Ian BakerThayer School of Engineering, Dartmouth College, Hanover, NH

HIGH PERFORMANCE NiFe PERMANENT MAGNETICS FOR ELECTRIC MOTORS

Supported by Dartmouth College Irving Institute for Energy and Society

Collaborators/Participants

Thayer School of EngineeringIIES-funded: Cynthia Bundi, Elisa Giraso, Jonathan Bonilla Toledo

Xiaobin Guo, Nour B. Hayek, Rachel Osmundsen, Ty Teodori, Chao Yang,

INSA Lyon, Villeurbanne, FrancePatrice Chantrenne, Damien Fabrègue

Seoul National University, Seoul, South KoreaHeung Nam Han, Ju-Won Park

Dunarea de Jos University of Galati, Galaţi, RomaniaGheorghe Gurau

Oak Ridge National Laboratory, Oak Ridge, TN, U.S.AGerard M. Ludtka, Bart Murphy

Argonne National Laboratory, Lemont, IL, U.S.ASi Chen, Yang Ren

http://fenixmagnetics.com/history-of-magnets/

History of Permanent Magnets

Polymer-bonded Nd2Fe14B magnets have a significantly lower energy product due to the polymer matrix.

https://ozank.gitbooks.io/ee361/magnetic_circuits/permanent_magnets.html

Why do we need more powerful magnets?

High Angle Angular Dark Field (HAADF) image taken in a scanning transmission electron microscope showing the microstructure of an AlNiCo alloy. The colored images are X-ray fluorescence maps from the same region, which show the locations of the constituent elements. Courtesy Lin Zhou and Matthew J. Kramer. From “Fifty Materials That Make the World”, Ian Baker, Springer, 2018.

AlNiCo MagnetsAlNiCo magnets represent the first nanostructured engineered magnets. - it became possible to replace electromagnets with permanent magnets- led to their widespread use in applications such as electric motors, loudspeakers, electric guitar

pickups, microphones, sensors, and traveling wave tubes in microwave amplifiers.

Demand for High Performance Magnets

Demand increasing rapidly for wind turbine generators and motors in both electric/hybrid cars. Sm-Co and Nd-Fe-B magnets are generally used for such challenging applications. Toyota Prius uses 1 kg of Nd and a typical wind turbine generator uses 250 Kg of Nd.

The hexagonal crystal structure of SmCo5.

Technical Issues with Rare Earth Magnets

Sintered Nd2Fe14B - vulnerable to grain boundary corrosionsolution: nickel or copper/nickel plating or lacquer coating.

Sm-Co magnets - brittle, prone to chipping, fracture from thermal shock.

Societal Issues with Rare Earth Magnets

• Over 95% of REs produced in China• No US-owned manufacturers• RE mining - severe environmental degradation, particularly in China

- low-grade ores requires large amounts of both water and energy to process• Substantial price volatility of RE elements.

From “Electric vehicle traction motors without rare earth magnets”, J.D.Widmer, R. Martin and M. Kimiabeigi, Sustainable Materials and Technologies 3 (2015) 7-13

Per p

ound

Demand for RE magnets

In 2015, the market value for NdFeB magnets - $7 billionSm-Co magnets - $427 million.

NdFeB magnets expected annual growth rates of 9% through 2020 to a market value of $10.7 billion.

Sm-Co magnets expected annual growth of 4.3% to a market value of $529 million.

Comparison of the estimated maximum energy product (BH)max, density, density-compensated maximum energy product, and price per unit maximum energy product for several classes of permanent magnets. The following prices for magnets were used: ferrites - $12/kg; AlNiCo - $44/kg; Nd-Fe-B - $180; SmCo- $140; NiFe - $10/kg (a conservative estimate based on the price of Ni and Fe and cold-rolling/annealing); t-MnAl - $22/kg (estimate using powder processing followed by consolidation for t-MnAl). Note that the values for Nd2Fe14B and Sm-Co are for sintered magnets; polymer-bonded magnets typically have half the value for (BH)max.

Magnet (BH)max (MGOe) Density (kg/m3) (BH)max/Density

(KGOe3/kg) $/MGOe

Nd2Fe14B 45 7600 5.92 4 Sm-Co 30 8300 3.61 4.7 NiFe 40-64 [4-5] 8300 4.8-7.7 0.15-0.25

t-MnAl 12 5200 2.31 1.8 AlNiCo 6.0 7000 0.86 7.3 Ferrites 4.5 5000 0.90 2.6

Permanent Magnet costs

From Massalski, T., Murray, J.L., Bennett, L.H. and Baker, H. “Binary Alloy Phase Diagrams”, American Society for Metals, 1 (1986); 1086.

Fe-Ni phase diagram

c/a = 1.0036

Lattice parameter in both cases is ~0.359 nm

NiFe

Ordered NiFe (Tetrataenite) identified in meteorites, where it transformed from the high temp. f.c.c. phase over 1000s of years

Albertsen, J.F., Aydin, M. and Knudsen, J.M., “Mossbauer Effect Studies of Taenite Lamellae of an Iron Meteorite Cape York (III.A)”, Physica Scripta, 17 (1977); 467-472.

Albertsen, J.F., Jensen, G.B. and Knudsen, J.M., “Structure of Taenite in Two Iron Meteorites”, Nature, 273 (8) (1978); 453-454.

Clarke, R.S., “Tetrataenite – Ordered FeNi, a New Mineral in Meteorites”, American Mineralogist, 65 (1980); 624-630.

Nagata, T., “High Magnetic Coercivity of Meteorites Containing the Ordered FeNi (Tetrataenite) as the Major Ferromagnetic Constituent”, Journal of Geophysical Research, 88 (1983); A779-A784.

Poirier, E. F.E. Pinkerton, R. Kubic, R. K. Mishra, N. Bordeaux, A. Mubarok, L. H. Lewis, J. I. Goldstein, R. Skomski, and K. Barmak, “Intrinsic magnetic properties of L1o FeNi obtained from meteorite NWA 6259 E”, Journal of Applied Physics 117, 17E318 (2015).

Petersen, J.F., Aydin, M. and Knudsen, J.M., “Mossbauer Spectroscopy of an Ordered Phase (Superstructure of FeNi in an Iron Meteorite)”, Physics Letters, 62A (3) (1977); 192-194.

Rubin, A.E., “Euhedral Tetrataenite in Jelica Meteorite”, Mineralogical Magazine, 58 (1994); 215-221.Scott, E.R.D., “Identification of Clear Taenite in Meteorites as Ordered FeNi”, Nature, 281 (1979); 360-362.Scott, E.R.D. and Rajan, R.S., “Metallic Minerals, Thermal Histories and Parent Bodies of some Xenolithic,

Ordinary Chondrite Meteorites”, Geochimica et Cosmochimica Acta, 45 (1981); 53-67.

Successful attempts to produce NiFe terrestrially:

∙Annealing for 30 days at 300oC Ramasam et al., “Positron Annihilation Studies of Ordered and Disordered Ni3Fe and NiFeAlloys”, Physica Scripta, 23 (1981); 297-300.

∙ Irradiating with 1 MeV electrons while heating in a transmission electron microscope enhanced the disorder-to order (f.c.c. to L1o) transformation in very thin NiFe films Reuter et al., “Ordering in the Fe-Ni System under Electron Irradiation”, Metallurgical Transactions A, 20A (1989); 711-718. and Yang et al., “A Revision of the Fe-Ni Phase Diagram at Low Temperatures (<400°C)“, Journal of Phase Equilibria, 17 (6) (1996); 522-531.

∙ Irradiating with 1 MeV neutron in presence of a magnetic field at 295oC Pauleve et al., “Magnetization Curves of Fe-Ni (50-50) Single Crystals Ordered by Neutron Irradiation with an Applied Magnetic Field”, Journal of Applied Physics, 39 (2) (1968); 989-990.

(b)

(a)

-30 -20 -10 0 10 20 30

-1.0

-0.5

0.0

0.5

1.0 25Oe 50Oe 100Oe 200Oe 10Oe

Mr/M

s

Field (Oe)

-30 -20 -10 0 10 20 30

-1.0

-0.5

0.0

0.5

1.0

Field (Oe)M

r/Ms

5Oe 10Oe 25Oe 50Oe 100Oe 200Oe

Fig. 4 Field dependence of the hysteresis loops for (a) as sputtered, and (b) annealed at 280 oC FeNi films

“Magnetic Ordering of Sputtered Nanostructured Fe50Ni50 Films”, Q. Zeng, I. Baker and Y. Zhang, IEEE Transactions on Magnetics, 41(10) (2005) 3358-3360.

Sputtered Nanostructured Fe50Ni50 Films

for 1 weekAnnealed at 280oC for 1 week

No superlattice reflections observed

APPROACH

Heavily deform and anneal to recrystallize to L10 phase

EXPERIMENTAL

1. Cold roll (87% reduction) + 295oC/30 days ✕2. Cold roll at -200oC (87% reduction) + 275oC/30 days ✕3. Cold roll + 295oC anneal in 8.5T magnetic field. ✕4. Torsion (500-600% strain) + 295oC anneal ✔5. Cold roll + 295oC anneal using electrical current. ✔6. Cold Roll + Electro-pulsing at 300oC. ✔

Adapted from Y. Hayakawa, ”Mechanism of secondary recrystallization of Goss grains in grain-oriented electrical steel”, Sci Technol Adv Mater. 18 (2017):480-497.

Initial grain structure

Rolled grain structure

Recrystallized grain Structure after annealing

After of rolling and annealing on grain structure

“Discovery of process-induced tetragonality in equiatomic ferromagnetic FeNi”, A.M. Montes-Arango, L.G. Marshall, A.D. Fortes, N.C. Bordeaux, S. Langridge, K. Barmak, L.H. Lewis, Acta Materialia 116 (2016) 263-269

Prior Attempt

After processing disordered tetragonal phaseannealed

Assessed composition Processing

Fe54Ni46 cold-rolled

Fe52Ni46Ti2 cold-rolled

Fe49Ni50Ti1 cryomilled

Fe51Ni49 cold-rolled

Fe50Ni48Ti2 cold-rolled

Rietveld fitting of neutron diffraction data

Cold rolled at room temperature

Cold rolled at 77 K

From 34 mm to 4.5 mm, with 86.8% reduction

From 34 mm to 5 mm, with 85.3% reduction

Cold-rolled NiFe

Raw materials - 34 mm ht, 37 mm wide, 37 mm long

Orientation image of cold-rolled NiFe

XRD of cold-rolled NiFe

f.c.c (220)

(311)(111) (200)

Orientation image of NiFe annealed inconventional furnace for 7 h at 295oC

(111) (200)

(220)

(311)

f.c.c.

XRD of NiFe annealed in conventionalfurnace for 7 h at 295oC

Cold-rolled NiFe annealed for 7 h at 295oC

(a) Synchrotron XRD from cold-rolled NiFe annealed for 7 h at 295℃,(b) intensity vs. 2q from (a), and (c) enlargement of the low angle region in (b).

No superlattice reflections corresponding to L10 phase

NiFe annealed for 7 h at 295oC

295oC/30 days annealed of Cold rolled NiFe

(111) (200)

(220)

(311)

f.c.c.

-200oC cold rolled + annealed 275℃/30 days

-200oC cold rolled + annealed 500℃/24h

-200oC roll + anneal

-200oC roll + anneal-200oC rolled

-200oC roll + anneal

(111) (111)

(200)(200)

(220)

(220)(311)

(311)

(222) (222)

f.c.c f.c.c

-6000 -4000 -2000 0 2000 4000 6000-200

-150

-100

-50

0

50

100

150

200

cast annealed 77 K cold rolled

Mom

ent (

emu/

g)

Field(G)

Magnetic Properties of NiFe

NiFe annealed 295oC for 4.5 h in 8.5 T magnetic field

Cold-rolled NiFe Annealed in 8.5 T magnetic field for 4.5 h at 295oC

(220)

(200)(111) (311)

f.c.c

Torsion + furnace annealed for 30 days/295℃

20 40 60 80 100 1200

15003000450060007500

ORNL

20 40 60 80 100 120

0

500

1000

1500

Inte

nsity

(Cou

nts)

Romania

20 40 60 80 100 120

0

500

1000

2Q

77KCR-Annealed

(111) (200)

(220)

(311) (222)

Magnetic annealed

Torsion - annealed

Recrystallized

-6000 -3000 0 3000 6000

-180

-120

-60

0

60

120

180

ORNL annealed Romanian Annealed 77K cold rolled+295 C/30 days Annealed

Mag

netic

Mom

ent (

emu/

g)

Field(G)

Magnetic fieldtorsion

Processing conditions Annealing conditions Magnetic

(emu/g)

Cast 133.3 ± 7

Cold rolled at 77 K Annealed in furnace for 30 days at 295oC 150.0 ± 5

Torsion 150.4 ± 4

Temperature in middle of sample and currentdensity during anneal using an electric current.

temperature

Current density

Schematic of the set-up for electricalheating of the NiFe showing theposition of the thermocouple.

Electrical current annealing of NiFe

Electric current: 1 A/mm2

Orientation image of NiFeannealed for 7 h at 295oC via electrical heating

Electrical current annealing of NiFe

(111)

(200)

(220)(311)

XRD of NiFe annealed for 7 h at 295oC via electrical heating

(a) Synchrotron XRD from cold-rolled NiFe electrically heated to 290℃ for 7 h,(b) intensity vs. 2q plot from (a), and (c) enlargement of the low angle region in (b).

Only f.c.c.

No superlattice reflections

3000 6000 9000

80

120

160 ORNL annealed 77K cold rolled Quenched Cast Romanian Annealed Lyon Annealed Cold rolled 77K cold rolled+Annealed

Mag

netic

Mom

ent (

emu/

g)

Field(G)

0 50 100 150 200 250 300

Vickers Hardness (HV)

resistivity: 75-85 x10-8 ohm·mThermal conductivity: 12-15 W/m·KSpecific heat: 505-525 J/kg·KDensity: 8.1-8.2 kg/m3

http://www.nickel-alloys.net/invar_nickel_iron_alloy.html#_Physical_properties

20 mm10 mm

1 mm

Fe-Ni as-received specimen

EBSD analysis (using γ, α phase)Fe-Ni phase diagram(both stable and metastable phase) IPF map KAM map

Misorientation angle: 15o

ND

RD

TD

γ1: low-Ni paramagnetic fccγ2: high-Ni ferromagnetic fcc

γ’: ordered FeNi3

γ’’: ordered FeNi

Ref) R.B. Scorzelli, Hyperfine Interactions 110 (1997)

300oC - 30 min continuous DC treatment

Electric current: 15 A/mm2 (230 A)

Misorientation angle: 15o

ND

RD

TD

0 500 1000 1500 20000

100

200

300

400

Tem

pera

ture

(o C)

Time (sec)

IPF map KAM map

EBSD analysis (using γ, α phase)

300oC - 30 min pulsed DC treatment

Electric current: 100 A/mm2 (1500 A), td= 0.1 s, tp= 5 s

0 500 1000 1500 20000

100

200

300

400

Tem

pera

ture

(o C)

Time (sec)

Misorientation angle: 15o

ND

RD

TD

IPF map KAM map

EBSD analysis (using γ, α phase)

X 500 X 1500

300oC - 30 min pulsed DC treatment

Electric current: 100 A/mm2 (1500 A), td= 0.1 s, tp= 5 s

Misorientation angle: 15o

ND

RD

TD

Hardness analysis

As-received CDC PDC200

250

300

350

Vick

ers

hard

ness

(HV)

CDC: continuous direct currentPDC: pulsed direct current

77 K rolled

As cast hardness 122 HV

Conclusions

1. Cold roll (RT or -200oC) + anneal at 295oC for 30 days

not recrystallized

1. Cold roll + anneal for 4.5 h at 295oC in 8.5 T magnetic field not recrystallized

2. Torsion + annealing at 295oC for 30 days recrystallization, but still f.c.c.

3. Cold roll + electrical anneal at 295oC for 7 h recrystallization, but still f.c.c. phase

4. Cold roll + electro-pulse anneal at 300oC for 30 min recrystallization – still being investigated

Next• XRD and magnetic measurements on electro-

pulse anneals specimens• Study martensitic transformation in NiFe-C• Add ternary or quaternary elements to raise

transformation temperature –Q-M calculations

0.0

0.1

0.2

0.3

0.4

0.5

100 200 300 400 500A

rea

Frac

tion

Grain Size (Diameter) [microns]

Grain Size (diameter)

-200oC cold rolled + annealed 275℃/30 days

-200oC cold rolled + annealed 500℃/24h

-200oC roll + anneal

-200oC cold rolled + annealed 275℃/30 days

-200oC cold rolled + annealed 500℃/24h

-200oC rolled and annealed

Torsion + annealed in furnace for 30 days at 295℃

1 2 3 4 5 60

50

100

150

200

250

300

295C

/30d

ann

eale

d of

tors

ion

Ann

eale

d in

mag

netic

fiel

d at

295

C

295C

/30d

ann

eale

d of

CR

Rom

ania

n To

rsio

n

77K

Col

d ro

lled

Vick

er H

ardn

ess

(HV)

Col

d ro

lled

Conditions

Hardness

Processing conditions Annealing conditions Hardness

(HV)

Cold rolled 223 ± 10

Cold rolled at 77 K 246 ± 5

Torsion 189 ± 7

Cold rolled 252 ± 2

Cold rolled 262 ± 3

Torsion 270 ± 4

-6000 -3000 0 3000 6000

-180

-120

-60

0

60

120

180 ORNL annealed 77K cold rolled Quenched Cast Romanian Annealed Lyon Annealed Cold rolled 77K cold rolled+Annealed

Mag

netic

Mom

ent (

emu/

g)

Field(G)

I100 a (fNi - fFe)2 = (28 – 26)2 = 1.4 x 10-3

I200 (fNi + fFe)2 (28 + 26)2

Intensity of X-ray peaks for L10 NiFe

Ratio of superlattice to fundamental peak intensity

Difficult to see superlattice peaks with conventional X-ray set