Author: Thune, Z.L.
Paper Title Page
MOPMB041 Microstructure Development in a Cold Worked SRF Niobium Sheet After Heat Treatments 191
 
  • S. Balachandran, P. Dhakal, A-M. Valente-Feliciano
    JLab, Newport News, Virginia, USA
  • T.R. Bieler
    Michigan State University, East Lansing, Michigan, USA
  • S. Chetri, P.J. Lee
    NHMFL, Tallahassee, Florida, USA
  • Z.L. Thune
    MSU, East Lansing, USA
 
  Funding: Jefferson Science Associates, LLC under U.S. DOE Grant DEAC05-06OR23177, U.S. DOE, Office of HEP under Grant DE-SC0009960, and NHMFL through NSF Grant DMR-1644779 and the State of Florida.
Bulk Nb for TESLA shaped SRF cavities is a mature technology. Significant advances are in order to push Q0’s to 1010-11(T= 2K), and involve modifications to the sub-surface Nb layers by impurity doping. In order to achieve the lowest surface resistance any trapped flux needs to be expelled for cavities to reach high Q0’s. There is clear evidence that cavities fabricated from polycrystalline sheets meeting current specifications require higher temperatures beyond 800 °C leads to better flux expulsion, and hence improves Q0. Recently, cavities fabricated with a non-traditional Nb sheet with initial cold work due to cold rolling expelled flux better after 800 °C/3h heat treatment than cavities fabricated using fine-grain poly-crystalline Nb sheets. Here, we analyze the microstructure development in Nb from the vendor supplied cold work non- annealed sheet that was fabricated into an SRF cavity as a function of heat treatment building upon the methodology development to analyze microstructure being developed by the FSU-MSU-UT, Austin-JLAB collaboration. The results indicate correlation between full recrystallization and better flux expulsion.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB041  
About • Received ※ 19 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 09 July 2023
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WEPWB116 The Influence of Sample Preparation, Soak Time, and Heating Rate on Measured Recrystallization of Deformed Polycrystalline Niobium 863
 
  • Z.L. Thune
    MSU, East Lansing, USA
  • T.R. Bieler
    Michigan State University, East Lansing, Michigan, USA
 
  Funding: DOE/OHEP (Grant Number: DE-SC0009960)
Improving accelerator performance relies on consistent production of high-purity niobium superconducting radiofrequency (SRF) cavities. Current production uses an 800 °C 3 hr heat treatment, but 900-1000 °C can improve cavity performance via recrystallization (Rx) and grain growth. As Rx is thermally activated, increasing the temperature and/or the heating rate could facilitate a reduction in geometrically necessary dislocation (GND) density that is associated with the degradation of cavity performance via trapped magnetic flux. Recent work shows that increasing the annealing temperature increased the Rx fraction in cold-rolled polycrystalline niobium. However, the influence of heating rate on the extent of Rx was minimal with a 3 hr soak time. To further assess the influence of heating rate on measured Rx, as well as the effects of sample preparation, electron backscatter diffraction (EBSD) was used to quantify the extent of Rx on samples annealed at a single temperature with different soak times. Comparing samples with different surface preparation shows that pinned grain boundaries on the free surface reveal a much smaller grain size than below the surface.
* Z.L. Thune et al., "The Influence of Strain Path and Heat Treatment Variations on Recrystallization in Cold-Rolled High-Purity Niobium Polycrystals," doi: 10.1109/TASC.2023.3248533.
 
poster icon Poster WEPWB116 [1.312 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB116  
About • Received ※ 23 June 2023 — Revised ※ 26 June 2023 — Accepted ※ 20 August 2023 — Issue date ※ 21 August 2023
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)