Microstructure and Magnetic Properties of NdFeB Sintered Magnets Diffusion-Treated with Cu/Al Mixed Dyco Alloy-Powder

Abstract

We investigated the microstructural and magnetic property changes of DyCo, Cu + DyCo, and Al + DyCo diffusion-treated NdFeB sintered magnets. The coercivity of all diffusion treated magnet was increased at 880ºC of 1 st post annealing(PA), by 6.1 kOe in Cu and 7.0 kOe in Al mixed DyCo coated magnets, whereas this increment was found to be relatively low (3.9 kOe) in the magnet coated with DyCo only. The diffusivity and diffusion depth of Dy were increased in those magnets which were treated with Cu or Al mixed DyCo , mainly due to comparatively easy diffusion path provided by Cu and Al because of their solubility with Ndrich grain boundary phase. The formation of Cu/Al-rich grain boundary phase might have enhanced the diffusivity of Dy-atoms. Moreover, relatively a large number of Dy atoms reached into the magnet and mostly segregated at the interface of Nd 2 Fe 14 B and grain boundary phases covering Nd 2 Fe 14 B grains so that the core-shell type structures were developed. The formation of highly anisotropic (Nd, Dy) 2 Fe 14 B phase layer, which acted as the shell in the core-shell type structure so as to prevent the reverse domain movement, was the cause of enhancing the coercivity of diffusion treated NdFeB magnets. Segregation of cobalt in Nd-rich TJP followed by the formation of Co-rich phase was beneficial for the coercivity enhancement, resulting in the stabilization of the metastable c-Nd 2 O 3 phase.

Mg2+ and Cu2+ Charging Agents Improving Electrophoretic Deposition Efficiency and Coating Adhesion of Nano-TbF3 on Sintered Nd-Fe-B Magnets

“…It indicates that the addition of Mg 2+ and Cu 2+ had no effect on the TbF 3 coating GBD process. As an aside, the preparation of TbF 3 coating containing copper has some development prospects, because Cu can promote GBD by widening the grain boundary [ 27 ].…”

Application of a Dy3Co0.6Cu0.4Hx Addition for Controlling the Microstructure and Magnetic Properties of Sintered Nd-Fe-B Magnets

“…It is evident from Figures 6 and 7 that Co evinced the tendency to incorporate the 2:14:1 phase grains, while the Cu enriched triple junction phases. The role of Cu in the grain-boundary restructuring and positive effects of Co on the coercivities of Nd-Fe-B magnets were reported in our previous work [22] and were also considered in [23][24][25][26][27][28][29][30][31].…”

“…The magnetic properties (jHc) of the magnets (see Table 4 and Figure 8) prepared with the hydrogenated Dy3Co0.6Cu0.4 alloy were lower than those in the case of the application of the addition of the DyH2 [31]. One of the causes is the incomplete hydrogenation of the alloy (see Figure 3, XRD data) and, therefore, the incomplete occurrence of the grain boundary diffusion of the available Dy.…”

“…The grain boundary restructuring, with rare-earth-rich low-melting compounds added to low-alloyed Nd-Fe-B-based compositions in the course of technological processing, was realized when using (Pr,Nd) 6 Fe 13 Cu [4], Dy 32.5 Fe 62 Cu 5.5 [5], Dy 69 Ni 31 [6], Dy 88 Mn 12 (wt.%) [11], Pr 34.4 Co 65.6 (wt.%) [12], and Dy 82.3 Co 17.7 (wt.%) [13], which is a low-melting eutectic composition. It was shown that the intrinsic coercivity evidently increased when using Dy 82.3 Co 17.7 and the maximum intrinsic coercivity was achieved when its content was 2 wt.%.…”

Sintered permanent magnets prepared from hydrogenated (Nd-Fe-b strip-cast alloy + pr3(Co,cu) compound) mixture

“…The other components will improve the grain boundary structure via enhanced wettability between the Nd2Fe14B-based grains and the Nd-rich phase and decreasing exchange coupling between Nd2Fe14B-based grains [14,15]. According to [12], cobalt, in using Tb3Co0.6Cu0.4Hx addition, forms core/shell microstructure, which favors the improved thermal stability of coercive force [16].…”