Journal
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
Volume 477, Issue -, Pages 237-243Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jmmm.2019.01.062
Keywords
Nd-Fe-B permanent magnet; Grain boundary diffusion; Low melting-point alloy; Coercivity
Funding
- National Natural Science Foundation of China [51401021]
- Major Technologies R&D Program of Ningbo [2016B10007]
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Effect of Tb content and diffusion parameters (diffusion temperature and time) on boundary structure and magnetic properties of Nd-Fe-B sintered magnet was systematically studied by grain boundary diffusion process (GBDP) using Pr70-xTbxCu15Al15 (x = 5, 10, 15, 20, atom fraction) alloys. When x increases from 5 at% to 15 at %, coercivities of diffused magnets increase from the original 11.9 kOe to 22.4 kOe for 5 at% magnet (PTCA-5) and 23.5 kOe for 15 at% magnet (PTCA-15), with a slight decrease in remanence. With x increasing to 20 at% (PTCA-20), coercivity of diffused magnet is only 0.6 kOe higher than that of PTCA-15 magnet, with sharp decrease in remanence. So, Tb content in Pr-Tb-Cu-Al alloy should be limited. And when diffusion temperature and time increase from 600 degrees C and 2 h to 950 degrees C and 8 h, coercivities of diffused magnet linearly increase first, and then reach stable. The enhancement mechanisms for magnetic properties contribute to magnetic hardening by Tb-rich shells, magnetic isolation by continuous Nd-rich grain boundary phases and reduced lattice misfit between Nd-rich phases and Nd2Fe14B grains. Furthermore, distribution of Tb-rich shells along diffusion length can be optimized by adjusting Tb content in diffusion sources and diffusion parameters, contributing to coercivity enhancement of magnet.
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