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

• Published in: Journal of alloys and compounds Vol. 365; no. 1; pp. 286 - 290
• Main Authors: Kirchner, A., Thomas, J., Gutfleisch, O., Hinz, D., Müller, K.-H., Schultz, L.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 25.02.2004; Elsevier
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Magnetic properties and materials; Materials science; Metals. Metallurgy; Microstructure; Permanent magnets; Physics; Rare earth compounds; Studies of specific magnetic materials; TEM; Transition metal compounds; Treatment of materials and its effects on microstructure and properties; Permanent magnets; Transition metal compounds; Rare earth compounds; Microstructure; TEM; Grain boundaries; Differential scanning calorimetry; Forming processes; Scanning electron microscopy; Curie point; Experimental study; Texture; Materials preparation; Transmission electron microscopy; Rare earth alloys; Transition element alloys; Iron base alloys
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/S0925-8388(03)00661-3

Highly textured magnets of MQU-F material (Nd 13.6Fe 73.6Ga 0.6Co 6.6B 5.6) were produced by die-upsetting. A remanence B r=1.39 T, a coercivity μ 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 (660 °C) in comparison to that of the ternary alloy MQP-A (680 °C). 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 Nd 2Fe 14B 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.