EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

During the last few years high entropy alloys (HEAs) have drawn a lot of attention mainly due to the vast range of designed compositions and properties. For many potential applications good corrosion resistance is among the principal requirements. In spite of numerous publications covering this topic, much information is still missing about the influence of individual components on the corrosion behaviour of HEAs. One of important components is molybdenum, which is known to supress the pitting corrosion of stainless steels, but its effect on HEAs is not obvious. In this work, a nanostructured medium-entropy alloy, AlCrFe2Ni2, with excellent mechanical properties and resistance to corrosion in NaCl solutions was modified with molybdenum to investigate the electrochemical behaviour in an acidic solution, 0.1M H2SO4. The experimental alloys had a general formula AlCrFe2Ni2Mox (x = 0.00, 0.10, 0.15, 0.32 and 0.64).
The evaluation was based on immersion tests, potentiodynamic polarization tests, time-dependence of current density and electrochemical impedance spectroscopy. After exposure the samples were characterised by scanning electron microscopy and different X-ray techniques. Thin foils were analysed by transmission electron microscopy and electron diffraction. Regardless of the Mo content, all alloys showed passivation in a wide range of potential, i.e. enhanced corrosion resistance resulting from the formation of protective films. Immersion test at 50⁰C allowed identification of an amorphous layer of MoOx on alloys modified with molybdenum. As the data on phase composition, chemical composition, microstructure and formation mechanism of the Fe/Cr/Mo-containing passive films on alloy surface are still very limited in the literature, the results of systematic studies presented in this work will contribute to better understanding of the relevant processes.
Acknowledgements.
The work being part of M-ERA.NET2 NADEA project has been financially supported by the National Science Centre in Poland, UMO-2017/26/Z/ST8/01238. Experimental alloys have been produced by ACCESS e.V. Aachen, Germany.