Microstructure and magnetic properties developed by hot pressing of cast Pr–Fe–B magnets

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Abstract
The hot pressing process of cast Pr19Fe74.5B5Cu1.5 magnets were studied. Microstructure studies reveal that during the hot pressing, the crushing of Pr2Fe14B matrix grains and the relative slip and rotation between the grains take place and the Pr-rich melt is squeezed out of the magnet, leading to fine, dense and well-aligned Pr2Fe14B grains surrounded by a thin Pr-rich phase layer in the fully-deformed magnets. Magnetic properties of Br=9.9 kG, iHc=11.0 kOe and (BH)max=24.0 MG Oe are obtained. The increase of coercivity is attributed to the fine Pr2Fe14B grains and the thin Pr-rich phase layer continuously distributed at the grain boundaries. The increasing remanence results primarily from the development of the easy-axis alignment as well as from the densification of the Pr2Fe14B matrix. The easy-axis alignment is developed by the relative slip and rotation of the crushed Pr2Fe14B grains. A full and slow hot pressing is necessary for developing a good easy-axis alignment and high magnetic properties.

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