Journal
IEEE TRANSACTIONS ON MAGNETICS
Volume 58, Issue 2, Pages -Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TMAG.2021.3102513
Keywords
Coercivity; melt-spinning; rare-earth magnets; ThMn12
Funding
- U.S. Department of Energy [DE-FG02-90ER45413]
- U.S. Department of Energy (DOE) [DE-FG02-90ER45413] Funding Source: U.S. Department of Energy (DOE)
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This study focuses on the development of hard magnetic properties in Sm(Fe,Co)(12)-based compounds through nanostructuring and powder metallurgy. The addition of Zr and B elements can significantly enhance the magnetic properties of the alloys. The research provides insights into the effects of alloy structure and solidification rates on the magnetic performance.
Permanent magnets made from Sm(Fe,Co)(12)-based compounds are being actively pursued through nanostructuring and powder metallurgy. This study was aimed at the development of hard magnetic properties in bulk as-cast alloys and in melt-spun alloys for very low wheel speeds. Slower solidification rates and alloying with Zr promote the tetragonal ThMn12-type crystal structure, whereas higher solidification rates and alloying with B replace the ThMn12 structure type with the TbCu7 structure type. When introduced simultaneously, Zr and B dramatically reduce the alloy solidification rates required for both the refinement of the 1:12 crystallites and their replacement with the 1:7 phase. In bulk arc-melted alloys, this allowed for a microstructure of separated 1:12 crystallites 1-3 mu m in size, although, because of the ferromagnetic nature of a minority phase, the coercivity of these fine-grained alloys reached only 0.73 kOe. A moderately accelerated solidification further refined the 1:12 crystallites and increased the coercivity; a Sm0.7Zr0.4(Fe,Co)(10.8)Ti0.7B0.5 alloy exhibited a coercivity of 1.5 kOe and a maximum energy product of 3.4 MGOe when it was melt-spun into a 0.26 mm-thick ribbon. A more rapid solidification suppressed the 1:12 phase, and after annealing at 800 degrees C-850 degrees C, the alloys modified with Zr and B developed reasonably high coercivity and maximum energy product even when melt-spun at a wheel speed of 6 m/s. For the above-mentioned alloy, these values were 4.1 kOe and 7.8 MGOe, respectively. A similarly processed very-Sm-lean Sm0.5Zr0.6(Fe,Co)(10.6)Ti0.7B0.7 alloy exhibited a remanence of 8.8 kG and an energy product of 7.4 MGOe.
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