Materials Science for High-Performance Permanent Magnets: Synthesis and Processing
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

Thursday 2:00 PM
March 2, 2017
Room: 24C
Location: San Diego Convention Ctr

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

Session Chair: Matthew Kramer, The Ames Laboratory; Satoshi Hirosawa, National Institute for Material Science

2:00 PM  Invited
Fabrication of Submicrometer-sized Sm2Fe17N3 Hard Magnetic Particles: Toshiharu Teranishi1; Hsin-Lun Wu1; Ryota Sato1; 1Kyoto University
    The hard magnetic particles containing light rare-earth element with high magnetocrystalline anisotropy have drawn great attention because of the potential application in high energy-product permanent magnets. The Sm2Fe17N3 hard magnetic particles prepared by introducing nitrogen atoms into the interstitial sites of the Sm2Fe17 alloy particles can be applied to high performance bonded magnets (saturation magnetization Ms = 1220 emu/cm3, anisotropy field Hk = 146 kOe, and Curie temperature Tc = 750 K). The particle size is one of the important factors for fabricating high energy-product permanent magnets. In this study, we report the fabrication of the Sm2Fe17N3 hard magnetic particles in submicrometer size from the Fe3O4/SmOx core/shell nanoparticles synthesized by the chemical approach.

2:30 PM  
Coercivity and Strength Enhancement of a Binder Jetted NdFeB Bonded Magnet by (Pr,Nd)-Cu-Co Alloy Infiltration: Ling Li1; Angelica Tirado1; Benjamin Conner1; Amy Elliott1; Orlando Rios1; Haidong Zhou2; M. Parans Paranthaman1; 1Oak Ridge National Laboratory; 2University of Tennessee
    Bonded NdFeB magnets have experienced a rapid increased usage in automobiles owing to their superior advantages such as complex shape, light weight, etc. Additive manufacturing (AM) enables rapid production with minimum materials waste, offering great potential for large-scale industrial applications. In this work, binder jetting AM technique is employed to fabricate isotropic NdFeB bonded magnets, followed by an infiltration process with low-melting eutectic alloys to enhance the mechanical and magnetic strength of the magnet product. Two alloys with nominal compositions Pr3Cu0.25Co0.75 (PrCuCo) and Nd3Cu0.25Co0.75 (NdCuCo) are diffused into the as printed porous parts in argon atmosphere at 700 °C to 750 °C for 1 - 6h. The intrinsic coercivity Hci of the as printed sample is enhanced from 9.2 kOe to 15.5 kOe (~68.5 %) and 16.9 kOe (~83.7%) after diffusion of PrCuCo and NdCuCo, respectively. The mechanism for the coercivity enhancement will be discussed in terms of microstructural observations.

2:50 PM  
Recent Developments in High Coercivity Nd-lean Nd-Fe-B Infiltrated Magnets: Daniel Salazar1; Andrés Martín-Cid1; Jose Garitaonandia2; Rajasekhar Madugundo1; Jose Manuel Barandiaran2; George Hadjipanayis3; 1BCMaterials; 2University of the Basque Country (UPV/EHU); 3University of Delaware
     Commercial high-energy permanent magnets (PM) need large amounts of critical and strategic raw materials, such as Dy and Tb, to obtain high values of coercivity and increased thermal stability. To overcome this dependency on scarce materials, worldwide efforts to develop rare-earth lean/free permanent magnets is promoted. We studied the crystallization of melt-spun Dy-free NdFeB(Nb-Cu) alloys with Nd reduced 16-25wt% as a mean of optimizing their microstructure and magnetic properties for PM applications. We report the effect of infiltration treatments on the magnetic properties of such alloys. Experiments were carried out on Nd-Fe-B-(Nb-Cu) melt-spun ribbons with a wide composition range, using the low melting point Pr3(Co-Cu) eutectic alloy as the infiltration material. Best results of coercivity enhanced were obtained in samples with high content of α-Fe phase, reaching a maximum coercivity of 25 kOe, similar to that of Dy enriched alloys. Work supported by DOE-DE-FG02-90ER45413 and EU-Horizon2020-686056.

3:10 PM  
High Magnetic Field Processing of Melt-spun Permanent Magnet Alloys: Michael McGuire1; Orlando Rios1; Ben Conner1; William Carter1; Lin Zhou2; Brandt Jensen2; Kewei Sun2; Mianliang Huang2; Olena Palasyuk2; Kevin Dennis2; Ikenna Nlebedim2; 1Oak Ridge National Laboratory; 2The Ames Laboratory
    Melt-spinning provides an important source of powders for use in magnet manufacturing. In addition, this rapid solidification technique can generate “over quenched” materials that provide an ideal starting point for non-equilibrium processing studies. Here we discuss some recent results from our investigation of how high magnetic fields can affect the evolution of such materials during thermal processing in which the microstructure and hard magnet properties are developed. Results from both rare-earth magnet materials and Hf-Co-B alloys are presented. We find strong effects of the magnetic field on particle size and crystallinity as well as chemical phase selection during thermal annealing of the melt-spun materials. Our observations demonstrate thermo-magnetic processing provides additional control over key microstructural properties, and is a promising tool for enhancing magnetic performance of advanced permanent magnets.

3:30 PM Break

3:50 PM  
Structural Evolution in Alnico -- A Transmission Electron Microscopy and Atom Probe Tomography Study: Lin Zhou1; Wei Guo2; Jon Poplawsky2; Wei Tang1; Iver Anderson1; Matt Kramer1; 1Ames Lab; 2Oak Ridge National Laboratory, Center for Nanophase Materials Sciences
    Alnico magnetic properties are closely related to spinodal decomposition (SD) that produces Fe-Co based (α1 phase) hard magnetic phase and non-magnetic Ni-Al based phase (α2 phase) after extended magneto-thermal treatment: solutionizing/quenching, magnetic-field annealing for anisotropic growth of the SD phases, and draw annealing to optimize the magnetic properties. Improved performance of alnico requires better understanding between processing conditions and microstructure. We have demonstrated nearly a 2x increase of coercivity between magnetic annealing (MA) and MA with drawing. In order to understand the origin of increased coercivity, we performed a careful microstructure and magnetic property investigation on 32.4Fe-38.1Co-12.9Ni-7.3Al-6.4Ti-3.0Cu (at.%) alnico at different stages during MA and heat treatment. Atom probe tomography, orientation imaging microscopy, and transmission electron microscopy techniques were used to elucidate the structural and chemical evolution of the SD phases in the alnico alloy and their effect on magnetic properties. Supported by USDOE-EERE-VT-EDT through Ames Lab contract DE-AC02-07CH11358.

4:10 PM  
Powder-processed High-performance Alnico Magnets by Thermal Gradient Control: Emma White1; Aaron Kassen1; Wei Tang1; Matthew Kramer1; Iver Anderson1; 1Ames Laboratory
    Replacing rare earth magnets with alternatives, such as alnico, will eliminate supply instability, increase sustainability and decrease costs of permanent magnets for applications such as traction drive motors. Lack of useful coercivity in alnico magnets limits their application for traction drive motors, despite their high temperature stability. To achieve the best second quadrant squareness and energy product, directional solidification is used to produce aligned alnico magnets. The randomly oriented, fine-grained microstructure of powder-processed, sintered alnico magnets have inferior energy products and are used for lower energy applications. This work describes powder-processed high-performance alnico magnets using epitaxially seeded solid-state grain growth driven by thermal gradient control. A modified alnico 8 composition was high-pressure gas atomized, sintered to full density, and heat treated to achieve improved magnetic properties. These alnico magnets have been thoroughly characterized using SEM, EBSD, and hysteresigraph measurements. Work funded by USDOE-EERE-VT-EDT program through Ames Lab contract no. DE-AC02-07CH11358.

4:30 PM  
Reduced Cobalt Energy Efficient “Green” Alnico: Andriy Palasyuk1; Brandon Kiel2; Kevin Dennis1; Wei Tang1; Lin Zhou1; Aaron Kassen2; Emma White2; Mathew Kramer1; Iver Anderson1; 1Ames Laboratory; 2Iowa State University, DMSE
    The novel alloying concept of equi-electronic replacement of the critical element Co by more abundant Fe and Ni showed that the unique self-assembled spinodal nanostructure of alnico remains unchanged even when the total Co content is reduced by 45%. According to the Rigid Band Approximation this is due to minimal disruption in total electron concentration of the system, i.e. e/a ≈ constant, maintaining the electronic structure even after significant chemical modification. Application of equi-electronic Co-reduction saves not only critical material but significantly lowers the solution annealing temperature and other processing parameters, while preserving and/or significantly improving performance of alnico 8, e.g., magnetic coercivity. Depending on the amount of Co that is being reduced, the coercivity varies from ~1500Oe in magnets with 40-45% less Co to ~2500Oe in alloys with 15-20% of Co reduction. Supported by USDOE-EERE-VT-EDT, within the DREaM project at Ames Laboratory, operated by ISU under contract no. DE-AC02-07CH11358.

4:50 PM  Cancelled
Reconsidering Substitutions in Sr-Ferrite Magnets: Waleed Khalifa1; Omayma El-Kady2; 1Cairo University; 2CMRDI
    This work was carried out to investigate the effect of alloying substitutions of lanthanum, cobalt, aluminium and vanadium oxides in manufacturing Sr-M ferrite magnets. The work focused on the synthesis of the ferrite magnets via the ceramic processing method. The results showed that Sr-ferrites showed much higher coercivity compared with the Ba-ferrites (more than doubled), and little difference in retentivity. The ferrite magnets of SrO.6Fe2O3 and SrO.5Fe2O3 showed high coercivity and retentivity in the range of 4025 - 4038 G, and 32 – 34 emu/g, respectively. The optimum levels of La2O3 and CoO substitutions are in the level of 0.1 to 0.3 mole fractions with high improvements in both retentivity and coercivity. Higher additions deteriorated the magnetic properties. The effect of alumina and vanadium oxides are also studied and showed huge improvements in the coercivity of the Sr-ferrite magnets.

5:10 PM  
Synthesis and Processing of Hard Iron Oxide Nanocomposites for Rare Earth Free Permanent Magnets: Kyle Chan1; Yasuhiro Kodera1; Javier Garay1; 1University of California, San Diego
    While iron oxides have been known and studied for centuries, it is still a promising building block for permanent magnets for various reasons. Fe and O are extremely earth abundant, and thus are relatively inexpensive. Also, Iron (III) Oxide exists in various polymorphs which have an amazing range of magnetic properties. For example, the most stable phase, a-Fe¬2O3 is an antiferromagnet, metastable g-Fe2O3 is soft ferrimagnet andmetastbale g-Fe2O3 is a canted antiferromagnet that has a very large coercivity (up to 2 Tesla). We present results on the chemical synthesis of high coercivity iron oxide phases and the integration into a consolidated nanocomposite via Current Activated Pressure Assisted Densification (CAPAD). We will show that this synthesis/processing route can produce hard bulk magnets with coercive fields comparable to typical rare-earth magnets based primarily on iron oxides.