Effect of cobalt addition on the corrosion behavior of near equiatomic NiTi shape memory alloy in normal saline solution: electrochemical and XPS studies

Nawal D Alqarni; Joanna Wysocka; Nader El-Bagoury; Jacek Ryl; Mohammed A Amin; Rabah Boukherroub

doi:10.1039/c8ra02031k

Effect of cobalt addition on the corrosion behavior of near equiatomic NiTi shape memory alloy in normal saline solution: electrochemical and XPS studies

RSC Adv. 2018 May 24;8(34):19289-19300. doi: 10.1039/c8ra02031k. eCollection 2018 May 22.

Authors

Nawal D Alqarni¹, Joanna Wysocka², Nader El-Bagoury^{1

3}, Jacek Ryl², Mohammed A Amin^{1

4}, Rabah Boukherroub⁵

Affiliations

¹ Materials Science and Engineering Group, Department of Chemistry, Faculty of Science, Taif University 888 Hawiya Saudi Arabia maaismail@yahoo.com.
² Department of Electrochemistry, Corrosion and Materials Engineering, Chemical Faculty, Gdansk University of Technology Narutowicza 11/12 80-233 Gdansk Poland.
³ Central Metallurgical Research and Development Institute (CMRDI) P. O. Box: 87 Helwan Cairo Egypt.
⁴ Department of Chemistry, Faculty of Science, Ain Shams University 11566 Abbassia Cairo Egypt.
⁵ Univ. Lille, CNRS, Centrale Lille, ISEN, Univ. Valenciennes UMR 8520 - IEMN F-59000 Lille France.

Abstract

The electrochemical and corrosion (uniform and localized) behavior of a binary Ni₅₂Ti₄₈ shape memory alloy (SMA) and two ternary Ni₅₂Ti_48-x Co _x (x = 1.5 and 4.0 wt%) SMAs were studied. Measurements were conducted in 0.9% NaCl solution at 37 °C employing various electrochemical methods. These include: linear polarization resistance (LPR), linear sweep voltammetry (LSV), chronoamperometry and dynamic electrochemical impedance spectroscopy (DEIS). Such measurements were complemented with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. Results revealed that the addition of alloyed Co to NiTi significantly reduced the uniform corrosion rate of the studied SMA and greatly enhanced its pitting corrosion resistance. XPS measurements evidenced high stability of the passive layer and limited adsorption of chloride ions. Additionally, it was found that the passive layer remained primarily composed of titanium oxides. Microstructure changes accompanying the addition of Co were also used to account for its role in improving the corrosion resistance of these materials.