Thermodynamics and heat treatment of B-enriched nanocomposite NdFeB alloys containing Dy

The thermodynamics of B-enriched NdFeB alloys (Nd1-xDyx)4.5Fe77B18.5 (x=0.0∼0.4) is investigated by the Kissinger method, with the aim of obtaining an optimized microstructure for these nanocomposite NdFeB alloys. The appearance activation energy (Ea) of the first two stages, calculated by the Kissinger method, increases with increasing Dy content. The crystallization procedure and microstructural evolution are characterized by differential scanning calorimetry (DSC), in-situ X-ray diffraction (XRD), and transmission electron microscopy (TEM). A step-annealing (SA) method is employed, and an optimal microstructure with a narrow distribution of grain sizes is obtained in the samples annealed by this method. Accordingly, the maximum remanence, remanence ratio, coercivity, and energy product of the samples annealed by the SA method are increased, from their values in conventionally annealed samples of the same compositions, to 1.30 T, 0.82, 261 kA/m, and 134 kJ/m3, respectively.