Coercivity of the Nd–Fe–B hot-deformed magnets diffusion-processed with low melting temperature glass forming alloys

• Bulk-glass forming alloys were infiltrated into hot-deformed Nd–Fe–B magnets.
• Very high coercivity of 2.8 T was attained without heavy rare-earth elements.
• Approximately half of the inter-granular regions were amorphous.
• Crystallization of amorphous intergranular phase does not change coercivity.

Nd- and Pr-based alloys with bulk glass forming ability and low melting temperatures, Nd60Al10Ni10Cu20 and Pr60Al10Ni10Cu20, were used for grain boundary diffusion process to enhance the coercivity of hot-deformed magnets. The coercivity increment was proportional to the weight gain after the diffusion process. For the sample with 64% weight gain, the coercivity increased up to 2.8 T, which is the highest value for bulk Nd–Fe–B magnets that do not contain heavy rare-earth elements, Dy or Tb. Approximately half of the intergranular regions were amorphous and the remaining regions were crystalline. Magnetic isolation of the Nd2Fe14B grains by the Nd-rich amorphous/crystalline intergranular phases is attributed to the large coercivity enhancement. The coercivity does not change after the crystallization of the intergranular phase, indicating that the coercivity is not influenced by the strain at the interface with the crystalline intergranular phase.