Optimizing the grain boundary structure of sintered Nd-Dy-Fe-Co-B magnets by low-melting-point alloys grain boundary addition

To respond to the gradually increasing demand for thermal stability of sintered NdFeB magnets and grasp the evolution rules of their phase structure, research on sintered Nd-Dy-Fe-Co-B magnets was conducted. The magnets used in this study were prepared by the powder metallurgy method (Strip Casting + Hydrogen Decrepitation + Jet Milling). The room temperature magnetic properties of the magnet sample were Br = 11.45 kGs and Hcj = 22.42 kOe, with a low-temperature coefficient of Br (αBr(20 °C∼100 °C) = −0.059 %/°C) and a high Curie temperature (Tc = 460 °C). Based on the microstructure observation, there were planar anisotropic soft magnetic phase Nd2Co17 within grain boundaries and the "Cu-Co Opposite Distribution". Low-melting-point binary alloy Pr80Cu20 was introduced into the magnet by grain boundary addition to eliminate Nd2Co17 phases and improve the coercivity. After the grain boundary addition, the "Cu-Co Opposite Distribution" was used to eliminate the Nd2Co17 phase, the grain boundary structure was optimized, and the coercivity was increased by approximately 2.6 kOe, which was approximately 10 % of the total coercivity. Therefore, Cu-containing low-melting-point binary alloy grain boundary addition is an effective method for optimizing the grain boundary structure of Nd-Dy-Fe-Co-B magnets, thereby improving the high-temperature stability and coercivity. •The "Cu-Co Opposite Distribution" was found in the Nd-Dy-Fe-Co-B magnets.•The planar anisotropic soft magnetic phase Nd2Co17 was found in grain boundaries.•Pr80Cu20 binary alloy grain boundary addition is an effective method for optimizing the grain boundary structure.•The orientation behavior of sintered NdFeB magnets cannot be changed by the substitution of Co.