Tomaž Tomše

Abstract:

The green transition drives the advancement of sustainable energy conversion technologies. Nd-Fe-B permanent magnets are crucial components of energy-efficient electric motors and generator systems. Presently, state-of-the-art magnets, boasting maximum energy products as high as 450 kJ/m³, are produced through powder metallurgy routes. However, conventional sintering is energy-intensive and offers limited control over microstructure formation and the final magnet's geometry.

Rapid powder consolidation techniques, like Spark Plasma Sintering (SPS), present notable advantages over conventional methods. They offer faster and more energy-efficient sintering processes, lower sintering temperatures, and the potential for net-shape manufacture, promising a new generation of Nd-Fe-B magnets with improved functionalities. Yet, due to the strong structure-properties dependence, consolidation of microcrystalline Nd-Fe-B-type powders via SPS proved challenging. Localized overheating at particle-particle contacts, owing to the Joule effect, can disrupt the delicate phase composition of the material, resulting in a drastic loss of hard-magnetic performance [1, 2]. 

Through careful optimization of heating conditions and the introduction of novel concepts in processing multiphase metallic systems like Nd-Fe-B, our research has been focused on developing alternative sintering strategies for the manufacture of Nd-Fe-B magnets. Fast sintering cycles have been employed to enhance the material's high-temperature performance by suppressing grain growth during densification. We will show that rapid sintering can reduce the energy consumption required to densify an Nd-Fe-B-type powder by an order of magnitude compared to slow conventional sintering. The new powder consolidation paradigms are applicable for processing both fresh and recycled powders, offering great potential for reengineering the magnet's microstructure, and having implications for future industrial processes.