Magnetics Hysteresis Properties and Microstructure of High-Energy (Nd,Dy)–Fe–B Magnets with Low Oxygen Content

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 M H c 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 Nd 2 Fe 14 B phase is approximately 3.5 μm; and according to X-ray analysis, the weight fraction of additional Nd-rich phases (NdO x and Nd 2 O 3 ) does not exceed 2.5%. Scanning electron microscopy study has demonstrated that in triple junctions of Nd 2 Fe 14 B grains there are two types of inclusions (В and С) of the NdO x 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.