http://www.surfacetreatments.it/thinfilms RRR Niobium Seamless Cavities (Roy Crooks - 20') Speaker: Roy Crooks - Black Laboratories | Duration: 20 min. Abstract Roy Crooks, Black Laboratories, L.L.C., Newport News, VA, USA Waldemar Singer, DESY, Hamburg, Germany Conventional welding of half-cells deep-drawn from niobium sheet may generate flaws near the cavity equators which limit cavity performance. Cavities have been produced from RRR niobium tube by a combination of spinning and hydroforming, using the facilities at DESY. Seamless cavities were manufactured from tubes produced by two different methods, based on pipe spun from plate and on pipe back-extruded from ingot (at ATI Wah Chang). The microstructures resulting from the two fabrication methods are described, along with SRF properties from recent tests on prototype ILC cavities.

1. RRR Niobium Seamless Cavities
Roy Crooks1
Waldemar Singer2
1Black Laboratories, L.L.C., Newport News, Virginia, U.S.A.
2Deutsches Elektronen‐Synchrotron (DESY), Hamburg, Germany
The Fourth International Workshop on
THIN FILMS AND NEW IDEAS FOR
PUSHING THE LIMITS OF RF SUPERCONDUCTIVITY
October 4 – 6, 2010
Legnaro National Laboratories, Padua, Italy
Support for R. Crooks under DOE SBIR Grant No. DE‐FG02‐04ER83909, and from Fermilab and Jefferson Lab

2. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
Rationale and Approach, applications for ILC 1.3 GHz SRF Cavities
Advantages of seamless tube cavity production
• No RRR degradation in the welding seam
• No pits associated with the HAZ
• No weld contamination
• Lower production costs in large production runs
• Less scatter in performance compared to welded cavities
Approach:
Seamless tubes produced by:
• Drawing or Spinning from sheet and flow forming (DESY)
• Extrusions were not adequate due to large grain size
• Heavily deformed and recrystallized fine‐grain billet, Back extrusion,
forward extrusion and flow‐forming (BL/AWC)
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3. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
Tube Making Necking Hydroforming
W. Singer, DESY
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4. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
DESY: Tube Making from sheet
Successful fabrication
of tube and hydroformed
cavities
Tube is good for 3‐cells
W. Singer, DESY
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5. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
DESY: Necking by Profile Ring
W. Singer, DESY
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6. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
DESY: Hydroforming
W. Singer, DESY
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7. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
DESY: Assembled 3x3‐cell ILC Cavity
W. Singer, DESY
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8. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
BL/AWC
Extruded Tube
Advantages:
• The metal is exposed to steady‐state conditions for most of
the extrusion length.
• Results in a uniform structure and axisymmetric properties.
Requires a billet with a fine‐grain, randomly oriented starting
microstructure.
Tubes shaped at DESY by spinning and hydroforming.
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9. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
Billet Processing Results (3 deformation methods)
50 mm diameter sub‐scale billet, Inverse Pole Figures of radial sections,
grain boundary number fraction vs. misorientation, texture intensity
a surface t/4 t/2 surface t/4 t/2 b
Scaled
up to
165 mm
c surface t/4 t/2 Misorientation Angle Misorientation Angle
0.07
a 0.07
b
0.06 0.06
0.05 0.05
Number Fraction
Number Fraction
0.04 0.04
0.03 0.03
0.02 0.02
0.01 0.01
0.00 0.00
10 20 30 40 50 60 10 20 30 40 50 60
Misorientation Angle [degrees] Misorientation Angle [degrees]
Misorientation Angle from t/4
0.07
0.06
c Texture Intensity vs. Distance from Surface,
inches
0.05
25
Number Fraction
0.04
20
0.03 Texture 15
Intensity 0
ODF Max 10
0.02
0.25
0.01 5 0.5
0.00 0
10 20 30 40 50 60
A B C
Misorientation Angle [degrees]
Process
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10. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
BL/AWC Tube Processing & Testing
Flow Forming Thickness Recrystallization
14 μm
ODF
max 7
Misorientation Angle
0.13
0.12
Mackenzie (random)
0.11
0.10
0.09
0.08
Number Fraction
0.07
0.06
B2B 0.05
0.04
B1C B1B 0.03
0.02
0.01
0.00
0 10 20 30 40 50 60 70
90% Rx
Misorientation Angle [degrees]
Rx Rx Rx Correlated Random
Tensile Tests/ Roughening Formability Test Hall-Petch
DESY Limiting dome height test YS, MPa vs 1/sqrt(d)
from flattened tube
50-60% elongattion
100mm dome 100
B1B 40% needed 5mm/min
90
BL/AWC
Y ,M a
80
S P
70
Huang and Cao
Northwestern University 60
November 2009
50
0 0.1 0.2 0.3
Inve rs e s quare root of (d)
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11. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
BL/AWC Tube (B2B) Forming at DESY
December 2009
Spinning Hydroforming
Final Hydroforming
Stage
Spinning of irises First Stage Second Stage
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12. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
BL/AWC Hydroforming Results at DESY
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13. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
DESY Coarse Grain SRF Test 3‐cell BL/AWC Fine Grain SRF Test 3‐cell
at JLab (Peter Kneisel) at JLab (Peter Kneisel)
(9‐cell testing has started at DESY) (9‐cell prepped for testing at JLab)
3-cell seamless cavity #3, Test #1
1.0E+11
1.0E+10
Q0
Q-drop. No quench
1.0E+09
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
Eacc [MV/m]
Superfluid Helium leak
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14. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
Assembly of BL/AWC 9‐cell
(best of lot)
Welded, stiffener rings
BCP, no leaks warm or cold
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15. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
Remaining Issues
• Optimum Grain Size
– Small for smoothness
– Larger for more elongation? (we are forming near the ductility limit
for Nb)
• Optimum Crystallographic Texture
– What target other than random? (guidelines from bcc sheet forming?)
– Changes with higher T anneal
• Intermediate Anneals (work to‐date has been at RT)?
– During flow‐forming of tube
– During spinning/hydroforming of cavities
• Increase total elongation
• Modification of hydroforming approach (Bob Rimmer, JLab)
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16. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
Grain size optimum?
Smoother surface vs. lower ductility
Hall-Petch Plot
YS, MPa vs 1/sqrt(d)
100
90
Y ,M a
80
S P
70
60
50
0 0.1 0.2 0.3
Inve rs e s quare root of (d)
AA7075
Coarse vs fine grain Nb tube Zhao et al Act mater; 52 (2004) 4859
YS vs inverse sq rt grain size
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17. RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010
Summary
• Nine‐cell ILC geometry ILC cavities can be assembled from seamless tube
given room temperature necking and hydroforming procedures used at
DESY.
• The tube from spinning or deep‐drawing requires a 3x3 cell assembly, with
iris welds between 3‐cell sections.
• Heavily deformed and recrystallized billet has been shown to allow
production of a fine‐grain, weakly textured tube.
• The BL/AWC fine‐grain extruded tube is capable of fabrication into a 9‐cell
cavity without welds, although the proper machine will have to be built.
• The consistent microstructure of the fine‐grain extruded tube should
reduce the scatter in srf performance with production scale operations.
• Tube process optimization studies are in progress.
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