Galfenol Technologies at ETREMA ProductsState‐of‐the‐Art & Future Direction

Eric Summers, VP & Chief Materials Engineer

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• Special thanks to ONR for their support of Galfenol Research

• Acknowledgements:• NSWC – Carderock, Magnetic Materials Group including Art Clark• Ames Laboratory, Dr. Tom Lograsso• Galfenol MURI members lead by Dr. Alison Flatau• Kanazawa University, Dr. Toshiyuki Ueno• All other researchers who have contributed to our body of knowledge

• Remember: Clark AE, Restorff JB, Wun‐Fogle M, Lograsso TA, Schlagel DL (2000) IEEE Trans Magn 36:3238

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Presentation Topics•Galfenol processing techniques•Properties• Future direction of Galfenol technology

•Galfenol technology roadmap•Commercialization ET

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Magnetostriction vs. Composition (single crystal)Fe1-xGa(0.15 ≤ x ≤ 0.20)

• ETREMA’s efforts have focused on the first magnetostrictive peak between 15 at% Ga and 20 at% Ga

• Galfenol alloys available at this compositional range

0 5 10 15 20 25 30 35 40

0

50

100

150

200

250

300

350

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450

3/2λ 1

00(x 10‐

6 )

x

Furnace CooledQuenchedDirectionally Solidified (Unannealed)Quenched in BrineFurnace Cooled, Multi‐phase

Fe100‐xGax

H = 15 kOe

Single crystal data courtesy of NSWC Carderock Magnetic Materials Group

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Galfenol Alloy Feedstock• Various feedstock alloys and shapes produced

• Bottom pour unit with 2 kg capacity – chill cast into various mold geometries

• Equipment limits capacity that can be produced

FSZM

Bridgman

Rolling Ingot

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Primary Production MethodAdvanced Bridgman Process• Directional solidification method

• Strong <100> texture• Primary composition = 18.4 at% Ga (nominal)• Other compositions around 1stpeak can be produced

• Typical geometry: 24 mm dia x 250 mm length

• Current equipment limits rod sizes that can be produced• Labor intensive

Photo of Galfenol being produced via Bridgman Process

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EBSD ComparisonAs‐Cast Feedstock Alloy Bridgman Rod

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Typical Quasi-static Curves• As‐grown Bridgman rod; Fe – 18.4 at% Ga nominal composition

Strain vs. Magnetic Field Flux Density vs. Magnetic Field

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Comparison to Terfenol-D• Less field required to reach

saturation• Larger pre‐stresses necessary

• Larger saturation flux density• Higher permeability• Less hysteresis

Strain vs. Magnetic Field Flux Density vs. Magnetic Field

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Galfenol PropertiesSaturation Strain 200 – 250 ppm at 48 MPa applied compressive load

Piezomagnetic Constant, d33 15 – 30 nm/A, lower values at larger stresses

Saturating Magnetic Field 100 – 250 Oe, value depends upon stress applied with larger stresses requiring high magnetic fields to reach saturation

Saturation Magnetic Flux Density 1.5 Tesla

Magnetic Permeability, μr 75 – 100, lower values at larger stresses

Coercivity, Hc 10 Oe

Hysteresis (major loop) 1000 J/m3

Curie Temp. ≈ 950 K

Density 7800 kg/m3

Hard Young’s Modulus 75 GPa

Soft Young’s Modulus ≈ 40 GPa

Tensile Strength ≈ 350 MPa

Elongation ≈ 1%

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• Typical properties of polycrystalline Galfenol (Fe81.6Ga18.4)• As‐grown material via Bridgman Process

Galfenol LaminationCritical Skin Depth w ith Frequency

100

1000

10000

100000

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5Critical Skin Depth, mm

Freq

uenc

y, H

z

Terfenol-DGalfenol

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Benefits• Mechanical robustness• High permeability

• efficient magnetic circuit• Low magnetic hysteresis

• ~10x less than Terfenol‐D

Disadvantages• Eddy current losses• Critical skin depth (20 kHz)

• δGalfenol = 0.38mm (0.015”)• δTerfenol = 1.23mm (0.048”)

• ¼ λsat

Material Permeability (μr)

Resistivity (ρ)

Galfenol 75-100 8.5x10-7 Ω·m

Terfenol 2-10 6.0x10-7 Ω·m

Galfenol Rolling• Viable high volume, low cost production method• Highly textured microstructure; (110)<001> RD (Goss)• Large grains• Large magnetostrictions measured in individual sheet samples; > 250 ppm

• Typical sheet dimensions: 11” length x 3” width x 0.014” thick• Investigating methods to produce thinner sheets

• Lab‐scale process – very labor intensive

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Rolled Sheet Stacks• Nominal Ga content: 18 at%

• Multi‐stage rolling to 0.36 mm (0.014”)

• Textured sheets via HT• Sample sectioning

• 10 mm x 15 mm• Laminated sheet stack assembly• 20 laminates/stack with ~35 µm (0.0015”) bond line 13

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RD

RD

TD ND

Stack Characterization

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λsat = 215 ppm

d33 = 20 nm/A

Msat = 1.3 Tµr = 85

Machining ExamplesGalfenol

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Welding & Forging

Laser welding courtesy of DRDC Atlantic

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Stress Annealing at ETREMA• Stress annealing process builds in a compressive stress into the Galfenol sample (referred to as an ‘uniaxial anisotropy’)• Result: full magnetostrictive performance without an extrinsic compressive stress applied

• Good magnetostrictive performance out into tension• Maximum built‐in stress achieved = 64 MPa

• Typical = 45 MPa

• Process can be tailored for a certain stress range• ETREMA has successfully stress annealed Galfenol alloys from 15 at% to 18.4 at% Ga• Including ternary alloys containing aluminum

• Current equipment limits length of a stress annealed specimen to 125 mm

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Galfenol in Tension

Test data courtesy NSWC – Carderock Magnetic Materials Group

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FUTURE DIRECTION OF GALFENOL TECHNOLOGY ETRE

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Magnetic Field Annealing• Magnetic field annealing (FA) processes under investigation at ETREMA• Results consistent with efforts accomplished under MURI

• Finalizing process parameters• Currently, small experimental setup available for field annealing samples• 6.35 mm dia x 50 mm length, typical FA geometry

3” x 3” x 6” chamber for FA

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Corner Stress Test Results

Test data courtesy NSWC – Carderock Magnetic Materials Group

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Field vs. Stress AnnealingStrain vs. Magnetic Field Flux Density vs. Magnetic Field

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Temperature Effects

FA sample, 200°C (not shown)‐755 hrs exposure, < 5% drop in λsat measured ET

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Elevated Temperature Properties• Inquiries into designing Galfenol actuators that can operate under extreme conditions; such as elevated temperature

• Magnetic property characterization at elevated temperatures• Quasi‐static testing up to 400°C• λ and B versus H, d33 and μr to be studied

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Fe-Ga-Al/Fe-Al Alloys• Reduction in alloy cost critical for acceptance in commercial applications

• Today’s Ga market price: $800 ‐$1000/ kg• Purchased at significant quantities (50

kg lots)• Prices trending up

• M.D. Brooks, E. Summers, R. Meloy, J. Mosley, “Aluminum additions in polycrystalline iron‐gallium (Galfenol) alloys,” Proc. SPIE 6929, 69291T (2008)• Focus on small diameter, 6.35mm,

FSZM samples• Fe80.6‐81.6Ga9.8‐13.8Al4.9‐9.8• Difficulty achieving consistent texture

• Scale‐up to Advance Bridgman stage, evaluate properties

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Galfenol Wire Fabrication

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• Part of a Phase II SBIR effort on energy harvesting

• Develop wire fabrication processing for Galfenol alloys• ETREMA/Ames Lab

• Several continuous feet of wire produced; 10 at% Ga

• Early on in process development

• Transition partner identified and interested in scaling‐up process if demand exists

Photos of the 0.014” diameter wire produced of the Fe90Ga10

After drawing

After HT

Galfenol (a non-REE smart technology)• Supply of Terbium and Dysprosium potentially a problem in the foreseeable future

• Gallium does not have the same supply risk

Figures copied from US Dept. of Energy, “Critical Materials Strategy – December 2010”, p. 8

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Galfenol Technology Roadmap6.3 (Technology Development)

6.2 (Advanced Research)

6.1 (Basic Research)

Galfenol Discovery

Processes Established

Actuators Energy Harvesters/Sensors

Properties Characterized

Multifunctional Structures

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Applications DevelopmentETREMA• Significant interest in using Galfenol for energy harvesting• Medical device tool in early development stage (actuator)• Very low frequency sources for US Navy

In all cases…costs to produce must be lowered• Reduce raw material costs• Scale‐up production

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Technology Commercialization• Current processing technologies nearing a cross‐road

• Alloying, Bridgman, Rolling, Stress Annealing, etc…• Only capable of producing small quantities

• Process scale‐up absolutely necessary to meet commercial application quantity and pricing requirements

• Scale‐up will require investment in equipment and infrastructure ($)• Difficult to obtain $$$ in today’s low‐risk economic environment

• End‐users must be open to negotiating and executing Supply Agreements

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