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Nanostructured Hf-Co and Nd-Fe-B Hard Magnetic Materials
In recent years, growing concerns about the environment and natural resources have driven the search for more energy efficient electric machines, such as wind turbine generators and traction motors. Rare-earth permanent magnets are essential components of those applications. However, the availability and high price of rare-earth elements have been a major problem since China limited the exportation of these materials in 2009. To reduce the stress on the supplement of rare-earth materials, efforts have been put to develop rare-earth free hard magnetic materials as well as rare-earth magnets with improved magnetic performance. The Hf-Co-based alloys, which have shown promise as a rare-earth free hard magnetic material, were investigated in this research. The magnetic properties and microstructures of HfCo7 alloy were studied using melt spun technique. The best magnetic performance (Hc=2.2 kOe, (BH) max∼5 MGOe) was observed at 30 m/s. The good magnetic properties were attribute to the exchange coupling between the hard magnetic phase and the hcp Co secondary phase. Further, Co-rich planar defects were observed in the 10 m/s sample and these defects are considered to affect the composition of the hard magnetic phase. The effects of B and Fe additions on the magnetic properties of Hf-Co alloys were also discussed. Nd-Fe-B single crystal hard magnetic nanoparticles were successfully produced by appropriate alloy design and low energy mechanical milling process. Intergranular fracture was achieved by alloying S to the Nd-Fe-B alloys during low energy ball milling. The milling conditions were tailored to produce gentle forces that break the bulk materials into nanoparticles, minimizing structural damage to the particles. Low energy ball milling at 50 rpm with weight ratio of 60/1 yields the most single-crystal nanoparticles, and the coercivitiy of the 72 h milled powders is as high as 6.1 kOe, a degree of alignment of 0.19 were obtained.
Wang, Meiyu, "Nanostructured Hf-Co and Nd-Fe-B Hard Magnetic Materials" (2017). ETD collection for University of Nebraska-Lincoln. AAI10273588.