Abstract
Magnetic properties and microstructure of high-energy (Nd,Dy)–Fe–B magnets with Dy of no more than 1 wt % prepared via a low-oxygen routine are studied. Oxygen content in magnets does not exceed 0.20 wt %. 0.5 wt %–Dy addition reliably stabilizes the coercivity MHc higher than 13 kOe; in this case, the maximum energy density product (BH)max of magnets is 48.5–49.5 MG Oe. High magnetic hysteresis properties are gained via optimization of chemical and phase compositions of magnets, as well as their microstructure. The grain size of the main Nd2Fe14B phase is approximately 3.5 μm; and according to X-ray analysis, the weight fraction of additional Nd-rich phases (NdOx and Nd2O3) does not exceed 2.5%. Scanning electron microscopy study has demonstrated that in triple junctions of Nd2Fe14B grains there are two types of inclusions (В and С) of the NdOx phase, which significantly differ by their chemical composition. С-phase inclusions with low oxygen content (х ≈ 0.03) are enriched in Fe (40–50 wt %); whereas, В-phase with high oxygen content (х ≈ 0.70) contains 3–5 times less Fe. The angular dependences of coercivity of (Nd,Dy)–Fe–B magnets are presented.
Highlights
Sintered Nd–Fe–B magnets are successfully applied in a wide range of efficient technical devices
Multiphase microstructure of sintered Nd–Fe–B magnets consists of the Nd2Fe14B grains, inclusions of phases localized at triple junctions of the Nd2Fe14B grains, and thin layers of the phase developed at the boundaries of grains
This article presents the study of magnetic hysteresis properties and microstructure of a wide range of highquality (Nd,Dy)–Fe–B magnets produced by Urals Electromechanical Plant, Joint-Stock Company via the low-oxygen routine
Summary
Sintered Nd–Fe–B magnets are successfully applied in a wide range of efficient technical devices. Researchers from Japan have studied in detail the chemical composition and structure of Ndrich phases [11, 12, 14,15,16,17] They have established that thin layers that separate the Nd2Fe14B grains have amorphous structure [9] and do not contain oxygen; they are ferromagnetic, because of their high Fe content [12, 19]. The Urals Electromechanical Plant, Joint-Stock Company implemented the low-oxygen technology, increasing (BH)max of sintered magnets up to 50 MG Oe [30]; the existing magnet production capacity can provide only 1 ton per year. This article presents the study of magnetic hysteresis properties and microstructure of a wide range of highquality (Nd,Dy)–Fe–B magnets produced by Urals Electromechanical Plant, Joint-Stock Company via the low-oxygen routine. X-ray diffraction was performed with a diffractometer Empyrean (PANanalytical) in CuKα irradiation
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