Abstract: Compared with the widely used industrial production process of sintering, hot deformation (HD) process has many advantages and it was once considered as a candidate technology for the fourth generation rare earth permanent magnets. At present, the research of HD Nd-Fe-B magnets mainly focuses on the magnet preparation and microstructure control[1]. One-step HD can shorten the preparation process of bulk anisotropic magnets to the minimum, which highlights the advantages of simple high-definition process. However, there are still many aspects of this method that have not been systematically studied in depth. In this study, the effects of deformation ratio and temperature on the microstructure and properties of NdFeB magnets were studied by adjusting the one-step HD process. The results show that the optimized magnetic properties with Hcj, Jr and (BH)max of 960 kA/m, 1.2 T and 33 MGOe are obtained at 750 oC with 80% deformation ratio, which are very close to the performance of ordinary hot pressing/hot deformation (HP/HD) magnets, as shown in Fig. 1 (a). The microstructure and corrosion resistance were studied. The results show that with the increase of HD temperature and deformation rate, the corrosion resistance of the magnet first increases and then decreases, and the platelet grains become more obvious. When the HD temperature exceeds 750 oC and the deformation exceeds 80%, the grain growth is too large and the grain boundary thickness decreases sharply. After 90%, there is no grain boundary phase and the grain shape of the two deformed magnets is basically the same, as shown in Fig. 1 (b). It can be considered that one-step HD can replace HP/HD and achieve the simplest process while maintaining the performance [2]. As shown in Figs. 1 (c) (d), with the increase of deformation rate and HD temperature, the magnetic energy product and remanence first increase and then decrease, and the coercivity monotonously decreases.

![](https://assets.underline.io/uploads/markdown_image/1/image/619f224750bb04aa175f6fb5c5df58c9.jpg)

Effects of deformation ratio and temperature on microstructure and properties of NdFeB magnets by one-step hot deformation

Abstract Grain boundary diffusion (GBD) provides a promising way for Nd-Fe-B magnets to obtain high coercivity with less consumption of critical rare earths (RE). With the expansion of application field, the mechanical and anti-corrosion properties of Nd-Fe-B magnets has attracted increasing attention except their magnetic properties. Here, we proposed a strategy to simultaneously enhance these properties by GBD without employing heavy rare earths (HRE). The diffusion sources of Pr70Al20Cu10 (PrAlCu) and Al75Cu25 (AlCu) were prepared by arc melting. The thickness of initial magnet is 4.5 mm. The results show that the coercivity can be enhanced from 1000 to 1346 and 1089 kA/m by diffusion of PrAlCu and AlCu, respectively (Fig. 1(a)). Interestingly, the compression strength of the magnets also increased by 485 and 252 MPa, respectively. In addition, it is found that AlCu diffusion can improve the corrosion resistance of the magnets, which is different from that of PrAlCu [1]. The microstructure analysis showed that PrAlCu diffusion leads to the formation of continuous grain boundary (GB) layers for magnetic decoupling and strong binding between 2:14:1 grains (Fig. 1(b)). Although the non-RE diffusion source of AlCu shows less efficiency in increasing the content of RE-rich GB phases (Fig. 1(c)), it reduces the defects at interfaces, which is helpful for hindering the reversal domain nucleation [2, 3], as shown in Figs. 1(d1) to (d3). The modified GBs by AlCu diffusion also are effective for crack bridging or buffering, and exhibit an enhanced chemical stability. The high-abundance elements La/Ce based diffusion sources are also investigated in this work. The present results indicate that GBD of the HRE-free low-melting alloys can be used to effectively improve both the magnetic and service performance of Nd-Fe-B magnets due to the optimized microstructure.

![](https://assets.underline.io/uploads/markdown_image/1/image/1d95088594a90e4bd612c377f5970c41.jpg)

A strategy to enhance magnetic and service performance of Nd-Fe-B magnets by HRE-free grain boundary diffusion

**Session chair:** Wei Tang, Ames Laboratory



DOB - Permanent Magnets and Processing I

technical paper

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This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

Jiayi He

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Effects of deformation ratio and temperature on microstructure and properties of NdFeB magnets by one-step hot deformation

A strategy to enhance magnetic and service performance of Nd-Fe-B magnets by HRE-free grain boundary diffusion

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