Title: Development of low angle grain boundaries in lightly deformed superconducting niobium and their influence on hydride distribution and flux perturbation

Abstract

This study shows that low angle grain boundaries (LAGBs) can be created by small 5% strains in high purity (residual resistivity ratio ≥ 200) superconducting radio frequency (SRF)-grade single crystalline niobium (Nb) and that these boundaries act as hydrogen traps as indicated by the distribution of niobium hydrides (Nb1-xHx). Nb1-xHx is detrimental to SRF Nb cavities due to its normal conducting properties at cavity operating temperatures. By designing a single crystal tensile sample extracted from a large grain (>5 cm) Nb ingot slice for preferred slip on one slip plane, LAGBs and dense dislocation boundaries developed. With chemical surface treatments following standard SRF cavity fabrication practice, Nb_1-xH_x phases were densely precipitated at the LAGBs upon cryogenic cooling (8–10 K/min). Micro-crystallographic analysis confirmed heterogeneous hydride precipitation, which included significant hydrogen atom accumulation in LAGBs. Magneto-optical imaging analysis showed that these sites can then act as sites for both premature flux penetration and eventually flux trapping. However, this hydrogen related degradation at LAGBs did not completely disappear even after an 800 °C/2 h anneal typically used for hydrogen removal in SRF Nb cavities. These findings suggest that hydride precipitation at an LAGB is facilitated by a non-equilibrium concentration of vacancy-hydrogen (H) complexesmore » aided by mechanical deformation and the hydride phase interferes with the recovery process under 800 °C annealing.« less

Authors:

Sung, Z. -H. ^[1]; Wang, M. ^[2]; Polyanskii, A. A.  ^[1];

• Search DOE PAGES for author "Polyanskii, A. A."
• Search DOE PAGES for ORCID "0000-0002-5977-5324"

Santosh, C.  ^[1];

• Search DOE PAGES for author "Santosh, C."
• Search DOE PAGES for ORCID "0000-0003-0633-379X"

Balachandran, S.  ^[1];

• Search DOE PAGES for author "Balachandran, S."
• Search DOE PAGES for ORCID "0000-0002-0077-8504"

Compton, C. ^[3]; Larbalestier, D. C.  ^[1];

• Search DOE PAGES for author "Larbalestier, D. C."
• Search DOE PAGES for ORCID "0000-0001-7098-7208"

Bieler, T. R. ^[2]; Lee, P. J.  ^[1]

• Search DOE PAGES for author "Lee, P. J."
• Search DOE PAGES for ORCID "0000-0002-8849-8995"

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+ Show Author Affiliations

1. Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab. (MagLab). Applied Superconductivity Center
2. Michigan State Univ., East Lansing, MI (United States). Dept. of Mechanical Engineering
3. Michigan State Univ., East Lansing, MI (United States). Facility for Rare Isotope Beams

Publication Date:

Fri May 19 00:00:00 EDT 2017

Research Org.:

Florida State Univ., Tallahassee, FL (United States); Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), High Energy Physics (HEP); State of Florida (United States); National Science Foundation (NSF)

Contributing Org.:

Michigan State Univ., East Lansing, MI (United States)

OSTI Identifier:

1361685

Alternate Identifier(s):

OSTI ID: 1361680; OSTI ID: 1361893; OSTI ID: 1371587

Report Number(s):

FERMILAB-PUB-17-222-TD
Journal ID: ISSN 0021-8979

Grant/Contract Number:  

SC0009960; FG02-13ER41973; DMR-1157490; AC02-07CH11359

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Applied Physics

Additional Journal Information:

Journal Volume: 121; Journal Issue: 19; Journal ID: ISSN 0021-8979

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 43 PARTICLE ACCELERATORS; Niobium; Grain boundaries; Superconductivity; Magnetic flux; Dislocations