Advanced Magnetic Materials for Energy and Power Conversion Applications: High-energy Product Permanent Magnets
Sponsored by: TMS Functional Materials Division, TMS: Magnetic Materials Committee
Program Organizers: Daniel Salazar, BCMaterials; Alex Leary, NASA Glenn Research Center; Markus Chmielus, University of Pittsburgh; Ryan Ott, Ames Laboratory; Arcady Zhukov, University of the Basque Country
Tuesday 8:30 AM
February 25, 2020
Room: Del Mar
Location: Marriott Marquis Hotel
Session Chair: Matthew Kramer, AMES Laboratory; Alberto Bollero, IMDEA Nanociencia
8:30 AM Invited
Controlling and Describing Coercivity of Rare Earth Permanent Magnets: Satoshi Hirosawa1; 1National Institute for Materials Science
Controlling coercivity and its temperature dependence has been the central issue in recent developments of high-performance rare earth permanent magnets. Manipulation of distribution profiles of constituent elements in fine-grained magnets utilizing subtle differences among chemical potentials of elemental species has become important in controlling coercivity in processes such as grain boundary diffusion or infiltration. However, even after decades of investigations, many aspects concerning thermodynamic (meta)stability and factors limiting achievable coercivity of the Nd2Fe14B-based magnets remain unexplained. The situation is more so for recently revisited 1-12-type magnets. Describing coercivity of the deliberately complex microstructure is still difficult and theoretical calculations of the effects of temperature and local magnetic fluctuations are on the way of developments. This talk will summarize some of recent progresses in the above mentioned topics.
9:00 AM Invited
Computational Design of Bulk Permanent Magnets: Thomas Schrefl1; Johann Fischbacher1; Alexander Kovacs1; 1Danube University Krems
With modern production technologies of permanent magnets such as additive manufacturing or grain boundary diffusion, the coercivity field can be adapted locally. In many applications, partial demagnetization reduces the performance of the magnet with increasing operating time. We combine magnetostatic field computation, micromagnetics and machine learning to identify regions where the local coercive field needs to be strengthened. We calculate energy barriers for magnetization reversal at different locations within the magnet, taking into account the distribution of the magnetostatic field. As a result, we obtain a map of the cumulative operating time before demagnetization. For example, in an external field of 0.8 T/μ0 at 300 K, a Nd2Fe14B magnet of 2x2x0.4cm3 demagnetizes after 1230 hours near the edge. At 450 K edge demagnetization occurs within a few minutes in an external field of 50 mT/μ0. The simulation of local magnetization reversal events guides the design of permanent magnets.
9:30 AM
Effects of Grain Size on Magnetic and Mechanical Properties of NdFeB Sintered Magnets: Wei Tang1; Gaoyuan Ouyang1; Baozhi Cui1; Matt Kramer1; Jun Cui2; Iver Anderson1; 1Ames Lab; 2Iowa State University
High-efficiency electric drive permanent magnet motors with exceptional powder density require the permanent magnets to have high magnetic and mechanical properties, thermal stability and low cost. Currently, Nd2Fe14B-based sintered magnets are one of the promising candidates if heavy rare earth (HRE)-free magnets with high coercivity (HC) and mechanical properties are well achieved. In this work, the effect of grain size on HC and mechanical strength of Dy-free NdFeB sintered magnets was fully studied. Three sintered magnet I, II and III were made respectively by the powders with three different particle sizes under the same sintering and heat treatment conditions. Magnet I, II and III obtained an intrinsic HC of 10.1, 11.3 and 9.1 kOe, respectively. The average flexure strength of magnet I, II and III is 262, 211 and 234 MPa, respectively. These results show that the HC increases but the flexure strength decreases with reduction of grain size.
9:50 AM
Mechanically Strengthened Heterogeneous Sm-Co Sintered Magnets: Baozhi Cui1; Jun Cui1; 1Ames Laboratory
SmCo5 and Sm2Co17 type sintered magnets have been widely used in telecommunication, sensors, power and propulsion applications, especially, at elevated temperatures of 200 - 550 oC. However, while Sm-Co sintered magnets possess excellent magnetic properties, they are brittle and impossible for applications subjected to high stress and vibration. The brittleness also leads to magnet production loss up to 30%. Improving the flexural strength or fracture toughness of Sm-Co magnets is of a great scientific, technical and practical significance. This presentation will discuss the strengthening strategies of effective enhancement of mechanical strength of the sintered Sm-Co magnets. As a typical case, our work showed that flexural strength values of Sm2(CoFeCuZr)17 sintered magnets were enhanced by up to about 50-100% while the excellent hard magnetic properties were maintained. The formation mechanism of the novel heterogeneous microstructure and its strengthening mechanism in the Sm-Co sintered magnets will be discussed.
10:10 AM Break
10:30 AM Invited
Application of Systems Level Modeling for Addressing Criticality in Rare Earth Magnets: Ikenna Nlebedim1; 1Ames Laboratory
In this talk, we will present the use of system levels modeling (SLM) for addressing rare-earth elements (REEs) supply challenges for permanent magnets (PMs) applications. PMs enable applications like energy-supplies, national-security, transportation, automation and personal devices. However, the geographical distribution of REEs poses a challenge for sustainable development and use of PMs. SLM tools like finite element analysis can help address such challenge by providing a virtual testbed for determining the actual performance required of PM in a system. SLM can help to determine when coercivity is more important than remanence or when mechanical-robustness is more crucial than weight/size by couple different physics for an application. Via such approach, we have predicted and experimentally validated that low field is required for aligning anisotropic bonded Nd-Fe-B magnets. We have shown the economic impact of replacing Nd-Fe-B with Sm-Co in wind energy applications. This talk will cover other such applications of SLM.
11:00 AM Invited
Additive Manufacturing of Hard Magnets for Tailored Magnetic Fields: Christian Huber1; Martin Groenefeld2; Dieter Suess1; 1University of Vienna; Christian Doppler Laboratory for Advanced Magnetic Sensing and Materials; 2Magnetfabrik Bonn GmbH
Additive manufacturing (AM) has the potential to realize complex geometries which would not be possible with conventional tooling technologies. Within this talk, I will give a review of several AM methods to print isotropic NdFeB and anisotropic ferrite magnets with complex shapes. The following AM methods will be presented: (i) Fused Deposition Modeling (FDM), (ii) Selective Laser Melting (SLM), and (iii) Stereolithography (SLA). Advantages and drawbacks of each method will be discussed on a complex magnetic system. Furthermore, I will present simulation techniques to design the topology and shape of magnetic structures for tailored magnetic fields. The simulated structures can be directly send to the AM system without an elaborate post processing.
11:30 AM
Anisotropy and Orbital Moment in Rare Earth - Cobalt Permanent Magnets: Durga Paudyal1; Renu Choudhary1; Ralph Skomski2; 1Ames Laboratory; 2University of Nebraska
Many features of Fe substituted R-Co systems are consistent with past research, but some are seemingly contradictory. The disagreement reflects how the many-electron nature of the rare-earth 4f electrons is interpreted by crystal-field and local spin density approximation with Hubbard model and spin-orbit-coupling (LSDA+U+SOC) theories. The two-sublattice crystal-field theory describes a broad variety of Sm-Co properties, such as the temperature dependence of magnetization and anisotropy, but it is not a first-principle approach. By contrast, our first-principle approach, LSDA+U, yields a substantial orbital-moment quenching, which violates Hund's rules and is contradictory to conventional knowledge accumulated over several decades of rare-earth research. Rationalizing the orbital-moment quenching in terms of the dependence of the 4f-charge distribution on the magnetization angle, we argue that medium- and long-run future research will be necessary to reconcile experiment, sublattice models, and first-principle calculations. This work is supported by the CMI.