Nickel titanium (NiTi) shape memory alloys (SMAs) are well known for their significant shape recovery under thermomechanical loading [1]. Austenitic SMA can recover its original shape upon unloading (pseudoelasticity) while martensitic SMA can do so after subsequent heating (shape memory effect). Understanding the corrosion behavior of NiTi SMAs is important for extending their successful applications. Studying the corrosion of SMAs is challenging due to the inherent complexity of their constitutive response together with the presence of different phases (austenite or martensite) and microstructural states (twinned or detwinned) [2].

In this study, the corrosion behavior of equiatomic NiTi under quasi-static loading in the plastic deformation regime is studied in artificial physiological solution at room temperature. Elelctrochemcial Frequencies Modulation (EFM) technique is used the parameters of which has been found in a previous study by the authors [3]. The corrosion parameters of NiTi are measured at different load levels during plastic deformation where the passive breakdown occurs. Strain distribution on the surface of the plastically deforming NiTi sample corresponding to these load levels is captured by means of Digital Image Correlation (DIC) technique [4]. Metal loss is measured using Faraday’s law and Open Circuit Potential (OCP) measurements show that the repassivation of oxide layer is not taken place. The findings are considered a step towards better understanding of the corrosion behavior of SMAs under thermo-mechanical loading.

References

[1] Lagoudas, D.C. ed., 2008. Shape memory alloys: modeling and engineering applications. Springer Science & Business Media.

[2] Mohajeri, M., Haghgouyan, B., Castaneda, H. and Lagoudas, D.C., 2018. Nickel Titanium Alloy failure analysis under thermal cycling and mechanical Loading: A Preliminary Study. arXiv preprint arXiv:1803.01110.

[3] Mohajeri, M., Castaneda, H. and Lagoudas, D.C., 2018, March. Corrosion monitoring of NiTi alloy with small-amplitude potential intermodulation technique. In Behavior and Mechanics of Multifunctional Materials and Composites XII (Vol. 10596, p. 1059616). International Society for Optics and Photonics.

[4] Haghgouyan, B., Shafaghi, N., Aydıner, C.C. and Anlas, G., 2016. Experimental and computational investigation of the effect of phase transformation on fracture parameters of an SMA. Smart Materials and Structures, 25(7), p.075010.