Abstract: The poor corrosion resistance restricts the industrial applications of nanocrystalline soft magnetic Fe-Zr-B alloys. We reported a facile plasma-nitriding surface process to enhance the corrosion resistance of a nanocrystalline Fe₉₀Zr₇B₃ alloy without deteriorating its soft magnetic properties. Potentiodynamic polarization and electrochemical impedance spectroscopy were performed to investigate the corrosion behavior. The nitrided alloy shows higher corrosion resistance than the untreated alloy, as evidenced by a nobler corrosion potential, lower corrosion current and higher polarization resistance of surface corrosion film, while their magnetic properties are similar. The microstructures of both nanocrystalline alloys were examined by high-resolution transmission electron microscopy (HRTEM) and the compositions of their corrosion films analyzed by X-ray photoelectron spectroscopy (XPS). For the nitrided alloy, a more homogeneous nanocrystalline structure developed in the surface nitrided layer containing corrosion-resistant nitride phases (Fe₃N and ZrN) provides a higher resistance against chloride corrosion. Moreover, the nitrided layer facilitates the formation of a more protective corrosion film with the increased ratios of Fe²⁺/Fe³⁺ and O^2-/OH^- as well as higher enrichment of Zr- and B-oxides, while the N-species (NH₄⁺ and NO₃^-) formed in the corrosion film behave as good corrosion inhibitors and further enhance the film protection. Our findings provide a simple strategy for the preparation of corrosion-resistant nanocrystalline soft magnetic alloys to satisfy a variety of engineering requirements.

Key words: Plasma-nitriding, Nanocrystalline soft magnetic Fe-based alloys, Corrosion resistance, Corrosion film