The high entropy multi-component diffusion of Tb60Dy10Cu10Al10Zn10 effectively enhances the diffusion depth of heavy rare earths and coercivity in NdFeB magnets

Abstract

Grain boundary diffusion (GBD) magnets are essential for high-power density motors in applications like new energy vehicles and wind power. However, current GBD magnets face challenges such as limited diffusion depth and low heavy rare earth (HRE) utilization, hindering their development. In this study, magnetron sputtering was used to deposit 10 μm thick quinary Tb₆₀Dy₁₀Cu₁₀Al₁₀Zn₁₀, binary Tb₇₀Cu₃₀, and Tb diffusion layers on commercial 52H magnets. After diffusion heat treatment, GBD magnets were produced. Magnetic tests showed that coercivity increased from 16.72 kOe to 23.53kOe, 22.02 kOe, and 22.03 kOe for the quinary, binary, and Tb diffusion magnets, respectively. The quinary diffusion magnet achieved 22.23 kOe/wt% HRE, significantly higher than 16.85 kOe/wt% HRE and 14.67 kOe/wt% HRE for Tb₇₀Cu₃₀ and Tb diffusion magnets. Microstructural analysis revealed that, compared to binary TbCu and Tb diffusion magnets, the HRE-rich shell and thin grain boundary phase in the quinary diffusion magnet extended further along the diffusion direction, leading to high coercivity. Quantitative Tb analysis confirmed that quinary alloy diffusion enhances HRE diffusion depth. We propose that higher entropy in multi-component diffusion sources lowers Gibbs free energy, preventing HRE from entering main phase grains, thus improving diffusion depth and HRE utilization. Multi-component diffusion is a promising approach for high-performance GBD NdFeB magnets. Our study offers valuable insights for advancing GBD magnets.