Effects of processing history on the evolution of surface damage layer and dislocation substructure in large grain niobium cavities
Abstract
Large grain niobium (Nb) is being investigated for fabricating superconducting radiofrequency cavities as an alternative to the traditional approach using fine grain polycrystalline Nb sheets. Past studies have identified a surface damage layer on fine grain cavities due to deep drawing and demonstrated the necessity for chemical etching on the surface. However, the origin of and depth of the damage layer are not well understood, and similar exploration on large grain cavities is lacking. In this work, electron backscatter diffraction (EBSD) was used to examine the cross sections at the equator and iris of a half cell deep drawn from a large grain Nb ingot slice. The results indicate that the damage (identified by a high density of geometrically necessary dislocations) depends on crystal orientations, is different at the equator and iris, and is present through the full thickness of a half cell in some places. After electron backscatter diffraction, the specimens were heat treated at 800 °C or 1000 °C for two hours, and the same areas were reexamined. A more dramatic decrease in dislocation content was observed at the iris than the equator, where some regions exhibited no change. The specimens were then etched and examined again, tomore »
- Authors:
- Publication Date:
- Research Org.:
- Michigan State Univ., East Lansing, MI (United States)
- Sponsoring Org.:
- USDOE Office of Science (SC)
- OSTI Identifier:
- 1229916
- Alternate Identifier(s):
- OSTI ID: 1240125
- Grant/Contract Number:
- SC0009962
- Resource Type:
- Published Article
- Journal Name:
- Physical Review Special Topics. Accelerators and Beams
- Additional Journal Information:
- Journal Name: Physical Review Special Topics. Accelerators and Beams Journal Volume: 18 Journal Issue: 12; Journal ID: ISSN 1098-4402
- Publisher:
- American Physical Society
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
Citation Formats
Kang, D., Bieler, T. R., and Compton, C. Effects of processing history on the evolution of surface damage layer and dislocation substructure in large grain niobium cavities. United States: N. p., 2015.
Web. doi:10.1103/PhysRevSTAB.18.123501.
Kang, D., Bieler, T. R., & Compton, C. Effects of processing history on the evolution of surface damage layer and dislocation substructure in large grain niobium cavities. United States. https://doi.org/10.1103/PhysRevSTAB.18.123501
Kang, D., Bieler, T. R., and Compton, C. Wed .
"Effects of processing history on the evolution of surface damage layer and dislocation substructure in large grain niobium cavities". United States. https://doi.org/10.1103/PhysRevSTAB.18.123501.
@article{osti_1229916,
title = {Effects of processing history on the evolution of surface damage layer and dislocation substructure in large grain niobium cavities},
author = {Kang, D. and Bieler, T. R. and Compton, C.},
abstractNote = {Large grain niobium (Nb) is being investigated for fabricating superconducting radiofrequency cavities as an alternative to the traditional approach using fine grain polycrystalline Nb sheets. Past studies have identified a surface damage layer on fine grain cavities due to deep drawing and demonstrated the necessity for chemical etching on the surface. However, the origin of and depth of the damage layer are not well understood, and similar exploration on large grain cavities is lacking. In this work, electron backscatter diffraction (EBSD) was used to examine the cross sections at the equator and iris of a half cell deep drawn from a large grain Nb ingot slice. The results indicate that the damage (identified by a high density of geometrically necessary dislocations) depends on crystal orientations, is different at the equator and iris, and is present through the full thickness of a half cell in some places. After electron backscatter diffraction, the specimens were heat treated at 800 °C or 1000 °C for two hours, and the same areas were reexamined. A more dramatic decrease in dislocation content was observed at the iris than the equator, where some regions exhibited no change. The specimens were then etched and examined again, to determine if the subsurface region behaved differently than the surface. As a result, little change in the dislocation substructure was observed, suggesting that the large grain microstructure is retained with a normal furnace anneal.},
doi = {10.1103/PhysRevSTAB.18.123501},
journal = {Physical Review Special Topics. Accelerators and Beams},
number = 12,
volume = 18,
place = {United States},
year = {Wed Dec 16 00:00:00 EST 2015},
month = {Wed Dec 16 00:00:00 EST 2015}
}
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https://doi.org/10.1103/PhysRevSTAB.18.123501
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