Abstract
Nanocrystalline soft magnetic materials with low coercivity, high saturation magnetization and high permeability are commonly used as cores in transformers and generators in stress and field sensors. The influence of factors connected with corrosion is almost impossible to eliminate. In the present work, a comparative study of the electrochemical behavior of Fe 78Si 13B 9 and Fe 73.5Si 13.5B 9Nb 3Cu 1 amorphous and nanocrystallized alloys, tested in 0.5 M NaCl solution, has been performed by linear polarization and electrochemical impedance spectroscopy methods. Changes of magnetic properties including coercivity, induction and magnetic retentivity were analyzed. These properties were investigated as a function of the structure of primary amorphous ribbons and as a function of corrosion environment type, in which longitudinally and transversely cut ribbon specimens were exposed for 15 days. The best magnetic properties were found for the Fe 78Si 9B 13 ribbon after a structural relaxation at a temperature of 350 °C for an hour and for the Fe 73.5Si 13.5B 9Nb 3Cu 1 ribbon after a primary crystallization at a temperature of 550 °C for an hour. Corrosion did not cause the direct degradation of the magnetic properties of the Fe 78Si 9B 13 and Fe 73.5Si 13.5B 9Nb 3Cu 1 alloys. The corrosion processes occurring on the surface of the Fe 73.5Si 13.5B 9Nb 3Cu 1 alloy ribbon with the amorphous structures improve induction B s. Most probably it is connected with the decrease of undesirable stresses blocking a motion of magnetic domain walls on the ribbon surface. Changes of corrosion mechanism depending on structure and applied solution were analyzed. The electrochemical impedance experiment were performed at open circuit potential for amorphous and nanocrystalline specimens. Two electrochemical corrosion mechanisms of Fe 73.5Si 13.5B 9Nb 3Cu 1 alloy in 0.5 M NaCl solution were found. Charge transfer control mechanism is typical for amorphous (as received) alloys. Mixed mechanism-mass transport and charge transfer controlled was observed for nanocrystalline Fe 73.5Si 13.5B 9Nb 3Cu 1 alloy.
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