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Title: Correlation of filament distortion and RRR degradation in drawn and rolled PIT and RRP Nb 3 Sn wires

PIT and RRP® Nb3Sn strands are being developed for high field accelerator magnet upgrades for the high luminosity LHC. Here we report a quantitative study of the shape and position of PIT filaments and RRP® sub-elements after rolling lengths of unreacted PIT and RRP® round wires to simulate cabling deformation. In the as-drawn condition, filament shape distortion occurs preferentially in the outer ring filaments. By contrast, rolling induces non-uniform shear bands that generate greater distortion of inner ring filaments. By making a full digitization of the shapes of all filaments, we find that a critical distortion occurs for thickness reductions between 10% and 20% when filament shapes in inner filament rings heavily degrade, especially in the vicinity of the strong 45° shear bands imposed by the rolling. It is well known that maintaining diffusion barrier integrity is vital to retaining adequate RRR in the stabilizing copper needed for magnet stability. Diffusion barrier breaks occur preferentially in these distorted inner filaments and drive local Sn leakage during reaction, increasing RRR degradation.
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [1] ;  [1]
  1. Florida State Univ., Tallahassee, FL (United States)
  2. Florida State Univ., Tallahassee, FL (United States). Dept. of Mechanical Engineering
Publication Date:
OSTI Identifier:
1312798
Grant/Contract Number:
SC0012083
Type:
Accepted Manuscript
Journal Name:
Superconductor Science and Technology
Additional Journal Information:
Journal Volume: 29; Journal Issue: 8; Conference: Mechanical and Electromagnetic Properties of Composite Superconductors (MEM 2016) Tallahassee, FL 03/21 - 03/23, Tallahassee, FL (United States), 21-23 Mar 2016; Journal ID: ISSN 0953-2048
Publisher:
IOP Publishing
Research Org:
Florida State Univ., Tallahassee, FL (United States). Applied Superconductivity Center (ASC), National High Magnetic Field Laboratory (HNMFL)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE superconductor, Nb3Sn, deformation, residual resistance ratio, powder in tube, rod restack process