the large transformation strain and fractures in the first cycle. Based on the analysis of the results of in situ OCP experiments and SEM observation of cracks, it is claimed that the cycled wire surface develops mechanochemical reactions at the NiTi/liquid interface leading to cumulative generation of hydrogen, uptake of the hydrogen by the NiTi matrix, local loss of the matrix strength, crack transfer into the NiTi matrix, accelerated crack growth, and ultimately to the brittle fracture of the wire.
Permanent Link: http://hdl.handle.net/11104/0251089