Materials Science for High-Performance Permanent Magnets: Nd-Fe-B Processing / New RE-lean Hard Magnets
Sponsored by: TMS Functional Materials Division, TMS: Magnetic Materials Committee
Program Organizers: Satoshi Hirosawa, National Institute for Material Science; Matthew Kramer, Iowa State University; Oliver Gutfleisch, Technische Universität Darmstadt; Hae-Woong Kwon, Pukyong National University

Wednesday 8:30 AM
March 1, 2017
Room: 24C
Location: San Diego Convention Ctr

Funding support provided by: Elements Strategy Initiative Center for Magnetic Materials

Session Chair: Oliver Gutfleisch, Technical University Darmstadt; Konstantin Skokov, Technical University Darmstadt

8:30 AM  Invited
Prospects for Advanced Manufacturing of Magnets: Scott McCall1; 1LLNL
    Traditional manufacturing processes for rare earth magnets are based on powder metallurgy. A sequence of sintering and heat treating creates boules of magnetic material which then undergo dicing and grinding to desired shapes which can result in material losses above 50% when producing small magnets such as used in consumer electronics. Additive manufacturing offers (near) net shape production, largely eliminating material losses. Unfortunately, many of these techniques involve melting of powders which is an anathema to retaining large coercivity in permanent magnets. In this presentation we describe zero-loss additive techniques for producing near net shape SmCo5 magnets with intrinsic coercivities in excess of 50 kOe. These are amenable to producing complex shapes as well as compositional grading which may enable bulk exchange coupled magnets.

8:55 AM  
Microstructure Formation of Strip-cast R-Fe-B Alloys for Magnets: Kazuhiko Yamamoto1; Masashi Matsuura2; Satoshi Sugimoto2; 1Santoku Corporation; 2Tohoku University
    The purpose of this study is to clarify the microstructure formation in R-Fe-B strip-cast alloys, from nucleation to dendrite growth. Microstructure was observed using optical microscopy and field emission electron probe micro-analyzer. The nucleation area called the “disc” by Biloni et al., and pre-dendrites were observed in the vicinity of dimples distributed on the chilled surface in contact with the cooling roll. The discs was consisted of rare-earth elements (R) and Fe in the atomic ratio = 1:2, implying a Laves phase RFe2 composition. The pre-dendrites consisted of dendrites growing outward in all directions from the disc containing the fine R2Fe14B particles. The dendrites seemed to grow from the pre-dendrite, preferentially along the direction of thermal flow. Since these discs observed in the super-cooled area influence magnet fabrication adversely, it is important to avoid excessive super-cooling to obtain the preferred magnetic properties.

9:15 AM  
Texture Development Mechanism in HDDR Processed Nd-Fe-B Magnet: Tae-Hoon Kim1; Jung-Goo Lee2; Hae-Woong Kwon3; Cheol-Woong Yang1; 1Sungkyunkwan University; 2Korea Institute of Materials Science; 3Pukyong National University
    The hydrogenation-disproportionation-desorption-recombination (HDDR) process is an effective method to produce anisotropic Nd-Fe-B powders with grain refinement to single domain level. The HDDR process consists of hydrogenation of the Nd2Fe14B phase, subsequent disproportionation into NdH2, Fe2B and α-Fe, the desorption of hydrogen from the hydride, and finally, recombination to form the original Nd2Fe14B phase. Anisotropy related to texture of Nd-Fe-B powder can be controlled by careful control of processing parameters and extensive research on orientation relations between disproportionated phases and Nd2Fe14B phase has been carried to gain an understanding of texture inducement. However, no direct observation of the c-axis transition in Nd2Fe14B phase because HDDR treatment produces plenty of cracks in powder. In this study, texture memory in terms of the c-axis orientation was directly observed. The orientation of the initial Nd2Fe14B was recovered by Fe2B phase during HDDR process and the mechanism was investigated in consideration of crystallography.

9:35 AM  
Magnetic Anisotropy and Crystallographic Alignment in d-HDDR Process of Nd-Fe-B-Ga-Nb Powders: Takashi Horikawa1; Masashi Matsuura1; Satoshi Sugimoto1; Masao Yamazaki2; Chisato Mishima2; 1Tohoku University; 2Aichi Steel Corporation
     It is well known that by applying the dynamic-hydrogen disproportionation desorption recombination (d-HDDR) process to Nd-Fe-B magnet powders with an adequate hydrogen pressure, the resultant powders exhibit a high magnetic anisotropy owing to the crystallographic alignment of the recombined Nd2Fe14B grains. To understand the details of the alignment states during d-HDDR process, effects of treatment conditions on the crystallographic orientation were investigated. A characteristic orientation relationship between Fe and NdH2 grains was observed and it was suggested that this relationship was related to a microstructure of samples after the HD stage. The difference in the hydrogen pressure during the HD stage may result in the variation of such a microstructure and the resultant size of divisions in "local texture" in which the recombined Nd2Fe14B grains are highly aligned. This work was supported by the Future Pioneering Projects/Development of Magnetic Material Technology for High-Efficiency Motors from NEDO, Japan.

9:55 AM Break

10:10 AM  Invited
Recent Developments in RFe12-type Compounds for Permanent Magnets: A.M. Gabay1; George Hadjipanayis1; 1University of Delaware
    A new rare-earth-free uniaxially anisotropic ZrFe10Si2 compound has been discovered, and R1-xZrxFe10Si2 compounds with R = Ce, Sm were proposed for the development of magnets that are minimally reliant on the rare earth elements. The newly employed mechanochemistry proved to be an attractive synthesis technique having produced in particular a submicron Sm0.7Zr0.3Fe10Si2 powder with a coercivity of 10.8 kOe and a calculated maximum energy product of 13.8 MGOe. At the same time, little progress has been made in the fabrication of fully dense -type RFe12 magnets because of the inherent instability of the nitrides and the unfavourable phase equilibria involving the more stable compounds. The work was supported by U.S. Department of Energy DOE-DE-FG02-90ER45413 and University of Delaware Energy Institute.

10:35 AM  
Temperature Dependence of the Magnetization and Magnetic Anisotropy Measured on the Epitaxial RFe12 (-Nx) (R = Sm and Nd) Thin Films with ThMn12 Structure: Yusuke Hirayama1; Yukiko Takahshi1; Satoshi Hirosawa1; Kazuhiro Hono1; 1National Institute for Materials Science
    We have prepared NdFe12 and SmFe12 epitaxial films and their nitrides without a structure stabilized element by using a co-sputtering system in order to evaluate their temperature dependence of the magnetic properties. By nitriding, the Curie temperature was increased by more than 200°C for both NdFe12 and SmFe12 films. The saturation magnetization of 1.66 T and 1.58 T at room temperature were obtained for NdFe12Nx [1] and SmFe12, respectively, with the uniaxial anisotropy in the out of plane direction which corresponds to the c-axis of the ThMn12 structure, supporting the first principal calculations [2,3]. We also present the temperature dependence of the magnetization and magnetic anisotropy and discuss the results in terms of the classical molecular field picture. [1]Y. Hirayama et. al., Scripta Materialia. 95(2015)70. [2]Y. Harashima et. al., JPS Conf. Proc. 5(2015) 011021. [3]W. Körner et al., Scientific Reports 6 (2016)24686.

10:55 AM  
New Hard Magnetic ThMn12-type phases with Low Rare Earth Contents for Permanent Magnet Applications: Andrés Martín-Cid1; Daniel Salazar1; Aleksander Gabay2; Ana María Schönhöbel1; Jose Garitaonandia3; Jose Manuel Barandiaran3; George Hadjipanayis2; 1BCMaterials; 2University of Delaware; 3University of the Basque Country (UPV/EHU)
     In recent years, the critical supply of the raw rare-earth materials, has motivated the search for and rare earth-free and rare-earth-lean hard magnetic materials. Tetragonal R(Fe,M)12 compounds (R = rare earth), with the ThMn12 phase structure, have long been of interest as permanent magnet materials with reduced R content, but some stability issues have to be overcome first. To further exploit the advantage of low R content, particular attention has been recently paid to compounds with cerium, the most abundant and least “critical” rare earth metal. Zr substitution for Ce in the CeFe10Si2 and Sm for Ce in the CeFe9Co2Ti alloys stabilizes the 1:12 structure. The alloys have a single ThMn12 phase at several substitutions. High magnetization (>100emu/g), Curie temperatures >300ºC and coercivity enhanced by Zr and Sm substitutions, make them suitable for permanent magnet applications.This work has been funded by the EU-Horizon2020 project NOVAMAG-686056 and DOE-DE-FG02-90ER45413.

11:15 AM  Invited
First-principles Study of ThMn12-type Iron-based Rare-earth Intermetallics: Takashi Miyake1; 1AIST
    Synthesis of NdFe12N film by Hirayama et al. [1] has attracted renewed interest in the ThMn12-type compounds. Although NdFe12N has large saturation magnetization and reasonably strong magnetocrystalline anisotropy [2], its thermodynamic instability prevents industrial applications. We have performed density functional calculations of NdFe11M for M=Ti, V, Cr, Mn, Co, Ni, Cu, Zn. We found that Co can contribute to phase stability, and NdFe11CoN has large saturation magnetization and crystal-field parameter A20 comparable to NdFe12N. We also found that the magnetic exchange coupling between Nd and Fe has a big impact on magnetic anisotropy at high temperatures, and the strength of the coupling varies significantly by interstitial nitrogenation. [1] Y. Hirayama et al., Scripta Materialia 95, 70 (2015). [2] T. Miyake et al., J. Phys. Soc. Jpn. 83, 043702 (2014).