University of Wisconsin Applied Superconductivity Center Microstructure and Jc improvements in overpressure processed Ag-sheathed Bi-2223 tapes Yongwen Yuan, Jianyi Jiang, Xueyu Cai, Satyabrata Patnaik, Matt Feldmann, Anatoly Polyanskii, Eric Hellstrom and David Larbalestier University of Wisconsin–Madison Yibing Huang American Superconductor Corporation Bob Williams Oak Ridge National Laboratory Support from DOE-EERE and partial facilities support from NSF-MRSEC ASC 2002, Houston, TX
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University of Wisconsin Applied Superconductivity Center
Microstructure and Jc improvements in overpressure processed Ag-sheathed
Bi-2223 tapesYongwen Yuan, Jianyi Jiang, Xueyu Cai, Satyabrata Patnaik, Matt
Feldmann, Anatoly Polyanskii, Eric Hellstrom and David Larbalestier
University of Wisconsin–Madison
Yibing Huang
American Superconductor Corporation
Bob Williams
Oak Ridge National Laboratory
Support from DOE-EERE and partial facilities support from NSF-MRSEC
ASC 2002, Houston, TX
University of Wisconsin Applied Superconductivity Center
Overview
What is overpressure (OP) processing and why use it?OP improves microstructure OP increases JcSummary
University of Wisconsin Applied Superconductivity Center
Density varies through multi-step 2223 process
Density decreases as 2223 formsRolling increases densityCore can dedensify in final heat treatment10-30% porosity exists in best multifilament tapes
Cracks caused by IR never completely heal
tHT1 IR FHT
Rolli
ng
GT
4.4 5.6 4.65.6
Jiang et al. SuST 2001
Full density 6.3 g/cc
T
University of Wisconsin Applied Superconductivity Center
What is overpressure (OP) processing?
Applies isostatic pressure to compress samplesOP processing is a variant of hot isostatic pressing (HIP)Mixture of inert gas and O2
Inert gas applies pressure <200 atmpO2 sets thermodynamic condition needed to form 2223 pO2 = 0.075 atm
Ultimate Goal: 1 deformation/sinter (1DS) process
University of Wisconsin Applied Superconductivity Center
Overview of ORNL static OP system
Easy to change initial Ptotal and pO2, but gas is not replaced, Ptotal and pO2 change during run
Regulator
Shut Off Valve
Flow control valve
Reaction Chamber
Thermocouples
O2 and Ar Tanks
Pressure Gauge
Sample FurnaceClosure
University of Wisconsin Applied Superconductivity Center
Overview of UW flow OP system
Gas continuously replaced during run; Ptotal and pO2 remain constant
Relief ValveRegulators
Shut Off Valve
Flow Meter
High Pressure Mixed Ar/O2 Tank (400 bar) 500 ppm O2
Regulator
Shut Off Valve
Flow control valve
Reaction Chamber
Thermocouples
Pressure Gauge
Sample FurnaceClosure
University of Wisconsin Applied Superconductivity Center
UW flow OP system, 900°C, 200 atm1.3 m
University of Wisconsin Applied Superconductivity Center
Where to begin with OP?
Tmax, Ptotal, and pO2 are the most important OP parameters
• Use simple HT schedule to optimize Tmax
• Modify J.Jiang’s 1 atm processing schedule for OP
• Address pO2 uncertainty in OP gas mixture pO2 = 0.075 to 0.10 atm at 148 atm
University of Wisconsin Applied Superconductivity Center
Simple heat treatment to optimize Tmax
Ptotal=148atm, pO2=0.077atm (design)
Tmax
University of Wisconsin Applied Superconductivity Center
Microstructure as a function of Tmax, 148atm804C
812C
808C
816C 820C
812C
824C
University of Wisconsin Applied Superconductivity Center
Ic varies with temperature – OP 148 atm
804 808 812 816 820 824
25
30
35
40Ic
(A)
T ( 0C)
Green tape
University of Wisconsin Applied Superconductivity Center
OP thermal process
Begin with 1 atm HT developed by Jiang et al.
Ptotal=148 atm, pO2=0.077 atm (design)
Tmax
Simplified the 1 atm HT for OP processing
See Jiang – 2MM04 Tuesday 4:00pm
University of Wisconsin Applied Superconductivity Center
At Ptotal = 1 atm, pO2 has small influence on HT1 and IR, some on GT,
0.075 0.080 0.085 0.090 0.095 0.100 0.10510
20
30
40
50
60
GT
HT1
IR
Ic (A
)
pO2 (atm)
University of Wisconsin Applied Superconductivity Center
University of Wisconsin Applied Superconductivity Center
Direct comparison of connectivity
0
� XkA/cm2
OP1 atmX = 50 kA/cm2
Transport Jc: 1 atm 39 kA/cm2, OP 48 kA/cm2
University of Wisconsin Applied Superconductivity Center
What next?
Optimize OP processingCombine OP with other novel processesOP processing at low pressure
University of Wisconsin Applied Superconductivity Center
Nonsuperconducting 2nd phases and microporosity still in OP tape
Jc = 58.7 kA/cm2 , 148 atm
Ag
Ag
Ag
University of Wisconsin Applied Superconductivity Center
How low can Ptotal go?
Ptotal (atm)0 20 40 60 80 100 120 140 160
Rel
ativ
e de
nsity
(%)
75
80
85
90
95
100
University of Wisconsin Applied Superconductivity Center
SummaryOP improves Bi2223 microstructure by densifying filaments – remove porosity, heal cracksOP increases Jc by several mechanisms
OP increase Jc by ~20-70% wrt 1 atm processing, new record value of 22.4 kA/cm2 at 77K,0.1TOP increases Jc by densifying core, reducing 2212, improving connectivity
OP needs to be optimized – eliminate 2nd
phases and microporosityOP densifies tape at 65 atm, lower pressure experiments are underway