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

Abstract

AbstractGrain 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.