On the polarisation and Mott-Schottky characteristics of an Fe-Mn-Al-Ni shape-memory alloy and pure Fe in NaCl-free and NaCl-contaminated Ca(OH)2,sat solution—A comparative study

Highlights: • The polarisation of Fe and a Fe-based shape memory alloy was analysed in Ca(OH)₂. • Simultaneously, the interfaces were observed and the influence of Cl⁻ was analysed. • The corrosion behaviour of the SMA is similar to iron under these conditions. • Mott-Schottky analysis revealed similar passive oxide properties before corrosion. • After polarisation the SMA passive oxide structure changes from n-type to n-/p-type. The polarisation behaviour of both the shape-memory alloy Fe-34Mn-17Al-5Ni and pure Fe were analysed in NaCl-free and NaCl-contaminated Ca(OH)_2,sat solutions. Simultaneously to the polarisation scan, corrosion progression at the interfaces was studied in-situ and correlated to the applied overpotentials. In NaCl-free Ca(OH)_2,sat, FeMnAlNi and Fe behave similarly, and are characterised by pronounced passivity at low overpotentials and intensive O₂ evolution at high overpotentials. In NaCl-contaminated Ca(OH)_2,sat, FeMnAlNi exhibits more severe pitting corrosion sensitivity than Fe. The pitting behaviour is rationalised based on the different semiconducting properties of the passive oxides, which were analysed by the Mott-Schottky technique.