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Effect of ECAP on Change in Microstructure and Critical Current Density of Low Temperature Super-Conducting Monowire

  • Seon-Myung Park
  • Young-Seok Oh
  • Se-Jong Kim
  • Hee Rak Kim
  • Howon Lee
  • In Yong Moon
  • Duck-Young Hwang
  • Seong-Hoon KangEmail author
Regular Paper
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Abstract

The critical current density (Jc), which is a major performance parameter of low temperature superconducting Nb-46.5 wt%Ti wire, can be improved by uniformly dispersed fine α-Ti precipitates since they serve as a flux pinning center. The high volume fraction of α-Ti precipitates at grain boundary intersections can be achieved by repetitive large deformation and intermediate heat treatments. For this aim, we investigated effect of severe plastic deformation of Nb-46.5 wt%Ti billet on the changes in microstructure and Jc by assigning equal channel angular process (ECAP) followed by groove rolling and drawing. In addition, intermediate heat treatments with different heating condition and holding time after each process were assigned to precipitate the fine α-Ti. It was observed that the curled flow lines like shear bands with the highly dense dislocations were formed after ECAP leading to recrystallization and the high volume fraction of α-Ti after subsequent heat treatment. The additional plastic deformation by groove rolling and drawing increased the volume fraction of the α-Ti and the aspect ratio of its shape. As a result, the critical current density at the lower range of magnetic field was enhanced with increasing the number of ECAP pass.

Keywords

Nb-46.5wt %Ti monowire ECAP Groove rolling Drawing Heat treatment Volume fraction of α-Ti Critical current density 

List of symbols

A

Long diameter of groove rolls (mm)

Γ

Approach angle (o)

Ao

Initial area of the billet (mm2)

Ad

Deformed area of the billet (mm2)

B

Short diameter of groove rolls (mm)

Bc

Route with rotation angle 90o in each pass of ECAP

deff

Effective area of superconducting NbTi material (mm)

D1

Inlet diameter in drawing die (mm)

D2

Outlet diameter in drawing die (mm)

Ε

Accumulated strain in groove rolling and drawing

εN

Accumulated strain in ECAP

Jc

Critical current density (A/cm2)

L

Approach length in drawing die (mm)

∆M

Magnetization loop (emu/cm3)

N

Number of pass in ECAP

R

Reduction ratio (%)

Φ

Inner angle of ECAP die (o)

Ψ

Corner angle of ECAP die (o)

Shape factor

Notes

Acknowledgements

This work was supported by Industrial Technology Innovation Program (No.: 10053590) funded by the Ministry of Trade, Industry and Energy (MOTIE), Korea.

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Copyright information

© Korean Society for Precision Engineering 2019

Authors and Affiliations

  • Seon-Myung Park
    • 1
  • Young-Seok Oh
    • 2
  • Se-Jong Kim
    • 2
  • Hee Rak Kim
    • 2
  • Howon Lee
    • 2
  • In Yong Moon
    • 2
  • Duck-Young Hwang
    • 3
  • Seong-Hoon Kang
    • 2
    Email author
  1. 1.Technology of Material Science(TOMS)SacheonRepublic of Korea
  2. 2.Korea Institute of Materials ScienceChangwonRepublic of Korea
  3. 3.Kiswire Advanced Technology Co., LtdDaejeonRepublic of Korea

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