Obtain high coercivity of Nd–Ce–Fe–B magnet via grain boundary diffusion with Dy80Al10Cu10 alloy

Abstract

Dy80Al10Cu10 and DyH3 were employed as diffusion sources to perform grain boundary diffusion (GBD) on 7 wt% Ce containing Nd-Fe-B magnets. The coated samples underwent a heat treatment at 1193.2 K for 6 h, followed by an annealing process at 913.2 K for 5 h. As a result, the coercivity increased from the original 1268.0 kA/m to 1681.1 kA/m and 1618.2 kA/m in Dy80Al10Cu10 and DyH3 diffused magnets, respectively. Notably, Dy80Al10Cu10 exhibited a more pronounced diffusion effect than DyH3. After GBD, continuous intergranular phases were observed around the matrix grains, which weakening the magnetic coupling effect between the ferromagnetic matrix grains, which in turn improved coercivity. Microstructure analysis revealed the presence of CeFe2 phase, which impeded the effectiveness of GBD due to its high melting point. However, when Dy80Al10Cu10 was employed as the diffusion source, the detrimental impact of CeFe2 was better inhibited compared to DyH3. The inclusion of Cu and Al elements in the Dy80Al10Cu10 alloy optimized the wettability and facilitated the formation of an antiferromagnetic RE6Fe13Cu phase at the triple junctions (TJs), which leads to the depletion of Fe and enrichment of RE in adjacent GBs. Furthermore, Cu aided in dissolving high melting point CeFe2 and promoting the formation of GBs with improved wettability, thereby contributing to an increase of coercivity.