Grain refinement and coercivity enhancement of sintered Nd–Fe–B alloys by doping eutectic alloy (Nd 0.75 Pr 0.25 ) 70 Cu 30.

Abstract

A significant enhancement in the coercivity and grain refinement was revealed for the spark plasma sintered NdFeB magnets by doping eutectic alloy (Nd_0.75Pr_0.25)₇₀Cu₃₀ powders. The commercially available NdFeB powders were mixed with (Nd_0.75Pr_0.25)₇₀Cu₃₀ powders (0, 2 and 5 wt.%) and then consolidated by spark plasma sintering at 700°C under 50 MPa. Microstructure analysis shows that the addition of (Nd_0.75Pr_0.25)₇₀Cu₃₀ alloy reduces the formation of coarse grain zone and decreases the average Nd₂Fe₁₄B grain size by intergranular phase modification. The RE-rich phase containing Nd, Pr at the Nd₂Fe₁₄B grain boundary caused the magnetic isolation effect. Hence, the coercivity increased from 18.3 kOe for un-doped NdFeB to 20.3 and 21.6 kOe with doping content of 2 and 5 wt.%, respectively. This study provides an economic way to fabricate sintered NdFeB magnets with enhanced coercivity and homogeneous nanostructure.