The corrosion behaviour of Fe–15Mn–7Si–9Cr–5Ni shape memory alloy

Abstract The corrosion behaviour of Fe–15Mn–7Si–9Cr–5Ni (mass%) shape memory alloy at 25 °C in 0.5 M H 2 SO 4 and 3.5% NaCl solutions has been studied using potentiodynamic polarization and electrochemical impedance techniques. Three different microstructures viz., single-phase γ, γ-δ and γ-Fe 5 Ni 3 Si 2 , were produced by heat-treating the alloy in different equilibrium phase fields. The corrosion behaviour in 0.5 M H 2 SO 4 solution is almost same for all three microstructures, barring a slight difference in the passivation range. Although, the passivation current in 0.5 M H 2 SO 4 , is in the same range as that of SS 304, the critical current required for onset of passivation is almost three orders higher and the passivation range is much shorter. In 3.5% NaCl solution the corrosion behaviour of all three microstructures of the Fe–15Mn–7Si–9Cr–5Ni shape memory alloy was that of general dissolution without passivity or localized attack (pitting). The best corrosion resistance in both H 2 SO 4 and NaCl solutions is shown by the single-phase γ microstructure.