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 2016 1 CEIT and Tecnun-University of Navarra, Pº Manuel Lardizábal 15, 20018 San Sebastián, Spain 2 Mondragon Unibertsitatea, Faculty of Engineering, Loramendi, 4, 20500 Arrasate-Mondragón, Spain 3 Orona Elevator Innovation Centre, Polígono Epele, 20120 Hernani, Spain
INTRODUCTION NdFeB magnets: Sintered Highest (BH) max. D. Goll and H. Kronmüller, High-performance permanent magnets, Naturwissenschaften, vol. 87, no. 10, pp. 423 438, 2000
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. (BH) max 73 kj/m 3. Isotropic magnets. MQEP-14-12, high temperature, corrosion resistance Magnequench Technical Resource Website, 2010. [Online]. Available: http://www.mqitechnology.com/index.jsp. [Accessed: 01-Jan-2015]
INTRODUCTION NdFeB powders for bonded magnets: Hydrogenation-disproportion-dehydrogenation-recombination (HDDR) process. Irregular powder. 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. (BH) max 155 kj/m 3. Anisotropic magnets. MF18C Magfine - The World s Strongest Bonded Magnet. [Online]. Available: http://www.magfine.com/. [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. 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. 19 37, 2008
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 pump Powder collector Cyclone Gas atomization can be performed totally under inert conditions to get high-purity powders 19/10/2016 EARPA FORMForum 9
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 6.8 45 437 2.5 2.3 Liquidus temperature of the alloy: 1260ºC.
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 ~60-80 1.1 Epoxy Araldite AT1-1 Huntsman Powder 100-130 1.2-1.3 PA6 Ref. AM306010 Goodfellow Powder, 15-20 μm (>5 μm, <50 μm) 47 215 1.15 PA12 Ref. AM376010 Goodfellow Powder, 25-30 μm (>10 μm, <50 μm) 50 185 1.02 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%.
Temperature (ºC) Pressure (MPa) Temperature (ºC) Pressure (MPa) EXPERIMENTAL PROCEDURE Compression moulding: Theoretical density of each mixture: 6.17-6.20 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: 120 100 T mol 10 min P mol 700 600 120 100 T mol 10 min P mol 700 600 80 60 40 500 400 300 200 80 60 40 500 400 300 200 20 0 Temperature 100 Pressure 0 0 10 20 30 40 Time (min) 20 0 Temperature 100 Pressure 0 0 10 20 30 40 Time (min) Epoxy resin (thermoset) Polyamide (thermoplastic)
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 ±0.1 3.88 ±0.01 0.425 ±0.004 0.265 ±0.001 66.2 ±0.6 0.951 ±0.016 1.0141 0.365 ±0.0004 ±0.001 0.049 ±0.003 Powder 24.10 ±0.01 3.61 ±0.01 0.474 ±0.001 0.242 ±0.001 66.27 ±0.01 0.986 ±0.002 0.99 ±0.01 0.642 ±0.004 0.087 ±0.007 Ref. Composition (wt%) Cr Cu Nb Ga Mn Mo Ni Raw material 0.0155 ±0.0002 0.122 ±0.000 0.099 ±0.002 0.117 ±0.001 0.0418 ±0.0005 0.0265 ±0.0001 0.0090 ±0.0003
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.
Intensity (a.u.) RESULTS AND DISCUSSION Atomisation: Microstructure. α-fe 2500 2000 1500 1000 Nd-rich phase 500 0 20 30 40 50 60 70 80 2θ
RESULTS AND DISCUSSION Annealing: Microstructure. 650ºC 700ºC 750ºC
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 5.94 96 77 19 4 Annealed 650ºC 5.84 94 75 19 6 Annealed 700ºC 5.88 95 76 19 5 Annealed 750ºC 5.85 95 76 19 5 Condition HV5 (kg/mm 2 ) B r (T) H cb (ka/m) H cj (ka/m) (BH) max (kj/m 3 ) As-atomised - 0.41 210 595 22 Annealed 650ºC - 0.501 258 562 35 Annealed 700ºC - 0.501 260 530 36 Annealed 750ºC - 0.484 234 420 32
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) 800 100 800 200 ρ X v-ndfeb (%) X v-polymer (%) g/cm 3 %TD X v-porosity (%) 5.86 95 76 19 5 5.85 95 76 19 5 6.09 98 79 20 1 6.11 99 79 20 1 800 300 6.17 100 80 20 0 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 ) 800 100 800 200 102 ±24 0.489 234 471 31 111 ±12 0.479 230 472 30 121 ±24 0.496 220 430 30 135 ±13 0.500 219 427 30 800 300 148 ±20 0.505 214 403 30
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 (%) 200 210 5.63 91 73 18 9 400 210 5.97 96 77 19 4 600 210 5.95 96 77 19 4 600 250 6.01 97 78 19 3 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 ) 200 210 16 ±2 - - - - 400 210 21 ±3 0.482 216 465 27 600 210 21 ±2 0.483 220 473 28 600 250 21 ±3 0.487 219 471 28 Ref. Supplier Physical form T g T m ρ (ºC) (ºC) (g/cm 3 ) Powder, 25-30 μm (>10 μm, PA12 Ref. AM376010 Goodfellow <50 μm) 50 185 1.02
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 800 100 97 98 ±8 0.497 234 469 32 AT1-1 800 200 99 135 ±13 0.500 219 427 30 PA6 800 300 98 69 ±8 0.504 204 376 28 PA12 400 210 96 21 ±3 0.482 216 465 27 19/10/2016 EARPA FORMForum 20
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
Thank you very much for your attention J.M. Martín (jmmartin@ceit.es) 19/10/2016 EARPA FORMForum 22