Detailed studies of tensile and delamination properties of REBCO coated conductors

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Stanley Mitchell Jefferson
5 years ago
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superior performance. powerful technology.

conductors Yifei Zhang, Masayasu Kasahara, Aarthi Sundaram, Paul

on Mechanical and Electromagnetic Properties of Composite

1 superior performance. powerful technology. 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 8 th Workshop on Mechanical and Electromagnetic Properties of Composite Superconductors (MEM 2016) March 21 23, 2016 Tallahassee, FL, USA SuperPower Inc. is a subsidiary of Furukawa Electric Co. Ltd.

2 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 All Rights Reserved. Copyright SuperPower Inc

REBCO wire production at SuperPower REBCO wire produced by IBAD-MOCVD on Hastelloy substrate Wire Type (REBCO formulation) AP (Advanced Pinning): enhanced in-field performance with Zr dopping CF

3 REBCO wire production at SuperPower REBCO wire produced by IBAD-MOCVD on Hastelloy substrate 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 µm) Insulation Splicing I c (77K, s.f.)/12mm= a Piece length= m All Rights Reserved. Copyright SuperPower Inc

4 Continuous wire development 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.) All Rights Reserved. Copyright SuperPower Inc

5 Mechanical and electromechanical testing at SuperPower Axial tensile test at room temperature or at 77K (with I c ) Measurement of elastic modulus and yield stress Determination of critical stress and irreversible stress (strain) Torsion-tension test at 77K (with I c ) Measurement of critical tensile stress under twist Transverse (c-axis) compressive test at 77K (with I c ) Measurement of critical compressive stress Bending test at 77K (with I c ) 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 I c ) All Rights Reserved. Copyright SuperPower Inc

6 Mechanical and electromechanical testing at SuperPower Transverse compression Uniaxial tension Torsion + tension Transverse tension Bending Test Peel Test Pin-Pull Test All Rights Reserved. Copyright SuperPower Inc

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 All Rights Reserved. Copyright SuperPower Inc

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 Tape Type E (GPa) 0.2 (MPa) n Bare REBCO Tape SCSXX50-20Cu SCSXX50-40Cu SCSXX50-100Cu Free-standing Cu All Rights Reserved. Copyright SuperPower Inc

12 Effects of axial tensile stress (strain) on critical current I c (0) original critical current of as-received wire I c critical current measured while a wire is under a stress I c critical current measured after the stress is completely released All Rights Reserved. Copyright SuperPower Inc

13 Defining critical stress/strain and irreversible stress/strain c,0.95 and c,0.95 are stress and strain at which I c =0.95I c (0) irr,0.99 and irr,0.99 are stress and strain after which I c =0.99I c (0) c,0.95 irr,0.99 c,0.95 irr,0.99 All Rights Reserved. Copyright SuperPower Inc

Determination of irreversible stress, irr,0.99 I c (0)=428.

15 Critical current measurement of bare REBCO tapes To facilitate repeated Ic measurement on one bare REBCO tape Bridged sample used (bridge width about 2.7mm) E=0.1µV/cm set as Ic criterion (lower cut-off voltage) Ag REBCO LMO All Rights Reserved. Copyright SuperPower Inc

20 Effect of Cu stabilizer Cu stabilizer volume fraction, Cu =(Cu stabilizer thickness)/(total thickness) c,0.95 irr, E 0.45 c,0.95 irr, Y. Zhang, et al, IEEE-TASC, Vol.26, No.4, (2016) All Rights Reserved. Copyright SuperPower Inc

23 Tensile testing of bonded wires Bonded wire #B, 4mm wide, Cu =0.75, I c (77K,s.f.)=135A Two SCS wires bonded to one pure copper strip (different from A) All Rights Reserved. Copyright SuperPower Inc

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 All Rights Reserved. Copyright SuperPower Inc

99, using SEM-FIB and OMI Micro cracks seen on 1% strained tape, in REBCO, and in buffer

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 All Rights Reserved. Copyright SuperPower Inc

27 Delamination is still an issue to some of applications 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 All Rights Reserved. Copyright SuperPower Inc

28 Summary 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 ( 0.2 ), critical stress ( c,0.95 ), and irreversible stress ( irr,0.99 ) decrease with increasing Cu thickness ratio Cu. Critical strain ( c,0.95 ) and irreversible strain ( irr,0.99 ) were relatively independent of Cu. Microstructural analysis indicated micro cracks formation as the tensile stress reaches above irr,0.99. All Rights Reserved. Copyright SuperPower Inc