Presentation Information
[P1-14]Effects of trace elements on the grain boundary diffusion of sintered NdFeB magnets
*Chaochao Zeng1, Jiayi He1, Xichun Zhong1, Hongya Yu1, Zhongwu Liu1 (1. School of Materials Science and Engineering, South China University Of Technology (China))
Keywords:
Sintered Nd-Fe-B magnet,Trace elements,Grain boundary diffusion,Coercivity
In response to the substantial increase in demand for high-performance rare earth permanent magnets, cost-effective grain boundary diffusion technology has become an important technology for preparing Nd-Fe-B based magnets with high coercivity. Generally, there are various unintentionally added trace elements in NdFeB magnets such as O, H, N, and C. To improve the performance of the magnets, a small amount of Ga, Zr, or Nb may also be doped in the magnets. Until now, the effects of these trace elements on the grain boundary diffusion of NdFeB magnets have not been well understood.
In this work, grain boundary diffusion was carried out on the sintered Nd-Fe-B magnets containing different contents of O, C, and Nb. Tb-Cu alloy was employed as the diffusion source. The influences of these three elements on the microstructure and magnetic properties of the diffused magnets were investigated. Fig.1 shows the coercivity enhancement (ΔHcj) and Tb concentrations against diffusion depth from the surface of the diffused magnets with different levels of O, C, and Nb contents. Fig.1a shows that the ΔHcj decreases from 683 kA/m to 513 kA/m with the increase of O content from 320 ppm to 460 ppm in the magnets. Fig.1b shows that the increase in C content also decreases the diffusion efficiency. As C content increased from 550 ppm to 1200 ppm, the ΔHcj decreases from 664 kA/m to 297 kA/m. Similarly, the increase of niobium from 0.5 wt.% to 1 wt.% also decreases the ΔHcj of diffused magnets from 1174 kA/m to 920 kA/m, as shown in Fig.1c. The microstructure analysis was carried out to understand the effect mechanism of the trace elements. The results indicated that the increased O and C content leads to more high melting point oxides in the magnet, which impedes the Tb diffusion and reduces the diffusion efficiency of Tb. For the effect of Nb, more high melting point Nb-rich phases presented in the magnets with high Nb content also impedes the Tb diffusion. As shown in Fig1, the weight percentages of Tb content inside the diffused magnets with higher O (Fig.1d), C (Fig.1e) and Nd (Fig.1f) contents are lower than those in the magnets with lower O, C, Nb content, respectively. The results indicated that the high melt-point intermetallic compound presented in the grain boundary is not beneficial to the grain boundary diffusion. More detailed investigations on the microstructure of the studied magnets have also been carried out to verified above results. This work is important for the optimization of sintered Nd-Fe-B magnets for efficient grain boundary diffusion.
In this work, grain boundary diffusion was carried out on the sintered Nd-Fe-B magnets containing different contents of O, C, and Nb. Tb-Cu alloy was employed as the diffusion source. The influences of these three elements on the microstructure and magnetic properties of the diffused magnets were investigated. Fig.1 shows the coercivity enhancement (ΔHcj) and Tb concentrations against diffusion depth from the surface of the diffused magnets with different levels of O, C, and Nb contents. Fig.1a shows that the ΔHcj decreases from 683 kA/m to 513 kA/m with the increase of O content from 320 ppm to 460 ppm in the magnets. Fig.1b shows that the increase in C content also decreases the diffusion efficiency. As C content increased from 550 ppm to 1200 ppm, the ΔHcj decreases from 664 kA/m to 297 kA/m. Similarly, the increase of niobium from 0.5 wt.% to 1 wt.% also decreases the ΔHcj of diffused magnets from 1174 kA/m to 920 kA/m, as shown in Fig.1c. The microstructure analysis was carried out to understand the effect mechanism of the trace elements. The results indicated that the increased O and C content leads to more high melting point oxides in the magnet, which impedes the Tb diffusion and reduces the diffusion efficiency of Tb. For the effect of Nb, more high melting point Nb-rich phases presented in the magnets with high Nb content also impedes the Tb diffusion. As shown in Fig1, the weight percentages of Tb content inside the diffused magnets with higher O (Fig.1d), C (Fig.1e) and Nd (Fig.1f) contents are lower than those in the magnets with lower O, C, Nb content, respectively. The results indicated that the high melt-point intermetallic compound presented in the grain boundary is not beneficial to the grain boundary diffusion. More detailed investigations on the microstructure of the studied magnets have also been carried out to verified above results. This work is important for the optimization of sintered Nd-Fe-B magnets for efficient grain boundary diffusion.
