| Advances in Permanent Magnets George Hadjipanayis1; 1UNIVERSITY OF DELAWARE, Newark, United States; PAPER: 427/SISAM/Plenary (Oral) SCHEDULED: 11:45/Thu. 24 Oct. 2019/Dr. Christian Bernard ABSTRACT: In this presentation, the current trends and the latest developments in the field of the permanent magnets will be reviewed. Two powerful factors shape the current developments of the rare-earth magnets, the rapidly growing demand for high-energy-density magnets operating at 150 – 200 °C and the echo of the 2010-11 rare earths supply crisis. The incentive for increasing the operating temperature of the Nd-Fe-B magnets using smaller amounts of heavy rare earths has resulted in the development of localized alloying techniques, in which Dy or Tb are delivered to the exact locations in the magnet through grain-boundary infiltration. Moreover, the same infiltration approach as well as a more refined micro-alloying now allows for sintered and die-upset Nd-Fe-B magnets exhibiting a coercivity as high as 20 kOe without any use of the heavy rare earths. To address the sustainability challenge, researchers and manufacturers are also partially replacing even the light rare earths, Nd and Pr, with the more abundant Ce and La. The Sm-Co magnets had their maximum energy product recently increased to 35 MGOe, primarily through a greater Fe substitution for Co. The ThMn12-type compounds, notable for their naturally low rare earth content see a renewed interest. Although 1:12 alloys with excellent fundamental properties – rivaling those of the Nd2Fe14B compound – have been synthesized and processed by different approaches ranging from sintering followed by infiltration to mechanochemistry, there has not yet been a breakthrough in preparation of practical 1:12 magnet. Such breakthrough apparently happened this year for the most developed rare-earth-free permanent magnet material (not counting the prohibitively expensive FePt). Magnetic-field annealing of a properly alloyed MnBi alloy, after it has been subjected to melt spinning and warm compaction, produced magnets exhibiting a maximum energy product of 11-12 MGOe, which is 40% greater than those obtained via the traditional powder metallurgy and which must be sufficient to replace the lower grades of the rare earth magnets. |
