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Najib Cheggour - One of the best experts on this subject based on the ideXlab platform.
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precipitous change of the irreversible Strain Limit with heat treatment temperature in nb 3 sn wires made by the restacked rod process
Scientific Reports, 2018Co-Authors: Najib Cheggour, Loren F Goodrich, Jolene D Splett, Theodore C Stauffer, William L Starch, P J Lee, A GhoshAbstract:The intrinsic irreversible Strain Limit eirr,0 of Nb3Sn superconducting wires, made by the restacked-rod process and doped with either Ti or Ta, undergoes a precipitous change as a function of temperature θ of the final heat-treatment for forming the A15 phase. Nb3Sn transitions from a highly brittle state where it cracks as soon as it is subjected to an axial tensile Strain of any measurable amount, to a state more resilient to tensile Strain as high as 0.4%. The remarkable abruptness of this transition (as most of it occurs over a range of only 10 °C) could pose real challenges for the heat-treatment of large magnets, such as those fabricated for the high-luminosity upgrade of the Large Hadron Collider (LHC). We named this behavior the Strain irreversibility cliff (SIC) to caution magnet developers. The approach to fulfilling application requirements just in terms of the conductor’s residual resistivity ratio RRR and critical-current density Jc is incomplete. Along with RRR and Jc wire specifications, and sub-element size requirements that reduce wire magnetization and instabilities effects, SIC imposes additional conStraints on the choice of heat-treatment conditions to ensure mechanical integrity of the conductor.
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influence of the heat treatment conditions microchemistry and microstructure on the irreversible Strain Limit of a selection of ti doped internal tin nb3sn iter wires
Superconductor Science and Technology, 2014Co-Authors: Najib Cheggour, Loren F Goodrich, Jolene D Splett, Theodore C Stauffer, P J Lee, Zu Hawn Sung, M C JewellAbstract:Systematic studies of the intrinsic irreversible Strain Limit eirr,0, microstructure, and microchemistry were made on several internal-tin Nb3Sn pre-production wires, fabricated for the domestic agencies of the USA and China participating in the International Thermonuclear Experimental Reactor. These wires were produced by Luvata, Oxford Superconducting Technology (OST), and Western Superconducting Technologies (WST), and were intended for the tokamak's toroidal-field coils. The results of this study show that, for a final heat-treatment at 650 °C to form the A15 phase, both eirr,0 and the de-pinning field Bc2* improved by increasing heat-treatment duration beyond 100 h for the Luvata wires. On the other hand, we saw no improvement in these two parameters as a function of heat-treatment duration in the OST wires. Furthermore, micro-chemical analysis of OST wires revealed that some Nb3Sn filaments have a Sn- and Ti-rich phase at the interface between Cu(Sn) matrix and Nb3Sn in the form of a shell around individual filaments. This phase is far less prominent in the Luvata and WST conductors, and could inhibit diffusion of Sn and Ti into Nb3Sn filaments during the reaction and may potentially be the reason for the lack of noticeable change in Bc2* with heat-treatment duration in the OST wires. The increase of eirr,0 and Bc2* with heat-treatment duration in the Luvata wires and the lack of increase in the OST wires may suggest a possible correlation between eirr,0 and the stoichiometry of the A15 composition. Investigation of the samples' microstructure revealed only a small number of cracked Nb3Sn filaments despite the significant and permanent degradation of their critical current Ic when subjected to longitudinal tensile Strain e beyond eirr,0. The scarcity of cracks indicate that Ic(e) measurements are highly sensitive to crack formation in Nb3Sn filaments, especially at low electric-field criteria 0.1 μV cm−1, even when the sizes of the individual filaments are only few micrometers. All the strands contained substantial Kirkendall porosity, but we found that the quantity and distribution of the Kirkendall voids vary significantly with strand design. Luvata wires have the least porosity, followed by WST wires, and then by OST strands. However, even though the presence of cracks in the Nb3Sn filaments that are in close proximity to Kirkendall voids suggest a correlation between crack initiation and the proximity of the filaments to these voids, the porosity investigation established no definitive relationship between porosity and eirr,0 in the wires studied.
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enhancement of the irreversible axial Strain Limit of y ba cu o coated conductors with the addition of a cu layer
Applied Physics Letters, 2005Co-Authors: Najib Cheggour, John W. Ekin, Y Y. Xie, Venkat Selvamanickam, C L H Thieme, D T VerebelyiAbstract:A Cu protection layer added to yttrium-barium-copper-oxide-(YBCO-) coated conductors substantially enhances the irreversible Strain Limit ϵirr for the onset of permanent electrical damage of the composite. This enhancement is of significance since it enables these conductors to meet the most severe Strain requirements for applications such as electric generators. The conductors studied had either a Hastalloy-C substrate with an ion-beam-assisted deposition template or a rolling-assisted biaxially textured Ni-W substrate. The irreversible Strain Limit, obtained from critical-current measurements as a function of axial tensile Strain at 76 K and self-field, increased from about 0.4% to more than 0.5% for both types of coated conductors with an added Cu layer, either by electroplating or lamination. This improvement is due only partially to the differential thermal contraction between Cu and the other conductor components. We believe that the Cu layer also enhances the fracture toughness of YBCO, thus acting...
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Reversible axial-Strain effect in Y-Ba-Cu-O coated conductors*
Superconductor Science and Technology, 2005Co-Authors: Najib Cheggour, John W. Ekin, Cornelis Leo Hans Thieme, Y Y. Xie, Venkat Selvamanickam, Ron FeenstraAbstract:The recently discovered reversible Strain effect in Y?Ba?Cu?O (YBCO) coated conductors contrasts with the general understanding that the effect of Strain on the critical-current density Jc in practical high-temperature superconductors is determined only by crack formation in the ceramic component. Instead of having a constant Jc as a function of Strain before an irreversible drop when cracks form in the superconductor, Jc in YBCO coated conductors can decrease or increase reversibly with Strain over a significant Strain range up to an irreversible Strain Limit. This reversible effect is present in samples fabricated either with rolling-assisted biaxially textured Ni?W substrates or with ion-beam-assisted deposition on Hastalloy substrates. The reversibility of Jc with Strain is observed for thin as well as thick YBCO films, and at two very different temperatures (76 and 4?K). The reversible effect is dependent on temperature and magnetic field, thus indicating its intrinsic nature. We also report an enhancement of the irreversible Strain Limit ?irr where the reversible Strain effect ends and YBCO cracking starts. The value of ?irr increases from about 0.4% to more than 0.5% when YBCO coated conductors are fabricated with an additional Cu protection layer.
Marlon J Dedicatoria - One of the best experts on this subject based on the ideXlab platform.
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reversible Strain response of critical current in differently processed gdbco coated conductor tapes under magnetic fields
IEEE Transactions on Applied Superconductivity, 2013Co-Authors: Hyung-seop Shin, Alking Gorospe, Hidetoshi Oguro, Marlon J Dedicatoria, T Suwa, Satoshi AwajiAbstract:In this study, the reversible response of Ic with uniaxial Strain in differently processed GdBCO coated conductor tapes with different substrates has been investigated under self field and magnetic field conditions at 77 K. Higher irreversible Strain Limit, eirr was observed in those samples with stainless steel substrate. Additional brass lamination to the Cu-stabilized samples produced enhancement of both eirr and endurable load Limit. However, no significant widening of the Ic/Ic0-tensile Strain window with brass addition was observed in the case of samples having stainless steel substrate. Furthermore, under magnetic field, the Ic degradation behavior was independent on the kind of substrate material, but varied with the kind of manufacturing process adopted. The GdBCO samples showed different Ic peak positions and degradation behavior depending on the level of magnetic field applied.
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intrinsic Strain effect on critical current in cu stabilized gdbco coated conductor tapes with different substrates
Superconductor Science and Technology, 2013Co-Authors: Hyung-seop Shin, Marlon J DedicatoriaAbstract:The intrinsic Strain effect on critical current, Ic in Cu-stabilized GdBCO coated conductor (CC) tapes under bending and uniaxial tension has been investigated. The bending deformation tolerance of Ic in GdBCO CC tapes, fabricated by reactive co-evaporation by deposition and reaction (RCE-DR) with substrate materials of Hastelloy and stainless steel and fabricated by the metal organic chemical vapour deposition (MOCVD) process was evaluated. The intrinsic Strain response of Ic under bending was found to be independent of the fabrication process, the substrate material and the geometry of the sample. For samples with a Hastelloy substrate, the intrinsic Strain response of Ic/Icmax under bending was well correlated with those under uniaxial tension. However, for samples with a stainless steel substrate, these had a large Strain sensitivity for Ic under uniaxial tension even though this showed a much higher irreversible Strain Limit up to 1.05%.
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determination of winding diameter based on bending Strain analysis for rebco coated conductor tapes
Progress in Superconductivity and Cryogenics, 2012Co-Authors: M De Leon, Marlon J Dedicatoria, Hyung-seop ShinAbstract:In order to recognize the allowable bending diameter in coils, the Strain as function of diameters is evaluated. The irreversible Strain Limits of in the easy and hard bending modes were measured. Strains were calculated at the coating film in the easy bending and at outer edge or inner edge in the hard bending of the CC tape, respectively. The tape geometry subjected to bending procedures is considered from the current industrial spool winding operation. Through the linear superposition of Strain induced in different bending modes regarding the expressions, the appropriate design for critical bending diameter is suggested. Results proved that the existence of buckling resulting from bending in hard direction when applied Strain exceeded 0.6% is possible. The depicted results showed that the Strain Limit as a viable parameter should be considered for future purposes.
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characteristic Strain response of rm i _ rm c in smbco coated conductor tapes under magnetic field at 77 k
IEEE Transactions on Applied Superconductivity, 2012Co-Authors: Hyung-seop Shin, Satoshi Awaji, Marlon J Dedicatoria, K WatanabeAbstract:SmBCO and YBCO coated conductors (CC) showed different critical current, Ic degradation behavior with Strain showing different Ic peak position under self field. Strain effect on Ic under magnetic field in REBCO CC tapes was investigated in order to measure and to describe its tolerance and degradation behavior. Katagiri-type tensile testing apparatus was adopted in which magnetic field was applied parallel to the c-axis of coating film using 10 T superconducting magnet at 77 K. Both Strain gauge and Nyilas double extensometers were used to measure the Strain. In all the REBCO CC tapes investigated, Ic(e, B) strongly depends on magnetic field and their degradation behavior depends on the kind of HTS film and fabrication technique adopted. Differently with YBCO CC tapes, SmBCO CC tapes showed increasing Ic Strain sensitivity with increasing magnetic field at 77 K and the irreversible Strain Limit was magnetic field independent over the entire field range studied.
Hyung-seop Shin - One of the best experts on this subject based on the ideXlab platform.
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characteristic irreversible critical Strain Limit of gdbco coated conductor tapes under various temperature and magnetic field conditions
IEEE Transactions on Applied Superconductivity, 2016Co-Authors: Alking Gorospe, Hyung-seop Shin, Zhierwinjay Bautista, Hidetoshi Oguro, Satoshi AwajiAbstract:Superior mechanical and electromechanical properties of the coated conductor (CC) tapes made them a viable option for coil and magnet applications. In this study, investigation on the characteristics of I c under different B, T, and e conditions were conducted. Tensile load was applied using the Katagiri type test rig under different high magnetic field and low-temperature conditions wherein irreversible Strain, e irr was determined. The I c behavior with magnetic field of both reactive co-evaporation by deposition and reaction (RCE-DR) and metal organic chemical vapor deposition (MOCVD) processed CC tapes at different T and B were obtained. The critical irreversible Strain Limit e irr of Cu-stabilized REBCO CC tape increased with decreasing temperature from 65 K down to 20 K. This behavior was resulted from the increased yield strength of the CC tape due to thermal hardening effect.
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reversible Strain response of critical current in differently processed gdbco coated conductor tapes under magnetic fields
IEEE Transactions on Applied Superconductivity, 2013Co-Authors: Hyung-seop Shin, Alking Gorospe, Hidetoshi Oguro, Marlon J Dedicatoria, T Suwa, Satoshi AwajiAbstract:In this study, the reversible response of Ic with uniaxial Strain in differently processed GdBCO coated conductor tapes with different substrates has been investigated under self field and magnetic field conditions at 77 K. Higher irreversible Strain Limit, eirr was observed in those samples with stainless steel substrate. Additional brass lamination to the Cu-stabilized samples produced enhancement of both eirr and endurable load Limit. However, no significant widening of the Ic/Ic0-tensile Strain window with brass addition was observed in the case of samples having stainless steel substrate. Furthermore, under magnetic field, the Ic degradation behavior was independent on the kind of substrate material, but varied with the kind of manufacturing process adopted. The GdBCO samples showed different Ic peak positions and degradation behavior depending on the level of magnetic field applied.
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intrinsic Strain effect on critical current in cu stabilized gdbco coated conductor tapes with different substrates
Superconductor Science and Technology, 2013Co-Authors: Hyung-seop Shin, Marlon J DedicatoriaAbstract:The intrinsic Strain effect on critical current, Ic in Cu-stabilized GdBCO coated conductor (CC) tapes under bending and uniaxial tension has been investigated. The bending deformation tolerance of Ic in GdBCO CC tapes, fabricated by reactive co-evaporation by deposition and reaction (RCE-DR) with substrate materials of Hastelloy and stainless steel and fabricated by the metal organic chemical vapour deposition (MOCVD) process was evaluated. The intrinsic Strain response of Ic under bending was found to be independent of the fabrication process, the substrate material and the geometry of the sample. For samples with a Hastelloy substrate, the intrinsic Strain response of Ic/Icmax under bending was well correlated with those under uniaxial tension. However, for samples with a stainless steel substrate, these had a large Strain sensitivity for Ic under uniaxial tension even though this showed a much higher irreversible Strain Limit up to 1.05%.
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determination of winding diameter based on bending Strain analysis for rebco coated conductor tapes
Progress in Superconductivity and Cryogenics, 2012Co-Authors: M De Leon, Marlon J Dedicatoria, Hyung-seop ShinAbstract:In order to recognize the allowable bending diameter in coils, the Strain as function of diameters is evaluated. The irreversible Strain Limits of in the easy and hard bending modes were measured. Strains were calculated at the coating film in the easy bending and at outer edge or inner edge in the hard bending of the CC tape, respectively. The tape geometry subjected to bending procedures is considered from the current industrial spool winding operation. Through the linear superposition of Strain induced in different bending modes regarding the expressions, the appropriate design for critical bending diameter is suggested. Results proved that the existence of buckling resulting from bending in hard direction when applied Strain exceeded 0.6% is possible. The depicted results showed that the Strain Limit as a viable parameter should be considered for future purposes.
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characteristic Strain response of rm i _ rm c in smbco coated conductor tapes under magnetic field at 77 k
IEEE Transactions on Applied Superconductivity, 2012Co-Authors: Hyung-seop Shin, Satoshi Awaji, Marlon J Dedicatoria, K WatanabeAbstract:SmBCO and YBCO coated conductors (CC) showed different critical current, Ic degradation behavior with Strain showing different Ic peak position under self field. Strain effect on Ic under magnetic field in REBCO CC tapes was investigated in order to measure and to describe its tolerance and degradation behavior. Katagiri-type tensile testing apparatus was adopted in which magnetic field was applied parallel to the c-axis of coating film using 10 T superconducting magnet at 77 K. Both Strain gauge and Nyilas double extensometers were used to measure the Strain. In all the REBCO CC tapes investigated, Ic(e, B) strongly depends on magnetic field and their degradation behavior depends on the kind of HTS film and fabrication technique adopted. Differently with YBCO CC tapes, SmBCO CC tapes showed increasing Ic Strain sensitivity with increasing magnetic field at 77 K and the irreversible Strain Limit was magnetic field independent over the entire field range studied.
M Sugano - One of the best experts on this subject based on the ideXlab platform.
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Strain induced irreversible critical current degradation in highly dense bi 2212 round wire
Superconductor Science and Technology, 2015Co-Authors: R Bjoerstad, J Jiang, M Sugano, C Scheuerlein, M O Rikel, A Ballarino, L Bottura, M Matras, J Hudspeth, M Di MichielAbstract:The Strain induced critical current degradation of overpressure processed straight Bi-2212/Ag wires has been studied at 77 K in self-field. For the first time superconducting properties, lattice distortions, composite wire stress and Strain have been measured simultaneously in a high energy synchrotron beamline. A permanent Ic degradation of 5% occurs when the wire Strain exceeds 0.60%. At a wire Strain of about 0.65% a drastic n-value and Ic reduction occur, and the composite stress and the Bi-2212 lattice parameter reach a plateau, indicating Bi-2212 filament fracturing. The x-ray diffraction measurements show that Bi-2212 exhibits linear elastic behaviour up to the irreversible Strain Limit.
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reversible Strain Limit of critical currents and universality of intrinsic Strain effect for rebco coated conductors
Superconductor Science and Technology, 2009Co-Authors: Kozo Osamura, M Sugano, Kohichi Nakao, Yuh Shiohara, A Ibi, Yutaka Yamada, Naoji Nakashima, Shigeo Nagaya, Takashi Saitoh, Yasuhiro IijimaAbstract:Intensive research work has been carried out in order to develop industrially available HTS REBCO-coated conductors under the NEDO project in Japan. Recently, several groups in the project succeeded in the development of high performance coated conductors. Their characteristic features have been evaluated in terms of mechanical properties and their influence on critical currents. The mechanical properties at RT and 77 K were analyzed on the basis of the rule of mixtures. The force-free Strain (Aff) was analytically deduced, which indicates the Strain at which the residual stress exerted on the superconducting layer becomes zero. Tensile Strain dependence on critical currents could be divided into elastic and brittle regions. The reversible Strain Limit (Arev) was defined as a Strain at which the critical current recovers elastically to the level of 99% Ico. Within the elastic region, the critical current showed a convex Strain dependence, which is explained as Ekin's intrinsic Strain effect. The degradation beyond the reversible Strain Limit was attributed to a fracture of the superconducting layer. As a whole, the present study made clear quantitatively the tensile Strain behavior of critical currents and proposed a reasonable definition for the reversible Strain Limit.
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intrinsic Strain effect on critical current and its reversibility for ybco coated conductors with different buffer layers
Superconductor Science and Technology, 2005Co-Authors: M Sugano, Kozo Osamura, W Prusseit, R Semerad, K Itoh, T KiyoshiAbstract:The uniaxial Strain dependence of the critical current was examined for YBCO coated conductors with IBAD-CeO2/YSZ or ISD-MgO buffer layers on Hastelloy substrates. Ic increased with increasing applied Strain, reached a maximum and decreased for higher Strain values. The reversible Strain region of Ic variation was observed. The reversible Strain Limit depends on the buffer layers. For the CeO2/YSZ buffered tape, Ic recovered the initial value even after the applied Strain reached 0.30%. On the other hand, an irreversible degradation of Ic was observed at the Strain less than 0.22% for the MgO buffered tape. The overall relationship between the Ic normalized by the peak value and the intrinsic Strain in YBCO obeyed a unified scaling function. Quenching occurred at the Strain close to the yield Strain of the Hastelloy substrate.
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Reversible Strain dependence of critical current in 100 a class coated conductors
IEEE Transactions on Applied Superconductivity, 2005Co-Authors: M Sugano, Kozo Osamura, W Prusseit, R Semerad, K Itoh, T. Kuroda, T KiyoshiAbstract:The Strain dependence of the critical current was studied for YBCO and DyBCO coated conductors with different buffer layers on Hastelloy substrates. A maximum of I/sub c/ was observed for both the YBCO and DyBCO tapes, however the sign of the Strain at the I/sub c/ peak was opposite for the two superconductors. A reversible variation of I/sub c/ with applied Strain was found and the reversible Strain Limit was observed to depend on the buffer layer. For the IBAD-CeO/sub 2//YSZ buffered YBCO tapes, I/sub c/ recovers reversibly when the applied Strain is reduced starting from 0.30%. For those with an ISD-MgO buffer layer the irreversible degradation starts at a Strain less than 0.22%. The reason for this difference is discussed based on microscopic observations. Quenching occurred during V-I measurements after the applied Strain exceeded 0.30%, which is close to the yield Strain of the composite tape.
Loren F Goodrich - One of the best experts on this subject based on the ideXlab platform.
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precipitous change of the irreversible Strain Limit with heat treatment temperature in nb 3 sn wires made by the restacked rod process
Scientific Reports, 2018Co-Authors: Najib Cheggour, Loren F Goodrich, Jolene D Splett, Theodore C Stauffer, William L Starch, P J Lee, A GhoshAbstract:The intrinsic irreversible Strain Limit eirr,0 of Nb3Sn superconducting wires, made by the restacked-rod process and doped with either Ti or Ta, undergoes a precipitous change as a function of temperature θ of the final heat-treatment for forming the A15 phase. Nb3Sn transitions from a highly brittle state where it cracks as soon as it is subjected to an axial tensile Strain of any measurable amount, to a state more resilient to tensile Strain as high as 0.4%. The remarkable abruptness of this transition (as most of it occurs over a range of only 10 °C) could pose real challenges for the heat-treatment of large magnets, such as those fabricated for the high-luminosity upgrade of the Large Hadron Collider (LHC). We named this behavior the Strain irreversibility cliff (SIC) to caution magnet developers. The approach to fulfilling application requirements just in terms of the conductor’s residual resistivity ratio RRR and critical-current density Jc is incomplete. Along with RRR and Jc wire specifications, and sub-element size requirements that reduce wire magnetization and instabilities effects, SIC imposes additional conStraints on the choice of heat-treatment conditions to ensure mechanical integrity of the conductor.
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influence of the heat treatment conditions microchemistry and microstructure on the irreversible Strain Limit of a selection of ti doped internal tin nb3sn iter wires
Superconductor Science and Technology, 2014Co-Authors: Najib Cheggour, Loren F Goodrich, Jolene D Splett, Theodore C Stauffer, P J Lee, Zu Hawn Sung, M C JewellAbstract:Systematic studies of the intrinsic irreversible Strain Limit eirr,0, microstructure, and microchemistry were made on several internal-tin Nb3Sn pre-production wires, fabricated for the domestic agencies of the USA and China participating in the International Thermonuclear Experimental Reactor. These wires were produced by Luvata, Oxford Superconducting Technology (OST), and Western Superconducting Technologies (WST), and were intended for the tokamak's toroidal-field coils. The results of this study show that, for a final heat-treatment at 650 °C to form the A15 phase, both eirr,0 and the de-pinning field Bc2* improved by increasing heat-treatment duration beyond 100 h for the Luvata wires. On the other hand, we saw no improvement in these two parameters as a function of heat-treatment duration in the OST wires. Furthermore, micro-chemical analysis of OST wires revealed that some Nb3Sn filaments have a Sn- and Ti-rich phase at the interface between Cu(Sn) matrix and Nb3Sn in the form of a shell around individual filaments. This phase is far less prominent in the Luvata and WST conductors, and could inhibit diffusion of Sn and Ti into Nb3Sn filaments during the reaction and may potentially be the reason for the lack of noticeable change in Bc2* with heat-treatment duration in the OST wires. The increase of eirr,0 and Bc2* with heat-treatment duration in the Luvata wires and the lack of increase in the OST wires may suggest a possible correlation between eirr,0 and the stoichiometry of the A15 composition. Investigation of the samples' microstructure revealed only a small number of cracked Nb3Sn filaments despite the significant and permanent degradation of their critical current Ic when subjected to longitudinal tensile Strain e beyond eirr,0. The scarcity of cracks indicate that Ic(e) measurements are highly sensitive to crack formation in Nb3Sn filaments, especially at low electric-field criteria 0.1 μV cm−1, even when the sizes of the individual filaments are only few micrometers. All the strands contained substantial Kirkendall porosity, but we found that the quantity and distribution of the Kirkendall voids vary significantly with strand design. Luvata wires have the least porosity, followed by WST wires, and then by OST strands. However, even though the presence of cracks in the Nb3Sn filaments that are in close proximity to Kirkendall voids suggest a correlation between crack initiation and the proximity of the filaments to these voids, the porosity investigation established no definitive relationship between porosity and eirr,0 in the wires studied.
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method for determining the irreversible Strain Limit of nb3sn wires
Superconductor Science and Technology, 2011Co-Authors: Loren F Goodrich, N Cheggour, Jolene D Splett, Theodore C Stauffer, Bernard J FillaAbstract:We define a rigorous and reliable method for determining the irreversible Strain Limit of Nb3Sn wires. The critical current (Ic) is measured as a function of applied longitudinal Strain (e), Ic(e), at one magnetic field and a temperature of 4.0 K. The sample is loaded and partially unloaded at progressively higher Strain levels to determine the irreversible Strain Limit, eirr, which is defined as the maximum loaded Strain where Ic is still reversible. Our method uses a polynomial fit of the loaded Ic(e) to derive the Ic residuals for the loaded and unloaded points that are analyzed to determine the Limit of irreversibility. The effect of varying the amount of Strain unloading is also studied. The possibility and problems of using the Strain dependent n-value (which indicates the steepness of the electric field–current, E–I, curve) to determine eirr are discussed. The method presented here to determine eirr has proven to be repeatable for many types of commercial Nb3Sn wires. This method can also be more generally used to determine eirr for any brittle low-temperature or high-temperature superconducting material.
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influence of ti and ta doping on the irreversible Strain Limit of ternary nb3sn superconducting wires made by the restacked rod process
Superconductor Science and Technology, 2010Co-Authors: Loren F Goodrich, N Cheggour, Jolene D Splett, Theodore C Stauffer, A Ghosh, G AmbrosioAbstract:Nb3Sn superconducting wires made by the restacked-rod process (RRP®) were found to have a dramatically improved resilience to axial tensile Strain when alloyed with Ti as compared to Ta. Whereas Ta-alloyed Nb3Sn in RRP wires showed permanent damage to its current-carrying capacity (Ic) when tensioned beyond an intrinsic Strain as small as 0.04%, Ti-doped Nb3Sn in RRP strands exhibits a remarkable reversibility up to a tensile Strain of about 0.25%, conceivably making Ti-doped RRP wires more suitable for the high field magnets used in particle accelerators and nuclear magnetic resonance applications where mechanical forces are intense. A Strain cycling experiment at room temperature caused a significant drop of Ic in Ta-alloyed wires, but induced an increase of Ic in the case of Ti-doped strands. Whereas either Ti or Ta doping yield a similar enhancement of the upper critical field of Nb3Sn, the much improved mechanical behavior of Ti-alloyed wires possibly makes Ti a better choice over Ta, at least for the RRP wire processing technique.