[M-02:RE123 conductors processing and properties]
Andong National University
ICEC25/ICMC 2014, at the University of Twente
Reversible Ic Degradation Behaviour in REBCO Coated Conductor Tapes under Transverse Stress*
Hyung-Seop
y g
p Shin1, Alkingg Gorospe
p 1,2 and Arman Rayy Nisayy1
1Department
of Mechanical Design Engineering, Andong National University, Korea, & 2Department of Engineering, Aurora State College of Technology, Philippines
Results and Discussion
0.9
0.8
0.7
2: 225 A
Loading
Unloading
3: 216 A
Loading
Unloading
5
10
10
15
15
20
20
25
30
35
25
40
30
45
35
40
45
50
0.6
0.99
0.97
0.96
0.3
0.95
0.94
0 93
0.93
0.92
0.2
0.1
Test 4: 213 A
0
0.90
5
5
10
10
15
20
20
25
30
35
40
45
50
Mechanicaldelamination
Mechanical
delamination strength&morphologies
55
50
45
45
40
40
n-values
s
es
n-value
Mechanical delamination strength of CC tapes
35
30
25
20
30
25
20
15
Test 1
Test 2
Test 3
10
5
0
Test 4
0
0
5
10
15
20
25
30
35
40
45
50
0
5
10
15
20
25
30
35
40
45
50
Transverse tensile strength, MPa
Transverse tensile strength, MPa
Current
terminal
15
25
30
35
40
45
50
Transverse
tensile
stress,
MPa
 Morphologies of delaminated CC tape under electromechanical delamination testing showed
good correlation with the Ic degradation behavior.
 Test 4 was delaminated mostly within the GdBCO superconducting layer where in this case the
Ic degraded in a gradual manner presenting a high electromechanical delamination strength.
Transverse tensile stress, MPa
 CC tapes with stainless steel substrate exhibited both abrupt & gradual Ic degradation behaviors.
i i
i
i i strength off 26.5
26 MPa,
 Test 11, Test 22, Test 3 and Test 4 exhibited
electromechanical
delamination
35 MPa , 32 MPa and 43 MPa, respectively with an average value of 34.1 MPa.
 Tests 1 (abrupt Ic degradation), 2 & 3 (gradual Ic degradation) showed reversible Ic (= or above
99% Ic retention) when unloaded to 20 N until the delamination occurred.
 Test 4 (gradual Ic degradation), however, there existed a reversible stress limit Ic (below 99 % Ic
retention) of 32.5 MPa when unloaded to 20 N before complete delamination occurred.
 The n value-transverse stress relation showed a good correlation with the Ic behavior under
transverse tensile stress for each test.
Morphologies of delaminated CC tapes
50
High
40
30
Medium
20
Delamination sites:
10
w/ in REBCO layer
Low
0
1
2
3
4
5
6
7
8
9
10
REBCO/buffer layer
Buffer/substrate layer
Substrate/copper layer
Test number
H.S. Shin et. al, Supercond. Sci. Tech., 27 (2014) 025001
 Exhibited wide scattering of mechanical delamination strength over the three levels classified
(9 MPa ~ 49 MPa).
 The Cu-stabilized GdBCO CC tapes with stainless steel substrate had almost similar values in
both mechanical and electromechanical delamination strength.
 CC tapes with low and medium mechanical delamination strength were mostly delaminated
between the GdBCO/Ag interface, while high ones mostly delaminated between substrate/
buffer, buffer/GdBCO interfaces and within the GdBCO superconducting film itself.
 Comparison of Ic degradation behavior under uniaxial loading
Stress based
0.8
 5 kN loadcell capacity
 10 min pre-cooling before submerge to
liquid nitrogen at 77 K
K.
 Crosshead velocity = 0.1 mm/min (mechanical)
 Load controlled - 30 N interval
(electromechanical)
 Soldering was done using the 4 x 8 mm upper anvil at 120oC~ 130oC with an In-Bi solder
(melting point of 70.9 oC).
 Voltage tap separation of 2 cm and voltage tap criterion for Ic measurement of 1 μV/cm was
adopted.
Norma
alized critical current, Ic/Ic0
1.01
Voltage taps
1.00
0.6
0.99
0.98
0.97
irr = 654 MPa
0.4
0.96
0.95
0.94
0.2
0.93
0.92
0.91
Loading
Unloading
0.0
0.90
0
Conclusions
1.0
No
ormalized critical current, Ic/Ic0
No
ormalized critical current, Ic/Ic0
1.0
Substrate side
Reversibility limit
Loading
Unloading
0.0
0.91
Substrate/buffer layer
0.4
50
5
GFRP insulation
Superconductor
side
Area in contact (32 mm2)
0.5
0.98
55
10
Setupformechanicalandelectromechanical
Setupformechanicalandelectromechanicaldelamination
delamination test
Loading
direction
Test 3
0.7
1.00
0
50
strength, MPa
Edge cracks
0.8
15
 Jig for good alignment
Wire rope
(single point contact)
1: 220 A
Loading
Transverse
tensile
Transverse
tensile strength,
MPa
GdBCO superconducting film
0.9
 N-values
SpecificationsandpropertiesofGdBCOCCtapesample
Conducting film
Substrate
Ic , A
Dimension, t x w
Stabilizer
Manufacturer
1.01
Normalized critical current, Ic/Ic0
1.02
1.01
0.6
1.00
0.99
0.98 0.5
0.97
0.96 0.4Test
0.95
0.94
0.3
0.93
Test
0.92
0.91 0.2
0.90
0.89 0.1
Test
0.88
0.87
0.0
0.86
0
0.85
0
5
Normalized critical current, Ic/Ic0
N
1.0
1.0
35
Reactive Co-evaporation by
Deposition and Reaction (RCE-DR)
GdBCO(1-2 m)
Stainless steel (~104 m)
> 220
0.135 x 4.06 (slit)
Electroplated Copper (15 m)
SuNAM
T t2
Test
1.1
Sample and methodology
Fabrication process
Test 4
 Irreversible Ic before complete delamination
Mechanical delamination streng
gth, MPa
To investigate the mechanical and electromechanical properties of GdBCO CC tape adopting
stainless steel (STS) substrate under transverse load using anvil test.
To examine the reversible Ic degradation behaviors under transverse stress.
To investigate delamination mechanism of the CC tape under transverse loading.
 Reversible Ic until delamination
No
ormalized criticla current, Ic/Ic0
Obj ti
Objectives
MorphologiesofCCtape
Test 1
Criticalcurrent,IIc degradationbehavior
Criticalcurrent,
Normaliz
zed criticla current, Ic/Ic0
Introduction
2G REBCO coated conductor (CC) tapes gained its popularity in electric applications such as
motor and generators, power cables, and especially coils due to its superior characteristics and
performance.
In coil applications, the CC tapes might experience several factors that might limit its
performance possibly damage its integrity through the delamination of its layers.
Large Lorentz force, CTE mismatch of constituent layers, screening current and other fabrication
related reasons produce excessive transverse stresses.
As reported elsewhere, the critical current, Ic of impregnated coil was completely degraded due to
the delamination of the CC tape’s layer.
Therefore, in coil design, mechanical and electromechanical delamination strength of the CC tape
should be enough to withstand these threatening factors for the optimum design.
0
100
200
Loading
Unloading
100300
200
400
300 600
500
400
700
Uniaxial tensile
stress, MPa
Uniaxial
tensile
500
800
600
stress, MPa
700
800
irr = 0.80 %
0.9
0.8
0.7
0.6
0.5
 Strain based
0.4
0.3
0.2
Loading
Unloading
0.1
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Uniaxial strain, %
 When compared, the behavior under transverse stress with the one under uniaxial loading,
the GdBCO CC tapes with STS substrate exhibited similar Ic degradation behavior.
Under uniaxial tensile loading, the Cu-stabilized CC tape with stainless steel substrate
exhibited a reversible Ic stress limit (stress where Ic is above 99% Ic0) at 654 MPa.
1.0
1.1
RCE-DR processed GdBCO CC tape with stainless steel substrate exhibited both abrupt and
gradual Ic degradation behavior under transverse loading.
Under transverse tensile, Ic of CC tape showed reversible degradation behavior similar with
the one under uniaxial tensile loading.
RCE-DR GdBCO CC tapes with stainless steel substrate showed almost similar mechanical and
electromechanical delamination strength, which are different from the Hastelloy substrate case.
Exhibited multiple delamination sites and resulted to variation in mechanical delamination
strength obtained, CC tape with low mechanical delamination strength mostly delaminates
between the GdBCO/Ag interface while CC tape with high mechanical delamination strength
mostly exhibits delamination between substrate/buffer, buffer/GdBCO interfaces and within
the GdBCO coating film itself.
*This work was supported by a grant from National Research Foundation of Korea (NRF-2014-002640) & BK21 PLUS program funded by the Ministry of Education, Science
& Technology (MEST), Republic of Korea. This work was also partially supported by a grant from the Power Generation & Electricity Delivery Program of the Korea Institute
of Energy Technology Evaluation and Planning (KETEP) funded by the Ministry of Trade, Industry and Energy.