Improvement of coercivity and thermal stability of Nd-Fe-B sintered magnets by intergranular addition of Tb80Fe20 alloy

Abstract To improve the coercivity and temperature stability of Nd-Fe-B sintered magnets for high-temperature applications, the eutectic Tb80Fe20 (wt%) alloy powders were intergranular added into the Nd-Fe-B sintered magnets to enhance the coercivity (Hcj) and thermal stability. The microstructure, magnetic properties and thermal stability of the Nd-Fe-B magnets with different Tb80Fe20 contents were studied. The experimental results demonstrate that the coercivity (Hcj) of the sintered Nd-Fe-B magnet is significantly enhanced to 27.78 kOe from 14.12 kOe, and the remanence (Br) decreases not obviously by introducing 4 wt% Tb80Fe20 alloy. Meanwhile, the reversible temperature coefficients of coercivity (β) and remanence (α) of the Nd-Fe-B magnets are increased from −0.5634%/°C to −0.4506%/°C and −0.1276%/°C to −0.1199%/°C at 20–170 °C, respectively. The Curie temperature (TC) of the Nd-Fe-B magnet is slightly enhanced with the increase of Tb80Fe20 content. Moreover, the irreversible flux magnetic loss (hirr) is obviously reduced as Tb80Fe20 addition. Further analysis of the microstructure revealed that a modified microstructure, i.e. clear and continuous RE-rich grain boundary layer, is acquired in the sintered magnets by introducing Tb80Fe20 alloy. The associated mechanisms on improved coercivity and thermal stability are comprehensively researched.