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Title: Effects of processing history on the evolution of surface damage layer and dislocation substructure in large grain niobium cavities

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 » 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.« less
Authors:
 [1] ;  [1] ;  [2]
  1. Michigan State Univ., East Lansing, MI (United States)
  2. Facility for Rare Isotope Beams, East Lansing, MI (United States)
Publication Date:
OSTI Identifier:
1229916
Grant/Contract Number:
SC0009962
Type:
Published Article
Journal Name:
Physical Review Special Topics. Accelerators and Beams
Additional Journal Information:
Journal Volume: 18; Journal Issue: 12; Journal ID: ISSN 1098-4402
Publisher:
American Physical Society (APS)
Research Org:
Michigan State Univ., East Lansing, MI (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English