Crooks - Seamless cavities

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 onTHIN FILMS AND NEW IDEAS FOR

PUSHING THE LIMITS OF RF SUPERCONDUCTIVITYOctober 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

RRR Niobium Seamless Cavities; Crooks, Singer TFSRF 2010, Legnaro, October 4 – 6, 2010

2

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)

Rationale and Approach, applications for ILC 1.3 GHz SRF Cavities


3

W. Singer, DESY

Tube Making Necking Hydroforming


4

Successful fabricationof tube and hydroformedcavities

Tube is good for 3‐cells

W. Singer, DESY

DESY: Tube Making from sheet


5

W. Singer, DESY

DESY: Necking by Profile Ring


6

W. Singer, DESY

DESY: Hydroforming


7

W. Singer, DESY

DESY: Assembled 3x3‐cell ILC Cavity


8

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.

BL/AWC


9

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

surface t/4 t/2c

surface t/4 t/2 bsurface t/4 t/2a

Scaled

up to

165 mm

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

10 20 30 40 50 60

Num

ber F

ract

ion

Misorientation Angle [degrees]

Misorientation Angle

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

10 20 30 40 50 60

Num

ber F

ract

ion



0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

10 20 30 40 50 60

Num

ber F

ract

ion



a

c

b

05

10152025

Texture IntensityODF Max

A B CProcess

Texture Intensity vs. Distance from Surface, inches

00.250.5

from t/4


10

BL/AWC Tube Processing & TestingThicknessFlow Forming

RxRxRx

B1BB2B

B1C

YS, MPa vs 1/sqrt(d)

50

60

70

80

90

100

0 0.1 0.2 0.3

Inverse square root of (d)

YS, M

Pa

Hall-Petch

Limiting dome height testfrom flattened tube100mm dome5mm/min

Huang and CaoNorthwestern UniversityNovember 2009

Tensile Tests/ Roughening

DESY

BL/AWCB1B

50-60% elongattion40% needed

90% Rx

Recrystallization

14 μmODF max 7

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

0 10 20 30 40 50 60 70

Num

ber F

ract

ion



Correlated Random

Mackenzie (random)

Formability Test


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BL/AWC Tube (B2B) Forming at DESY December 2009

Hydroforming

Final HydroformingStage

First Stage

Spinning

Spinning of irises Second Stage


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BL/AWC Hydroforming Results at DESY


13

DESY Coarse Grain SRF Test 3‐cell

at JLab (Peter Kneisel)

(9‐cell testing has started at DESY)

3-cell seamless cavity #3, Test #1

1.0E+09

1.0E+10

1.0E+11

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

Eacc [MV/m]

Q0

Q-drop. No quench

BL/AWC Fine Grain SRF Test 3‐cell

at JLab (Peter Kneisel)

(9‐cell prepped for testing at JLab)

Superfluid

Helium leak


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Assembly of BL/AWC 9‐cell (best of lot)

Welded, stiffener ringsBCP, no leaks warm or cold


15

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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Grain size optimum? Smoother surface vs. lower ductility

YS, MPa vs 1/sqrt(d)

50

60

70

80

90

100

0 0.1 0.2 0.3

Inverse square root of (d)

YS, M

Pa

Hall-Petch Plot

AA7075Zhao et al Act mater; 52 (2004) 4859Coarse vs fine grain Nb tube

YS vs inverse sq rt grain size


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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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Crooks - Seamless cavities

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