Nd-Fe-B Permanent Magnets
1
EXPLORING RESOURCE EFFICIENT PRODUCTION ROUTES FOR Nd-Fe-B PERMANENT MAGNETS Stefan Riegg 1* , Corinna Müller 1 , Fansun Chi 2 , Enrico Bruder 3 , Franziska Staab 3 , Peter Groche 2 , Clemens Müller 3 , Karsten Durst 3 and Oliver Gutfleisch 1 1 Functional Materials, Materials- and Geoscience, Technical University Darmstadt, 64287 Darmstadt, Germany 2 Institute PtU, Mechanical Engineering, Technical University Darmstadt, 64287 Darmstadt, Germany 3 Physical Metallurgy, Materials- and Geoscience, Technical University Darmstadt, 64287 Darmstadt, Germany * Corresponding author. e-mail: [email protected] Nd-Fe-B cast material 10 μm 10 μm Nd-Fe-B sintered magnet Crushing Milling Aligning Pressing Sintering Sintering route 10 μm Nd-Fe-B after swaging Rotary swaging Deformation by rotary swaging Nd-Fe-B Permanent Magnets Strip Casting Process Rotary Swaging Nd-Fe-B magnets base on the excellent intrinsic magnetic properties of Nd 2 Fe 14 B. Transformed to a key microstructure, remanences of up to 1.4 T and energy densities of more than 400 KJ/m 3 can be achieved in sintered magnets, which have the greatest market share (based on $) since more than 10 years. The production of a typical annual amount of 150.000 tons/year is increasing due to the increasing demand by e-mobility, robotics and energy conversion applications. The magnets possess a high resource criticality by two main reasons, one third of the weight is composed of rare-earth metals (Nd, Pr, Dy, Tb) and the complex production from the ore to the magnet consumes a lot of energy, water and chemicals. O. Gutfleisch, M.A. Willard, E. Brück, C.H. Chen, S.G. Sankar, J.P. Liu, Magnetic Materials and Devices for the 21st Century: Stronger, Lighter, and More Energy Efficient, Advanced Materials 23, 821-842 (2011) Element production (mining, refining,…) Melting, Casting, Crushing Aligning Powder Hydrogen decrepitation Jet Milling Pressing Sintering, Annealing Shaping, Machining, Coating Magnetizing In the powdermetallurgical process route for sintered magnets typically the starting materials are strip cast flakes. The microstucture and phase composition obtained by this rapid cooling technique has strong impact on the achievable magnet grade of the final sintered product. Thus the composition (Nd,Fe,B + Pr,Dy,Co,Al,Ga,…) as well as the casting conditions (temperature, speed of tilting, wheel rotation speed) provide a large parameter space to optimize process and material. The targeted smaller grain size in the sintered magnet leads to an increased coercivity and allows to reduce the amount of heavy rare earth elements (Dy,Tb). The adaption of composition and process condition allows to reach a coercivity of 2000 kA/m at room temperature and an improved high temperature (200°C) performance although the amount of Dy by more than 1.5wt%. This work and the upscaling to a commercial production are the goals of the EIT Raw Materials funded project „UPGRADE“ running from 2019 – 2021 A top down approach is used in the project funded by the Pioneer Fund of TU Darmstadt. This means, a cast rod of Nd-Fe-B material is wrapped with a steel cladding and the existing coarse Nd-Fe-B grains are broken down to few micrometer size by a rotary swaging step. Before swaging, the rod is preheated to reach the thixo-state of a partly molten material. This is possible, since the grain boundary phase of the Nd-Fe-B magnet already melts below 700°C. The crushing is supported by a flow of this liquid material to the opening cracks forming ideally a fine grained structure similar to a sintered magnet. With this method the several process steps can be combined in just one bulk process. In addition, this route is promising for a continuous production compared to the typical state of the art batch production. However, the application of these magnets is limited being isotropic magnetic material with rod-like shapes. K. Löwe, D. Benke, C. Kübel, T. Lienig, K. Skokov und O. Gutfleisch, Acta Materialia 124, 421 (2017) Typical Nd-Fe-B sintered magnet microstructure 5 μm Nd 2 Fe 14 B Nd-rich grain boundary phase Pre-alloy production Powder-metallurgy Post processing Process chain of the state of the art sintered magnet production Gauß R., Gutfleisch O., Magnetische Materialien - Schlüsselkomponenten für neue Energietechnologien. In: Kausch P., Matschullat J., Bertau M., Mischo H. (eds) Rohstoffwirtschaft und gesellschaftliche Entwicklung. Springer Spektrum, Berlin, Heidelberg, (2016) S. Shaw, S. Constantinides, Permanent Magnets: The Demand for Rare earths. 8th International Rare Earths Conference (2012) F. Chi, L. Wießner, T. Gröb, E. Bruder, S. Sawatzki, K. Löwe, J. Gassmann, C. Müller, K. Durst, O. Gutfleisch, P. Groche Towards manufacturing of Nd-Fe-B magnets by continuous rotary swaging of cast alloy, Journal of Magnetism and Magnetic Materials, 165405 (2019) P. Groche, F. Chi, L. Wießner, T. Gröb, E. Bruder, C. Müller, Method for producing a permanent magnet or a hard magnetic material, Patent: WO2019170593A1 Casting Swaging Shaping Magnetization Targeted region Taken from: K. Yamamoto, R. Murakami, Microstructure Formation on NdFeB Ternary Alloy System for Magnet by Strip Casting Method, J. Japan Inst. Met. Mater. 80, 1 (2015) Scanning Electron Microscopy picture of cross section of a strip cast flake, the lamellar structure is formed by Nd 2 Fe 14 B (dark) and Nd-rich grain- boundary phase (light) J. Fidler und T. Schrefl, „Overview of Nd-Fe-B magnets and coercivity (invited),“ IEEE Trans. Magn. 79, 5029 (1996) Uestuener, K., Katter, M., and Rodewald,W., “Dependence of the mean grain size and coercivity of sintered nd–fe–b magnets on the initial powder particle size,” IEEE Transactions on Magnetics 42, 2897–2899 (2006) Roll side Nucleation site Details of the microstructure by optical microscopy - Intersection method to obtain lamellar thickness values
Transcript of Nd-Fe-B Permanent Magnets
EXPLORING RESOURCE EFFICIENT PRODUCTION ROUTES
FOR Nd-Fe-B PERMANENT MAGNETS
Stefan Riegg1*, Corinna Müller1, Fansun Chi2, Enrico Bruder3, Franziska Staab3,
Peter Groche2, Clemens Müller3, Karsten Durst3 and Oliver Gutfleisch1
1 Functional Materials, Materials- and Geoscience, Technical University Darmstadt, 64287 Darmstadt, Germany
2 Institute PtU, Mechanical Engineering, Technical University Darmstadt, 64287 Darmstadt, Germany
3 Physical Metallurgy, Materials- and Geoscience, Technical University Darmstadt, 64287 Darmstadt, Germany
* Corresponding author. e-mail: [email protected]
Nd-Fe-B cast material
10 μm
10 μm
Nd-Fe-B sintered magnet
Crushing
Milling
Aligning
Pressing
Sintering
Sintering route
10 μm
Nd-Fe-B after swagingRotary swaging
Deformation by rotary swaging
Nd-Fe-B Permanent Magnets
Strip Casting Process Rotary Swaging
Nd-Fe-B magnets base on the excellent intrinsicmagnetic properties of Nd2Fe14B. Transformed to akey microstructure, remanences of up to 1.4 T andenergy densities of more than 400 KJ/m3 can beachieved in sintered magnets, which have thegreatest market share (based on $) since morethan 10 years.
The production of a typical annual amount of 150.000 tons/year is increasing due to the increasingdemand by e-mobility, robotics and energy conversion applications. The magnets possess a high resourcecriticality by two main reasons, one third of the weight is composed of rare-earth metals (Nd, Pr, Dy, Tb)and the complex production from the ore to the magnet consumes a lot of energy, water and chemicals.
O. Gutfleisch, M.A. Willard, E. Brück, C.H. Chen, S.G. Sankar, J.P. Liu, Magnetic Materials and Devices for the 21st Century: Stronger, Lighter, and More Energy Efficient, Advanced Materials 23, 821-842 (2011)
Element production (mining, refining,…)
Melting, Casting, Crushing
Aligning Powder
Hydrogen decrepitation
Jet Milling
Pressing
Sintering, Annealing Shaping, Machining, Coating
Magnetizing
In the powdermetallurgical process route forsintered magnets typically the startingmaterials are strip cast flakes. Themicrostucture and phase compositionobtained by this rapid cooling technique hasstrong impact on the achievable magnetgrade of the final sintered product.
Thus the composition (Nd,Fe,B + Pr,Dy,Co,Al,Ga,…) as well as the castingconditions (temperature, speed of tilting, wheel rotation speed) provide a largeparameter space to optimize process and material. The targeted smaller grainsize in the sintered magnet leads to an increased coercivity and allows toreduce the amount of heavy rare earth elements (Dy,Tb).
The adaption of composition and process condition allowsto reach a coercivity of 2000 kA/m at room temperatureand an improved high temperature (200°C) performancealthough the amount of Dy by more than 1.5wt%. Thiswork and the upscaling to a commercial production arethe goals of the EIT Raw Materials funded project„UPGRADE“ running from 2019 – 2021
A top down approach is used in the project funded by the Pioneer Fund of TUDarmstadt. This means, a cast rod of Nd-Fe-B material is wrapped with a steelcladding and the existing coarse Nd-Fe-B grains are broken down to fewmicrometer size by a rotary swaging step. Before swaging, the rod is preheatedto reach the thixo-state of a partly molten material. This is possible, since thegrain boundary phase of the Nd-Fe-B magnet already melts below 700°C. Thecrushing is supported by a flow of this liquid material to the opening cracksforming ideally a fine grained structure similar to a sintered magnet.
With this method the several process steps can be combined in just one bulkprocess. In addition, this route is promising for a continuous productioncompared to the typical state of the art batch production. However, theapplication of these magnets is limited being isotropic magnetic material withrod-like shapes.
K. Löwe, D. Benke, C. Kübel, T. Lienig, K. Skokov und O. Gutfleisch, Acta Materialia124, 421 (2017)
Typical Nd-Fe-B sinteredmagnet microstructure
5 µm
Nd2Fe14B
Nd-rich grain boundary phase
Pre-alloyproduction
Powder-metallurgy
Post processing
Process chain of the stateof the art sintered magnetproduction
Gauß R., Gutfleisch O., Magnetische Materialien -Schlüsselkomponenten für neueEnergietechnologien. In: Kausch P., MatschullatJ., Bertau M., Mischo H. (eds) Rohstoffwirtschaftund gesellschaftliche Entwicklung. Springer Spektrum, Berlin, Heidelberg, (2016)
S. Shaw, S. Constantinides, Permanent Magnets: The Demand for Rare earths. 8th International Rare Earths Conference (2012)
F. Chi, L. Wießner, T. Gröb, E. Bruder, S. Sawatzki, K. Löwe, J. Gassmann, C. Müller, K. Durst, O. Gutfleisch, P. GrocheTowards manufacturing of Nd-Fe-B magnets by continuous rotary swaging of cast alloy, Journal of Magnetism and Magnetic Materials, 165405 (2019)
P. Groche, F. Chi, L. Wießner, T. Gröb, E. Bruder, C. Müller, Method for producing a permanent magnet or a hard magnetic material,Patent: WO2019170593A1
Casting Swaging Shaping Magnetization
Targeted region
Taken from: K. Yamamoto, R. Murakami, Microstructure Formation on NdFeB Ternary Alloy System for Magnet by Strip Casting Method, J. Japan Inst. Met. Mater. 80, 1 (2015)
Scanning Electron Microscopy pictureof cross section of a strip cast flake, thelamellar structure is formed byNd2Fe14B (dark) and Nd-rich grain-boundary phase (light)
J. Fidler und T. Schrefl, „Overview of Nd-Fe-B magnets and coercivity (invited),“ IEEE Trans. Magn. 79, 5029 (1996)
Uestuener, K., Katter, M., and Rodewald,W., “Dependence of the mean grain size and coercivity of sintered nd–fe–b magnets on the initial powder particle size,” IEEE Transactions on Magnetics 42, 2897–2899 (2006)
Roll side
Nucleation site
Details of the microstructure by opticalmicroscopy - Intersection method toobtain lamellar thickness values
oborny
Stempel
