Abstract
Permanent magnets (PM) are critical components for electric motors and power generators. Key properties of permanent magnets, especially coercivity and remanent magnetization, are strongly dependent on microstructure. Understanding metallurgical processing, phase stability and microstructural changes are essential for designing and improving permanent magnets. The widely used PM for the traction motor in electric vehicles and for the power generator in wind turbines contain rare earth elements Nd and Dy due to their high maximum energy product. Dy is used to sustain NdFeB's coercivity at higher temperature. Due to the high supply risk of rare earth elements (REE) such as Dy and Nd, these elements are listed as critical materials by the U.S. Department of Energy and other international institutes. Other than Dy, finer grain size is also found to have effect on sustaining coercivity at higher temperature. A proper control of phase stability and microstructures has direct impact on mitigating REE supply risk. Compared to rare earth PMs, non-rare earth (non-RE) PMs typically have lower maximum energy products, however, given their small supply risks and low cost, they are being intensively investigated for less-demanding applications. The general goal for the development of non-RE PMs is to fill in the gap between the most cost-effective but low performing hard ferrite magnet and the most expensive but high performing RE PMs. In the past five years great progress has been made toward improving the microstructure and physical properties of non-RE PMs. Several new candidate materials systems were investigated, and some have showed realistic potential for replacing RE PMs for some applications. In this article, we review the science and technology of various types of non-RE materials for PM applications. These materials systems include Mn based, high magnetocrystalline anisotropy alloys (MnBi and MnAl compounds), spinodally decomposing alloys (Alnico), high-coercivity tetrataenite L10 phase (FeNi and FeCo), and nitride/carbide systems (such as α" based, high saturation magnetization Fe16N2 type phase and Co2C/Co3C acicular particle phase). The current status, challenges, potentials as well as the future directions for these candidates non-RE magnet materials are discussed.
Highlights
NdFeB magnets are widely used for conversion between electricity and mechanical energy
Compared to rare earth Permanent magnets (PM), non-rare earth PMs typically have lower maximum energy products, given their small supply risks and low cost, they are being intensively investigated for less-demanding applications
L10-FeNi is one of the few non-rare earth elements (REE) materials that has the potential to reach the level of the (BH)max of RE permanent magnets
Summary
NdFeB magnets are widely used for conversion between electricity and mechanical energy. Subsequent cold-iso-press at 345 MPa and annealing at 500 K for 1 h will yield about 88% density with 6.6 kOe coercivity and 8.3 MGOe at room temperature It is possible warm-iso-press at 500 K with large stress may further improve density to over 96% and maximum energy product over 10 MGOe. One approach to improve the energy product of a-MnBi is to take advantage of its large magnetocrystalline anisotropy and exchange couple the a-MnBi with a soft phase such as Fe, FeB, Co and. The difference is that the a-MnBi nanoparticle were obtained using metalredox method and FeCo nanowires were electro-spun In both cases, the overall energy product of the composite was less than 6 MGOe, mainly due to the large amount of impurities that are difficult to remove after the solution based chemical synthesis. Exchange coupling of MnBi with Co has an attractive outcome but cleanly and uniformly coating MnBi powder with just 3 nm of Co is a grand challenge
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
