## Effect of the fabrication route on the phase and volume changes during the reaction heat treatment of Nb3Sn superconducting wires

2020
##### Authors
Scheuerlein, Christian
Andrieux, Jérôme
Michels, Matthias
Lackner, Friedrich
Chiriac, Rodica
Toche, François
Di Michiel, Marco
Journal article
Published
##### Published in
Superconductor Science and Technology ; 33 (2020), 3. - 034004. - Institute of Physics Publishing (IOP). - ISSN 0953-2048. - eISSN 1361-6668
##### Abstract
Accelerator magnets that can reach magnetic fields well beyond the Nb-Ti performance limits are presently being built and developed, using Nb3Sn superconductors. This technology requires reaction heat treatment (RHT) of the magnet coils, during which Nb3Sn is formed from its ductile precursor materials (a "wind and react" approach). The Nb3Sn microstructure and microchemistry are strongly influenced by the conductor fabrication route, and by the phase changes during RHT. By combining in situ differential scanning calorimetry, high energy synchrotron x-ray diffraction, and micro-tomography experiments, we have acquired a unique data set that describes in great detail the phase and microstructure changes that take place during the processing of restacked rod process (RRP), powder-in-tube (PIT), and internal tin (IT) Nb3Sn wires. At temperatures below 450 °C the phase evolutions in the three wire types are similar, with respectively solid state interdiffusion of Cu and Sn, Cu6Sn5 formation, and Cu6Sn5 peritectic transformation. Distinct differences in phase evolutions in the wires are found when temperatures exceed 450 °C. The volume changes of the conductor during RHT are a difficulty in the production of Nb3Sn accelerator magnets. We compare the wire diameter changes measured in situ by dilatometry with the phase and void volume evolution of the three types of Nb3Sn wire. Unlike the Nb3Sn wire length changes, the wire diameter evolution is characteristic for each Nb3Sn wire type. The strongest volume increase, of about 5%, is observed in the RRP wire, where the main diameter increase occurs above 600 °C upon Nb3Sn formation.
530 Physics
##### Keywords
Nb3Sn, microstructure, phase transformations, volume changes, x-ray diffraction, differential scanning calorimetry, synchrotron micro-tomography
##### Cite This
ISO 690SCHEUERLEIN, Christian, Jérôme ANDRIEUX, Matthias MICHELS, Friedrich LACKNER, Christian MEYER, Rodica CHIRIAC, François TOCHE, Matthias HAGNER, Marco DI MICHIEL, 2020. Effect of the fabrication route on the phase and volume changes during the reaction heat treatment of Nb3Sn superconducting wires. In: Superconductor Science and Technology. Institute of Physics Publishing (IOP). 33(3), 034004. ISSN 0953-2048. eISSN 1361-6668. Available under: doi: 10.1088/1361-6668/ab627c
BibTex
@article{Scheuerlein2020-03-01Effec-50549,
year={2020},
doi={10.1088/1361-6668/ab627c},
title={Effect of the fabrication route on the phase and volume changes during the reaction heat treatment of Nb<sub>3</sub>Sn superconducting wires},
number={3},
volume={33},
issn={0953-2048},
journal={Superconductor Science and Technology},
author={Scheuerlein, Christian and Andrieux, Jérôme and Michels, Matthias and Lackner, Friedrich and Meyer, Christian and Chiriac, Rodica and Toche, François and Hagner, Matthias and Di Michiel, Marco},
note={Article Number: 034004}
}

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<dcterms:abstract xml:lang="eng">Accelerator magnets that can reach magnetic fields well beyond the Nb-Ti performance limits are presently being built and developed, using Nb&lt;sub&gt;3&lt;/sub&gt;Sn superconductors. This technology requires reaction heat treatment (RHT) of the magnet coils, during which Nb&lt;sub&gt;3&lt;/sub&gt;Sn is formed from its ductile precursor materials (a "wind and react" approach). The Nb&lt;sub&gt;3&lt;/sub&gt;Sn microstructure and microchemistry are strongly influenced by the conductor fabrication route, and by the phase changes during RHT. By combining in situ differential scanning calorimetry, high energy synchrotron x-ray diffraction, and micro-tomography experiments, we have acquired a unique data set that describes in great detail the phase and microstructure changes that take place during the processing of restacked rod process (RRP), powder-in-tube (PIT), and internal tin (IT) Nb&lt;sub&gt;3&lt;/sub&gt;Sn wires. At temperatures below 450 °C the phase evolutions in the three wire types are similar, with respectively solid state interdiffusion of Cu and Sn, Cu&lt;sub&gt;6&lt;/sub&gt;Sn&lt;sub&gt;5&lt;/sub&gt; formation, and Cu&lt;sub&gt;6&lt;/sub&gt;Sn&lt;sub&gt;5&lt;/sub&gt; peritectic transformation. Distinct differences in phase evolutions in the wires are found when temperatures exceed 450 °C. The volume changes of the conductor during RHT are a difficulty in the production of Nb&lt;sub&gt;3&lt;/sub&gt;Sn accelerator magnets. We compare the wire diameter changes measured in situ by dilatometry with the phase and void volume evolution of the three types of Nb&lt;sub&gt;3&lt;/sub&gt;Sn wire. Unlike the Nb&lt;sub&gt;3&lt;/sub&gt;Sn wire length changes, the wire diameter evolution is characteristic for each Nb&lt;sub&gt;3&lt;/sub&gt;Sn wire type. The strongest volume increase, of about 5%, is observed in the RRP wire, where the main diameter increase occurs above 600 °C upon Nb&lt;sub&gt;3&lt;/sub&gt;Sn formation.</dcterms:abstract>
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Yes
Yes