Electrochemical corrosion and its influence on magnetic properties of Fe75.5Si13.5B9Nb3Cu1 alloy

Nanocrystalline soft magnetic materials with low coercivity, high saturation magnetization and high permeability are commonly used as cores in transformers and generators, stress and field sensors in a technological application. The influence of factors connected with a corrosion is almost impossible to eliminate. From this reason the investigations in the direction of knowledge of an electrochemical corrosion mechanism and its influence on magnetic properties of Fe73.5Si13.5B9Nb3Cu1 alloy were performed. In the present work, a comparative study of the electrochemical behaviour of Fe73.5Si13.5B9Nb3Cu1 amorphous, amorphous relaxed and nanocrystallized alloy tested in 0.5 M Na2SO4 solution, has been performed by means of electrochemical technique: direct current technique (anodic polarization) and alternating current technique (electrochemical impedance spectroscopy). Regardless of structure, the multicomponent alloy Fe73.5Si13.5B9Nb3Cu1 had an ability to passivation in the sulphate solution. Data concerning a corrosion mechanism obtained by the use of electrochemical impedance spectroscopy method (alternating current technique). Dependent on the structure of investigated alloys tested in 0.5 M Na2SO4 solution at the temperature of 20 °C, two electrochemical corrosion mechanisms were distinguished: electron transfer control and mixed electron transfer and mass transport rate control. On the basis of obtained impedance spectra, the equivalent circuit models describing electrochemical corrosion processes of the amorphous, amorphous relaxed and nanocrystalline Fe73.5Si13.5B9Nb3Cu1 alloy and interpretation of equivalent circuit elements was presented. Changes of magnetic properties including coercivity, magnetization were analyzed. These properties were investigated as a function of the produced structure in primary amorphous ribbon and exposure specimens for 15 days in corrosive environment.