HRTEM studies of grain boundaries in die-upset Nd-Fe-Co-Ga-B magnets

Highly textured magnets of MQU-F material (Nd13.6Fe73.6Ga0.6Co6.6B5.6) were produced by die-upsetting. A remanence B-r = 1.39 T, a coercivity mu(0j)H(c) = 1.18 T and an energy product (BH)(max) = 370 kJ m(-3) were obtained when using a relatively high degree of deformation (height reduction: 80%). Differential scanning calorimetry measurements reveal, beside an increase of the Curie temperature of the main phase, a substantial decrease of the melting point of the intergranular phase (660degreesC) in comparison to that of the ternary alloy MQP-A (680 degreesC). The microstructure of the hot-deformed MQU-F material, especially of the intergranular phase, was investigated by high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy (EDX) in the scanning transmission electron microscopic mode with a subnanometer probe. A very homogeneous distribution of the intergranular phase was observed. The Nd2Fe14B crystals are surrounded by an amorphous Nd-rich phase with a thickness of 0.4 to 2 nm. EDX analysis shows that the grain boundaries are enriched in Nd and Ga. Also, a small amount of Co was detected. (C) 2003 Elsevier B.V. All rights reserved.