Manufacturing of Isotropic Bonded NdFeB Magnets from Gas Atomised Powders

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Escalada 3 BRUSSELS, OCTOBER 19 TH 2016 1 CEIT and Tecnun-University of Navarra, Pº Manuel Lardizábal 15, 20018 San

2 Manufacturing of Isotropic Bonded NdFeB Magnets from Gas Atomised Powders J. Pérez-Arbulu 1, N. Burgos 1, J.M. Martín 1, I. Elosegui 1, M. Martínez- Iturralde 1, G. Almandoz 2 and A. Escalada 3 BRUSSELS, OCTOBER 19 TH CEIT and Tecnun-University of Navarra, Pº Manuel Lardizábal 15, San Sebastián, Spain 2 Mondragon Unibertsitatea, Faculty of Engineering, Loramendi, 4, Arrasate-Mondragón, Spain 3 Orona Elevator Innovation Centre, Polígono Epele, Hernani, Spain

3 INTRODUCTION NdFeB magnets: Sintered Highest (BH) max. D. Goll and H. Kronmüller, High-performance permanent magnets, Naturwissenschaften, vol. 87, no. 10, pp , 2000

4 INTRODUCTION NdFeB magnets: Bonded: K. H. J. Buschow, Magnets: Bonded Permanent Magnets, in Encyclopedia of Materials: Science and Technology, Elsevier Science Ltd, 2002, pp. 1 5

INTRODUCTION NdFeB powders for bonded magnets: Melt spinning. Flake-like powder. D t 25-50 m, D w 100-200 m. G 50-200 nm. ρ 6.2 g/cm 3. X v-ndfeb 77.5 %. B r 0.657 T. H cb 447 ka/m. H cj 952 ka/m.

5 INTRODUCTION NdFeB powders for bonded magnets: Melt spinning. Flake-like powder. D t m, D w m. G nm. ρ 6.2 g/cm 3. X v-ndfeb 77.5 %. B r T. H cb 447 ka/m. H cj 952 ka/m. (BH) max 73 kj/m 3. Isotropic magnets. MQEP-14-12, high temperature, corrosion resistance Magnequench Technical Resource Website, [Online]. Available: [Accessed: 01-Jan-2015]

D10 60 m, D50 130 m, D90 200 m. G 300 nm. ρ 6.2 g/cm 3. B r 0.95 T. H cb 657 ka/m. H cj 1372 ka/m.

6 INTRODUCTION NdFeB powders for bonded magnets: Hydrogenation-disproportion-dehydrogenation-recombination (HDDR) process. Irregular powder. D10 60 m, D m, D m. G 300 nm. ρ 6.2 g/cm 3. B r 0.95 T. H cb 657 ka/m. H cj 1372 ka/m. (BH) max 155 kj/m 3. Anisotropic magnets. MF18C Magfine - The World s Strongest Bonded Magnet. [Online]. Available: [Accessed: 01-Jan-2015]

$INTRODUCTION NdFeB powders for bonded magnets: Gas atomisation. Spherical powder. Sieve fraction 20-25 m ( 12.5 %). G 1.5-2 m.$ (BH) max 46 kj/m 3. Isotropic magnets. No commercial powder I. E. Anderson, R. W. McCallum, and W.

(BH) max 46 kj/m 3. Isotropic magnets. No commercial powder I. E. Anderson, R. W. McCallum, and W.

7 INTRODUCTION NdFeB powders for bonded magnets: Gas atomisation. Spherical powder. Sieve fraction m ( 12.5 %). G m. Powder magnetic properties: B r 0.64 T. H cb --- ka/m. H cj 836 ka/m. (BH) max 76 kj/m 3. Magnet assuming X v-ndfeb 77.5 %. (BH) max 46 kj/m 3. Isotropic magnets. No commercial powder I. E. Anderson, R. W. McCallum, and W. Tang, Alloy design and microstructure of advanced permanent magnets using rapid solidification and powder processing, Int. J. Powder Metall. (Princeton, New Jersey), vol. 44, no. 6, pp , 2008

8 INTRODUCTION NdFeB powders for bonded magnets: Melt spinning. Hydrogenation-disproportion-dehydrogenationrecombination (HDDR) process. Gas atomization: Isotropic bonded magnets. Grain size of gas atomised NdFeB powders is roughly 5 times coarser than for HDDR powders and at least 10 times coarser than for melt spinning powders. Lower magnetic properties, but also lower cost when compared with the other methods. Objective: This work presents some preliminary results about the manufacturing of new bonded NdFeB magnets by compression moulding from gas atomised powders. 19/10/2016 EARPA FORMForum 8

EXPERIMENTAL PROCEDURE Fabricated by PSI Ltd UK Dual atomizer water & gas Two main chamber: Melt chamber Atomization chamber Induction melting Vacuum

9 EXPERIMENTAL PROCEDURE Fabricated by PSI Ltd UK Dual atomizer water & gas Two main chamber: Melt chamber Atomization chamber Induction melting Vacuum pump Powder collector Cyclone Gas atomization can be performed totally under inert conditions to get high-purity powders 19/10/2016 EARPA FORMForum 9

10 EXPERIMENTAL PROCEDURE Gas atomisation experiments: Convergent-divergent gas nozzle. Close-coupled with annular slot. Induction melting and atomisation under a high purity Ar atmosphere. Atomisation conditions: Batch size (g) Atom. gas Gas pressure (MPa) Melt chamber pressurization (kpa) Melt superheat (ºC) Melt stream diameter (mm) Gas/metal mass flow rate ratio 1602 He Liquidus temperature of the alloy: 1260ºC.

11 EXPERIMENTAL PROCEDURE Compression moulding: Characteristics of the polymers: Ref. Supplier Physical form T g T m ρ (ºC) (ºC) (g/cm 3 ) Epoxy EpoFix Struers Liquid ~ Epoxy Araldite AT1-1 Huntsman Powder PA6 Ref. AM Goodfellow Powder, μm (>5 μm, <50 μm) PA12 Ref. AM Goodfellow Powder, μm (>10 μm, <50 μm) EpoFix: Epoxy resin with two components, the prepolymer and the hardener. Aging stars when both components are mixed and is completed in about 12 h at room temperature. AT1-1: One-component epoxy resin that is aged by heating above 120ºC. The proportion of polymer in the compression moulding feedstock was 20 vol%.

12 Temperature (ºC) Pressure (MPa) Temperature (ºC) Pressure (MPa) EXPERIMENTAL PROCEDURE Compression moulding: Theoretical density of each mixture: g/cm 3. Magnetic powder: <20 μm (95 % of the powder). Condition: As-atomised and after annealing at 650, 700 or 750ºC/15 min. Compression moulding cycle: T mol 10 min P mol T mol 10 min P mol Temperature 100 Pressure Time (min) 20 0 Temperature 100 Pressure Time (min) Epoxy resin (thermoset) Polyamide (thermoplastic)

13 RESULTS AND DISCUSSION Atomisation: Loss of 1.2 wt% of rare earths (Nd, Pr, Dy and Tb). Enrichment in Al. Low oxygen content. Ref. Composition (wt%) Nd Pr Dy Tb Fe Co B Al Si Raw material 25.1 ± ± ± ± ± ± ± ± ±0.003 Powder ± ± ± ± ± ± ± ± ±0.007 Ref. Composition (wt%) Cr Cu Nb Ga Mn Mo Ni Raw material ± ± ± ± ± ± ±0.0003

14 RESULTS AND DISCUSSION Atomisation: Particle size distribution: D10= 1.5 µm, D50= 6 µm, D90= 14 µm. Apparent density: 2.25±0.08 g/cm 3. Tap density: 4.4±0.1 g/cm 3. He pycnometer density: 7.46±0.01 g/cm 3.

15 Intensity (a.u.) RESULTS AND DISCUSSION Atomisation: Microstructure. α-fe Nd-rich phase θ

16 RESULTS AND DISCUSSION Annealing: Microstructure. 650ºC 700ºC 750ºC

17 RESULTS AND DISCUSSION Compression moulding: Properties of the magnets bonded with EpoFix resin in different states. Moulding pressure and temperature were 800 MPa and 100ºC, respectively. ρ Condition X v-ndfeb (%) X v-polymer (%) X v-porosity (%) g/cm 3 %TD As-atomised Annealed 650ºC Annealed 700ºC Annealed 750ºC Condition HV5 (kg/mm 2 ) B r (T) H cb (ka/m) H cj (ka/m) (BH) max (kj/m 3 ) As-atomised Annealed 650ºC Annealed 700ºC Annealed 750ºC

18 RESULTS AND DISCUSSION Compression moulding: Properties of the magnets bonded with AT1-1 resin. Powder annealed at 700ºC for 15 min. P mol (MPa) T mol (ºC) ρ X v-ndfeb (%) X v-polymer (%) g/cm 3 %TD X v-porosity (%) P mol (MPa) T mol (ºC) HV5 (kg/mm 2 ) B r (T) H cb (ka/m) H cj (ka/m) (BH) max (kj/m 3 ) ± ± ± ± ±

19 RESULTS AND DISCUSSION Compression moulding: Properties of the magnets bonded with PA12. Powder annealed at 700ºC for 15 min. P mol (MPa) T mol (ºC) ρ X v-ndfeb (%) X v-polymer (%) g/cm 3 %TD X v-porosity (%) P mol (MPa) T mol (ºC) HV5 (kg/mm 2 ) B r (T) H cb (ka/m) H cj (ka/m) (BH) max (kj/m 3 ) ± ± ± ± Ref. Supplier Physical form T g T m ρ (ºC) (ºC) (g/cm 3 ) Powder, μm (>10 μm, PA12 Ref. AM Goodfellow <50 μm)

20 RESULTS AND DISCUSSION Compression moulding: Powder annealed at 700ºC for 15 min. Pol. P mol (MPa) T mol (ºC) ρ (%TD) HV5 (kg/mm 2 ) B r (T) H cb (ka/m) H cj (ka/m) (BH) max (kj/m 3 ) EpoFix ± AT ± PA ± PA ± /10/2016 EARPA FORMForum 20

21 CONCLUSIONS a) A NdFeB powder with D50 6 μm has been manufactured by atomisation with He. A loss of rare earths of 1.2 wt% occurred during melting, mainly due to the reaction of the melt with the alumina crucible. The oxygen content of the raw material and the powder are similar. b) When the particle size decreases, the solidification rate increases and the microstructure of the as-atomised powders varies from a cellular micrometric structure to an equiaxial nanometric/ amorphous structure. The main phase is Nd 2 Fe 14 B. c) Annealing the powder between 650 and 750ºC for 15 min improves the magnetic properties of the bonded magnets. This improvement is attributed to the crystallization of amorphous phases and the transformation of metastable phases into Nd 2 Fe 14 B. d) Using epoxy resin and polyamide as bonding polymer, the compression moulding conditions have been optimizes to produce bonded magnets with <3 vol% of porosity and ~80 vol% of NdFeB powder. 19/10/2016 EARPA FORMForum 21

22 Thank you very much for your attention J.M. Martín 19/10/2016 EARPA FORMForum 22

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