Novel mechanism of the grain boundary diffusion process with Tb based on the discovery of TbFe2 phase

doi:10.1016/j.jmst.2024.05.081

Abstract

Abstract: The grain boundary diffusion process (GBDP) has proven to be an effective method for enhancing the coercivity of sintered Nd-Fe-B magnets. However, the limited diffusion depth and thicker shell structure have impeded the further development of magnetic properties. Currently, the primary debates regarding the mechanism of GBDP with Tb revolve around the dissolution-solidification mechanism and the atomic substitution mechanism. To clarify this mechanism, the microstructure evolution of sintered Nd-Fe-B magnets during the heating process of GBDP has been systematically studied by quenching at different temperatures. In this study, it was found that the formation of TbFe₂ phase is related to the dissolution of Nd₂Fe₁₄B grains during GBDP with Tb. The theory of mixing heat and phase separation further confirms that the Nd₂Fe₁₄B phase dissolves to form a mixed phase of Nd and TbFe₂, which then solidifies into the (Nd, Tb)₂Fe₁₄B phase. Based on the discovery of the TbFe₂ phase, the dissolution-solidification mechanism is considered the primary mechanism for GBDP. This is supported by the elemental content of the two typical core-shell structures observed.

Key words: Grain boundary diffusion process, TbFe₂ phase, Dissolution-solidification mechanism, Core-shell structure, The theory of mixing heat and phase separation

Wendi Zhang, Zilong Wang, Xiaojun Sun, Weibin Cui, Haijun Peng, Wenlong Yan, Yang Luo, Dunbo Yu. Novel mechanism of the grain boundary diffusion process with Tb based on the discovery of TbFe₂ phase[J]. J. Mater. Sci. Technol., 2025, 214: 120-129.

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Novel mechanism of the grain boundary diffusion process with Tb based on the discovery of TbFe₂ phase

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