Dual-alloy Method Research Articles

Effect of Rare-Earth Content on Coercivity and Temperature Stability of Sintered Nd-Fe-B Magnets Prepared by Dual-Alloy Method

The influence of rare earth content on coercivity and temperature stability with dual-alloy method has been investigated. It is found that the coercivity of magnets increases rapidly firstly and then slightly with the increasing of rare earth content from the range of 29.5 wt% to 33.5 wt%. The coercivity and the temperature coefficient of coercivity will get better with rare earth content of 31.5 wt%. The result of magnetic anisotropy field of magnet revealed that it almost has no change with different rare-earth content. Scanning electron microscopy (SEM) and Transmission electron microscope (TEM) revealed that continuous thin layers of Nd-rich phase about 4 nm were found along the grain boundaries in the annealed sample at 31.5 wt% rare earth content, while the grain boundary width of magnet exceeds 8 nm at 33.5 wt%.

Dysprosium Diffusion Behavior and Microstructure Modification in Sintered Nd-Fe-B Magnets via Dual-Alloy Method

Dysprosium diffusion and microstructure alteration behaviors in sintered Nd-Fe-B magnets via dual-alloy method have been investigated. The sintered magnets were prepared by blending Dy-free and Dy-rich powders with varying proportions. Results indicate that Dy element has already diffused from Dy-rich powders into the 2:14:1 phase of Dy-free powders and tended to homogenize in the bulk magnet, attributed to the coalescence of grains and dysprosium element concentration gradient. In addition, Dy and Pr/Nd elements counterdiffusion process redistributes the grain boundaries homogeneously. The fracture surfaces of magnets prepared via dual-alloy method almost appear intergranular fracture. It demonstrates that both of (Nd/Pr, Dy) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B phase formation and microstructure alteration have favored to coercivity enhancement and thermal stability improvement of the magnets.