Upload
others
View
5
Download
0
Embed Size (px)
Citation preview
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
MEM 2016 ¡ Tallahassee, FL, USA ¡ March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016
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
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 7
Tensile testing of free-standing Cu stabilizer •! Free-standing Cu stabilizer samples prepared from peeling SCS12050 wires
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 8
Tensile testing of Hastelloy substrates and bare REBCO tapes
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 9
Tensile testing of Cu-stabilized (SCS) wires
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 10
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
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 11
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
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 12
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
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 13
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
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 14
Determination of irreversible stress, !irr,0.99
!irr,0.99
Ic(0)=428.8A
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 15
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)
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 16
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
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 17
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
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 18
Ic#/Ic(0) vs. stress, and !irr,0.99 (irreversible stress)
Bare REBCO Tape
20!m Cu
40!m Cu
100!m Cu
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 19
Ic#/Ic(0) vs. strain, and $irr,0.99 (irreversible strain)
20!m Cu
Bare REBCO Tape
40!m Cu
100!m Cu
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 20
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
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 21
!c,0.95 and !irr,0.99 on stress-strain curves
$irr,0.99
!irr,0.99
$c,0.95
!c,0.95
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 22
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,
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 23
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)
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 24
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,
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 25
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
MEM 2016 ! Tallahassee, FL, USA ! March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016 26
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
MEM 2016 ¡ Tallahassee, FL, USA ¡ March 21 – 23, 2016 All Rights Reserved. Copyright SuperPower® Inc. 2016
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.