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

Abstract

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 α-Fe matrix. Among them, the nanometric Fe₂O₃ needles epitaxially grown on the outermost layer provide hydrophobic characteristics. The columnar α-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 ∼80% compared to pristine Nd–Fe–B. The above findings provide insights into designing corrosion-resistant metallic alloys in a scalable and robust fashion.