High coercivity, anisotropic, heavy rare earth-free Nd-Fe-B by Flash Spark Plasma Sintering

Area of Science:

• Materials Science
• Magnetism
• Nanotechnology

Background:

• Reducing Heavy Rare Earth (HRE) content in permanent magnets is crucial for sustainable green technologies.
• HREs enhance high-temperature performance in Neodymium-Iron-Boron (Nd-Fe-B) magnets.
• Achieving high-temperature properties without HREs requires a textured nanoscale grain structure, typically via costly methods.

Purpose of the Study:

• To investigate Flash Spark Plasma Sintering (FSPS) as an efficient method for producing HRE-free Nd-Fe-B magnets.
• To optimize the FSPS process for achieving a desirable nanoscale grain structure.
• To compare the magnetic properties of FSPS-processed magnets with conventionally processed ones.

Main Methods:

• Application of Flash Spark Plasma Sintering (FSPS) with rapid sinter-forging to Dy-free Nd-Fe-B melt-spun powder (MQU-F).
• Microstructural analysis using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) for process optimization.
• Direct comparison of the optimized FSPS material with commercial die-upset forged (MQIII-F) material.

Main Results:

• FSPS achieved near theoretical density in a 10-second process, demonstrating rapid and efficient production.
• Optimized FSPS samples exhibited a halved grain size compared to commercial die-upset forged (MQIII-F) material.
• The FSPS material showed a 14% increase in coercivity (1438 kA/m) and matched remanence (1.16 T), resulting in a BHmax of 230 kJ/m³.

Conclusions:

• FSPS is a viable and efficient technique for producing high-performance, HRE-free Nd-Fe-B magnets.
• The refined microstructure achieved via FSPS leads to significantly improved magnetic properties, particularly coercivity.
• This method offers a cost-effective alternative to traditional die-upset processing for advanced magnet applications.