Effect of heat treatment on corrosion properties of CuAlNi shape memory alloy
(1. Department of Electrochemistry and Materials Protection, Faculty of Chemistry and Technology, University of Split, Ru？era Bo？kovi？a 35, 21000 Split, Croatia;
2. Faculty of Metallurgy, University of Zagreb, Aleja narodnih heroja 3, 44103 Sisak, Croatia;
3. Faculty of Natural Sciences and Engineering, University of Ljubljana, A？ker？eva cesta 12, 1000 Ljubljana, Slovenia)
2. Faculty of Metallurgy, University of Zagreb, Aleja narodnih heroja 3, 44103 Sisak, Croatia;
3. Faculty of Natural Sciences and Engineering, University of Ljubljana, A？ker？eva cesta 12, 1000 Ljubljana, Slovenia)
Abstract: The effect of heat treatment on corrosion properties of CuAlNi shape memory alloy was investigated in 0.9% NaCl solution at pH 7.4 and 37 °C by open circuit potential measurements, polarisation techniques, and electrochemical impedance spectroscopy. Investigations were performed on CuAlNi alloy samples in as-cast state and after heat treatment procedure containing annealing at 850, 885 and 920 °C followed by water quenching. Electrochemical impedance measurement results indicate that heat treatment of CuAlNi alloy leads to the increase in charge transfer resistance and surface layer resistance and the decrease in values of capacitance of the double and surface layers, indicating higher corrosion resistance compared with the as-cast CuAlNi alloy. The increase in polarisation resistance and the decrease in corrosion current density of heat-treated CuAlNi alloy also suggest beneficial influence of heat treatment on corrosion resistance of CuAlNi alloy. Optical microscopy, SEM/EDX and XRD analysis of samples surface after polarisation measurements show the occurrence of pitting corrosion on the electrode surfaces, with the existence of CuCl2, AlCl3 and Cu2Cl(OH)3 compounds as the surface corrosion products.
Key words: CuAlNi alloy; corrosion; polarisation; electrochemical methods; SEM