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Title: Characterization of the Formability of High-Purity Polycrystalline Niobium Sheets for Superconducting Radiofrequency Applications

Journal Article · · Journal of Engineering Materials and Technology
DOI: https://doi.org/10.1115/1.4052557 · OSTI ID:1893870
 [1];  [2];  [3];  [4];  [5];  [3];  [2]
  1. I-Cube Research/Bmax (France); ENSTA Bretagne (France); Centre National de la Recherche Scientifique-Mixed Organizations (CNRS-UMR), Paris (France); Research Institute Dupuy De Lôme (IRDL) (France)
  2. Universite de Lorraine, Champenoux (France); Centre National de la Recherche Scientifique-Mixed Organizations (CNRS-UMR), Paris (France); Arts et Métiers ParisTech (France)
  3. I-Cube Research/Bmax (France)
  4. European Organization for Nuclear Research (CERN), Geneva (Switzerland)
  5. ENSTA Bretagne (France); Centre National de la Recherche Scientifique-Mixed Organizations (CNRS-UMR), Paris (France); Research Institute Dupuy De Lôme (IRDL) (France)
+ Show Author Affiliations

The forming limit diagram (FLD) of high-purity niobium sheets used for the manufacturing of superconducting radiofrequency (SRF) cavities is presented. The Marciniak (in-plane) test was used with niobium blanks with a thickness of 1 mm and blank carriers of annealed oxygen-free electronic (OFE) copper. A high formability was measured, with an approximate true major strain at necking for plane strain of 0.44. The high formability of high-purity niobium is likely caused by its high strain rate sensitivity of 0.112. Plastic strain anisotropies (r-values) of 1.66, 1.00, and 2.30 were measured in the 0 deg, 45 deg, and 90 deg directions. However, stress–strain curves at a nominal strain rate of ~10–3 s–1 showed similar mechanical properties in the three directions. Theoretical calculations of the forming limit curves (FLCs) were conducted using an analytical two-zone model. The obtained results indicate that the anisotropy and strain rate sensitivity of niobium affect its formability. The model was used to investigate the influence of strain rate on strains at necking. The obtained results suggest that the use of high-speed sheet forming should further increase the formability of niobium.

Research Organization:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC); European Union (EU)
Grant/Contract Number:
AC02-05CH11231
OSTI ID:
1893870
Journal Information:
Journal of Engineering Materials and Technology, Journal Name: Journal of Engineering Materials and Technology Journal Issue: 2 Vol. 144; ISSN 0094-4289
Publisher:
ASMECopyright Statement
Country of Publication:
United States
Language:
English

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mechanical behavior
36 MATERIALS SCIENCE
Marciniak test
SRF
anisotropy
blanks
forming limit diagram
forming limit diagrams
manufacturing
mechanical properties
metals
modeling
necking
niobium
plane strain
plastic behavior
two-zone model