Outstanding anti-corrosion performance in Nd-Fe-B permanent magnets by constructing a hydrophobic triplex surface coating

Anti-corrosion performance is a key factor that limits the lifetime of metallic components for diversified functional applications, particularly for the Nd-Fe-B permanent magnet in which vulnerable Nd is prone to rapid corrosion. To design corrosion-resistant Nd-Fe-B with a prolonged service life, we propose a facile strategy through a pre-coated water film and rapid air oxidation of 0.5-3 h to in situ grow a hydrophobic, thin and uniform surface coating on Nd-Fe-B. Advanced multi-scale techniques manifest that the triplex surface coating consists of an outermost layer of Fe2O3/Fe3O4, an intermediate layer of amorphous Nd2O3, an inner layer of amorphous Nd2O3 in a columnar alpha-Fe matrix. Among them, the nanometric Fe2O3 needles epitaxially grown on the outermost layer provide hydrophobic characteristics. The columnar alpha-Fe structurally coherent to the Nd2Fe14B matrix ensures a strong bonding and stable interface. All these benefits contribute to an outstanding anti-corrosion performance that endures even after 15 cycles of the Tafel test, accompanied by synergistic magnetic and mechanical performance. Prominently, rapid air oxidation for 0.5 h lowers the corrosion current by similar to 80% compared to pristine Nd-Fe-B. The above findings provide insights into designing corrosion-resistant metallic alloys in a scalable and robust fashion.