Study of sintered Nd-Fe-B magnet with high performance of Hcj (kOe) + (BH)max (MGOe) > 75

Abstract

We have developed a Nd-Fe-B sintered magnet of extremely high performance. The intrinsic coercivity Hcj is as high as 35.2 kOe (2803kA/m) together with the maximum energy product (BH)max of 40.4 MGOe (321.6kJ/m3). These values result in Hcj (kOe) + (BH)max (MGOe) > 75. Between 293 K (20ºC) and 473 K (200ºC), the temperature coefficients of remanence and intrinsic coercivity are αBr = −0.122 %/°C and αHcj = −0.403%/°C, respectively. A maximum operating temperature of 503 K (230ºC) is obtained when permeance coefficient Pc = −B/H = 2. Grain boundary diffusion (GBD) technique on magnet surface has been developed to increase Hcj by 3.6 kOe without significantly decrease of Br and (BH)max. The intrinsic coercivity of the GBD treated magnet Hcj(C) has a linear relationship with that of the untreated magnet Hcj(B) between 200 K and 473 K (in unit of kOe): Hcj(C) = 1.03Hcj(B) + 2.38. The enhancement of Hcj by GBD treatment has contributions not only from the improvement of microstructure but also from the increase of Ha in the grain surface layer. It is also found that GBD treatment brings no deterioration in corrosion resistance of untreated magnet.

Coercivity enhancement of Dy-free Nd–Fe–B sintered magnets by intergranular adding Ho63.4Fe36.6 alloy

“…However, due to serious thermal demagnetization, the relatively low coercivity cannot meet growing requirements of high-temperature applications, such as hybrid electric vehicles and wind power generators [2][3][4]. This obstacle can be solved by increasing the room temperature coercivity.…”

High performance RE–Fe–B sintered magnets with high-content misch metal by double main phase process

“…Due to the outstanding magnetic properties, Nd-Fe-B based permanent magnets have been widely applied in various fields ranging from sensors, hybrid vehicles, wind generators to electronic devices. [1,2] The continuously growing demand of Nd-Fe-B magnets has led to the overspending of the closely-relied Pr, Nd, Dy, and Tb metals, whereas, high abundant La and Ce are overstocked. In order to balance the use of rare earth resources, La or Ce substitution for Nd to prepare RE-Fe-B (RE, rare earth) magnets have attracted worldwide attention again.…”

Magnetic domain switching in Nd–Fe–B sintered magnets with superior magnetic properties

“…Based upon above approaches, one can obtain new Nd-Fe-B sintered magnets with both high H ci and high (BH) max , which could have a wider application field [19][20][21]. Moreover, the new magnets, containing less Dy or Tb, will have low fabrication costs compared with the present Nd-Fe-B sintered magnets.…”

“…More investigations to the micromagnetic structure of the magnets are necessary to understand the nature of the coercivity enhancement [22,23]. In this paper, we describe a novel approach to develop Nd-Fe-B sintered magnets with (BH) max of 38.5 MGOe and H ci of 47.1 kOe, leading to a record high overall magnetic performance (OMP) [19] of (BH) max (MGOe) + H ci (kOe) = 85.6. These superior magnetic properties, in particular the giant coercivity, enable Nd-Fe-B sintered magnets to compete for wider applications at an elevated temperature.…”