Detailed studies of tensile and delamination properties of ...• Axial tensile tests were performed...

superior performance. powerful technology.

SuperPower Inc. is a subsidiary of Furukawa Electric Co. Ltd.

Detailed studies of tensile and delamination properties of REBCO coated conductors Yifei Zhang, Masayasu Kasahara, Aarthi Sundaram, Paul Brownsey, Allan Knoll, Hiroshi Kuraseko, and Drew Hazelton ! 8th Workshop on Mechanical and Electromagnetic Properties of Composite Superconductors (MEM 2016) ! March 21 – 23, 2016 ! Tallahassee, FL, USA

MEM 2016 ¡ Tallahassee, FL, USA ¡ March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016

Outline •  REBCO wire production and continuous R&D at SuperPower •  Mechanical and electromechanical testing at SuperPower •  Tensile testing of free-standing Cu stabilizer and bare REBCO tape •  Tensile testing of Cu-stabilized REBCO wires •  Stress-strain relationships calculation and curve fitting •  Critical stress/strain and irreversible stress/strain •  Effect of Cu stabilizer •  Tensile testing of bonded wires •  Delamination strength testing methodology •  Summary

2


REBCO wire production at SuperPower REBCO wire produced by IBAD-MOCVD on Hastelloy substrate

3

•  Wire Type (REBCO formulation) –  AP (Advanced Pinning): enhanced in-field performance with Zr dopping –  CF (Cable Formulation): for lower-field LN2-temperature applications

•  Spec –  Width (2, 3, 4, 6,12mm) − Substrate thickness (30, 50,100µm) –  Ag thickness (1-5µm) − Cu stabilizer thickness (total 10-115µm) –  Insulation − Splicing –  Ic(77K, s.f.)/12mm=300-600A − Piece length=300-500m

MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016

Continuous wire development

4

•! Wires on thinner substrates –! Higher engineering current density and enhanced mechanical flexibility –! For fabrication of high current cables and high-field magnets

•! Advanced Pinning (AP) formula tailored for different operating conditions –! Intermediate-temperature (30-50K) and intermediate-field (2-4T) applications –! Low-temperature (4.2K) high-field (>10T) applications

•! Bonded wires –! Enhanced performance –! Specific functionality

•! Wire filamentization –! Reduction of AC loss –! Mitigation of screening effect

•! Alternative insulation –! Thinner and more uniform

Low-temperature high-field performance with higher Zr doping, lower Ic(77K, s.f.)

Low-temperature (4.2K) high-field (>10T) applications

MEM 2016 ¡ Tallahassee, FL, USA ¡ March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 5

Mechanical and electromechanical testing at SuperPower

•  Axial tensile test at room temperature or at 77K (with Ic) −  Measurement of elastic modulus and yield stress −  Determination of critical stress and irreversible stress (strain)

•  Torsion-tension test at 77K (with Ic) −  Measurement of critical tensile stress under twist

•  Transverse (c-axis) compressive test at 77K (with Ic) −  Measurement of critical compressive stress

•  Bending test at 77K (with Ic) −  Measurement of minimum bending diameter

•  Measurement of delamination strength – various testing methods −  Peel test: at room temperature −  Pin-pull (c-axis tensile) test: at room temperature −  Anvil (c-axis tensile) test: at room temperature or at 77K (with Ic)

MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 6

Mechanical and electromechanical testing at SuperPower

Uniaxial tension Torsion + tension

Transverse tension

Transverse compression

Pin-Pull Test Peel Test Bending Test


Tensile testing of free-standing Cu stabilizer •! Free-standing Cu stabilizer samples prepared from peeling SCS12050 wires


Tensile testing of Hastelloy substrates and bare REBCO tapes


Tensile testing of Cu-stabilized (SCS) wires


Calculation of stress-strain relationships of SCS wires •! Using stress-strain relationship data of bare REBCO tape and free-standing Cu •! Assuming two components with equal strain


Fitting of stress-strain curves •! Fitting with Ramberg-Osgood equation

!! "#$%&"#$##%&"#$"#'#$%&&"'(!&

where E - elastic modulus !0.2 - yield stress " - Ramberg-Osgood parameter

Stress-strain curve fitting parameters, 77K

!"#$%!&#$ '%()*"+ !,-.%(/*"+ 0

!"#$%&'!()%*"+$ ,-. ,//0 012(2330.4/.(5 ,0. 66- 7-2(2330.48.(5 ,/0 960 7-2(2330.4,..(5 6- 0-. 7-:#$$4;<"=>?=@%(5 -0 776 ,0


Effects of axial tensile stress (strain) on critical current •! Ic(0) – original critical current of as-received wire •! Ic – critical current measured while a wire is under a stress •! Ic# – critical current measured after the stress is completely released


Defining critical stress/strain and irreversible stress/strain •! !c,0.95 and $c,0.95 are stress and

strain at which Ic=0.95Ic(0)

!c,0.95

$c,0.95

!irr,0.99

•! !irr,0.99 and $irr,0.99 are stress and strain after which Ic#=0.99Ic(0)

Tallahassee, FL, USA March 21 – 23, 2016

$irr,0.99


Determination of irreversible stress, !irr,0.99

!irr,0.99

Ic(0)=428.8A


Critical current measurement of bare REBCO tapes

Ag REBCO LMO

•! To facilitate repeated Ic measurement on one bare REBCO tape ! Bridged sample used (bridge width about 2.7mm) ! E=0.1"V/cm set as Ic criterion (lower cut-off voltage)


Ic/Ic(0) vs. stress, and !c,0.95 (critical stress)

Bare REBCO tape 20"m Cu

40"m Cu

100"m Cu

77K, 50!m Hastelloy


Ic/Ic(0) vs. strain, and $c,0.95 (critical strain)

Bare REBCO tape

20!m Cu

40!m Cu

100!m Cu

77K, 50!m Hastelloy


Ic#/Ic(0) vs. stress, and !irr,0.99 (irreversible stress)

Bare REBCO Tape

20!m Cu

40!m Cu

100!m Cu


Ic#/Ic(0) vs. strain, and $irr,0.99 (irreversible strain)

20!m Cu

Bare REBCO Tape

40!m Cu

100!m Cu


Effect of Cu stabilizer Cu stabilizer volume fraction, %Cu=(Cu stabilizer thickness)/(Total thickness)

Y. Zhang, et al, IEEE-TASC, Vol.26, No.4, (2016)8400406

!c,0.95 !irr,0.99 !0.2 E0.45 $c,0.95 $irr,0.99 $0.2


!c,0.95 and !irr,0.99 on stress-strain curves

$irr,0.99

!irr,0.99

$c,0.95

!c,0.95


Tensile testing of bonded wires •! Bonded wire #A, 12mm wide, %Cu=0.41, Ic(77K,s.f.)=800A

! Two SCS wires bonded to one pure copper strip,


Tensile testing of bonded wires •! Bonded wire #B, 4mm wide, %Cu=0.75, Ic(77K,s.f.)=135A

! Two SCS wires bonded to one pure copper strip (different from A)


Tensile testing of bonded wires •! Bonded wire #C, 3mm wide, %Cu=0.87, Ic(77K,s.f.)=111A

! One SCS wires bonded to one copper alloy strip,


Microstructural analysis of tensile tested wires

•! Irreversible microstructural changes occur at $>$irr,0.99 •! Comparative analysis of microstructure for $ below and above $irr,0.99, using

OMI and SEM-FIB

1%, ZFC T=20K H=61.6mT A. Polyanskii, D. Abraimov, ASC/NHMFL


Microstructural analysis of tensile tested wires

•! Comparative analysis of microstructure for $ below and above $irr,0.99, using SEM-FIB and OMI

•! Micro cracks seen on 1% strained tape, in REBCO, and in buffer

1% strained, SEM, REBCO surface 1% strained, SEM, LMO surface

A. Polyanskii, D. Abraimov, ASC/NHMFL

MEM 2016 ¡ Tallahassee, FL, USA ¡ March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 27

Delamination is still an unresolved issue

•  What is the exact mechanism? •  What are the controlling structural characteristics? •  What are the dominant processing parameters? •  What are the best testing methods?

Method RT LN2 Quantitative QC Tool Before Ag/Cu

Pin-Pull Test Y N Y N N

Anvil Test Y Y Y N N

Peel Test Y N Y Y N

?? Y N N Y Y

?? Y N Y Y Y


Summary

28

•  Axial tensile tests were performed on free standing Cu stabilizer and bare REBCO tapes, providing fundamental and important tensile property data.

•  Stress-strain relationship of a Cu stabilized wire can be estimated with calculation using a two-component composite equal-strain model.

•  Measured stress-strain curves can be well fitted with the Ramberg-Osgood equation.

•  Elastic modulus (E), yield stress (σ0.2), critical stress (σc,0.95), and irreversible stress (σirr,0.99) decrease with increasing Cu thickness ratio γCu.

•  Critical strain (εc,0.95) and irreversible strain (εirr,0.99) were relatively independent of γCu.

•  Microstructural analysis indicated micro cracks formation as the tensile stress reaches above σirr,0.99.

Detailed studies of tensile and delamination properties of ...• Axial tensile tests were performed...

Documents

Transcript of Detailed studies of tensile and delamination properties of ...• Axial tensile tests were performed...