MARGARIT GJOKA, CHARALAMPOS SARAFIDIS, DIMITRIS NIARCHOS, GEORGE C. HADJIPANAYIS
Abstract
The development of high-performance permanent magnets free from critical rare-earth elements is a crucial goal for sustainable technologies like electric vehicles and wind turbines. ThMn12-type (1:12) alloys are promising candidates due to their strong magnetic properties, high Curie temperature, and rare-earth-lean composition. The primary objective of this research was to maximize the energy product ((BH)max, a critical performance metric for permanent magnets, in rare-earth-lean ThMn12-type alloys. The investigation demonstrates a pathway to significantly enhance this parameter through careful compositional and processing control. A key achievement of this work is the attainment of an exceptional energy product of approximately 289 kJ/m3 in a Sm(Fe,Co,Ti)12-based alloy with a strategically modified composition Sm0.75Zr0.25Fe9.04Co2.26Ti0.7. The study systematically explored alloys synthesized via arc melting, followed by high-energy ball milling (HEBM) and annealing. While Zr doping was found to slightly decrease coercivity compared to the baseline SmFe9Co2Ti alloy, its inclusion was fundamentally vital for achieving the standout energy product in the Ti-reduced composition. Microstructural analysis confirmed that extended milling times refined the grain structure, which is essential for enhancing magnetic properties. However, the delicate balance between promoting the desired magnetic phase and preventing the formation of detrimental phases, such as Sm2O3 and soft
Key words: ThMn12-type alloys, permanent magnets, high-energy ball milling, coercivity, Zirconium doping, energy product.