Temperature-dependent Dy diffusion processes in Nd–Fe–B permanent magnets

Effect of DyF3 and TbF3 additions on the coercivity enhancement in grain boundary diffusion processed Nd-Fe-B permanent magnets

“…Same with the previous investigations [1,5,7], our experiment exhibited that happen increasing the coercivity of sintered Nd-Fe-B permanent magnet after conducting the GBDP using the temperature up to 900°C by both Dy or Tb additions, and then the coercivity decreased if temperatures going up above than 900°C. The diffusion of Dy or Tb into the inside of the magnets was strongly dependent on temperature.…”

“…The coercivity of sintered Nd-Fe-B permanent magnets can be significantly increased by partial substitution of Nd by Dy or Tb elements, because both Dy2Fe14B and Tb2Fe14B phase has much higher magnetocrystalline anisotropy field than that of Nd2Fe14B [1,[4][5][6][7]. Same with the previous investigations [1,5,7], our experiment exhibited that happen increasing the coercivity of sintered Nd-Fe-B permanent magnet after conducting the GBDP using the temperature up to 900°C by both Dy or Tb additions, and then the coercivity decreased if temperatures going up above than 900°C.…”

“…During GBDP at elevated temperature, DyF3 or TbF3 diffuses along the grain boundaries and simultaneously reacts with the Nd-rich phase [10], and leads to a microstructure with grains that exhibit a HRE-rich (Nd,Dy/Tb)2Fe14B shell and a HRE-poor core [1]. During tempering at 500°C, Nd2Fe14B grains were surrounded by Dy/Tb-rich liquid phase which then solidified during cooling and formed a (Nd,Dy/Tb)2Fe14B shell around the Nd2Fe14B grains [2,12].…”

“…NdFe-B permanent magnets exhibit excellent magnetic properties and currently widely used for some variety applications such as traction motors of electric (hybrid electric) vehicles, generators and transformers [1,2,[3][4][5][6][7]. However, the poor temperature stability of Nd-Fe-B magnets still makes it inapplicable in many potential fields requiring operating temperatures above 150°C [2,5,[7][8].…”

Synergetic Effect of Dy2O3 and Ca Co-Dopants towards Enhanced Coercivity of Rare Earth Abundant RE-Fe-B Magnets

“…The performance of these permanent magnets can be much enhanced through adjusting the microstructure. In addition, it has been widely reported that doping with heavy rare earth elements (Dy or Tb) is a highly useful way to improve the magnetic performance [15, 16], for example, by enhancing the coercivity and thermal stability. It was reported that both the coercivity and the thermal stability of Nd 2 Fe 14 B-type magnets can be enhanced through doping with Dy 70 Cu 30 [17, 18] or Dy 80 Al 20 [19].…”