Tensile Properties of 304 S.S.

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Update on Helium Retention Behavior in Tungsten
D. Forsythe,1 S. Gidcumb,1 S. Gilliam,1 N.
Hashimoto 2, J. D. Hunn,2 G. Lamaze, 3 N.
Parikh,1 S. J. Zinkle2, L. Snead2 1 Dept. of
Physics and Astronomy, UNC-Chapel Hill, Chapel
Hill, NC 2 Oak Ridge National Laboratory, Oak
Ridge, TN 3 National Institute of Standards and
Technology, Gaithersburg, MD
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As-rolled Powder Metallurgy W
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Powder Met W annealed at 1000C for 1 hr
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Powder Met W annealed at 1200C for 1 hr
Planimetric procedure (ASTM Designation E112-96)
Number of Grains, NA (/mm2) 11911
Average Grain Area, A 1/ NA 84 (?m2)
Average Diameter, d v(1/ NA) 9.2 (?m)
ASTM Grain Size , G (3.321928 log10 NA) -
2.954 10.6
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Powder Met W annealed at 1300C for 1 hr
Planimetric procedure (ASTM Designation E112-96)
Number of Grains, NA (/mm2) 8336
Average Grain Area, A 1/ NA 119 (?m2)
Average Diameter, d v(1/ NA) 11.0 (?m)
ASTM Grain Size , G (3.321928 log10 NA) -
2.954 10.1
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Summary of Powder metallurgy W annealing results
Grain number, NA (mm-2) Ave. Grain Area, A (?m2) Ave. Grain diameter, d (?m) ASTM Grain Size , G
Annealed at 1200C for 1 hr 11911 84 10.6 10.6
Annealed at 1200C for 2 hrs 6222 161 12.7 9.6
Annealed at 1200C for 5 hrs 4088 245 15.6 9.0
Annealed at 1300C for 1 hr 8336 119 11.0 10.1
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Recrystallization in Powder Metallurgy W
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At room temp. growth of He bubbles beneath the
surface causes blistering at 3 x 1021/m2 and
surface exfoliation at 1022/m2. For IFE power
plant, MeV He dose gtgtgt 1022/m2 .

First Wall Armor
MeV Helium
vacancy
MeV Helium
0 1 2 3 4 5 6
7 8 9 10
Time of microseconds
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AFM of blistering

• Topographical AFM image of surface blisters on
  polycrystalline tungsten
• Blister caps are 1.9 ?m tall comparable to
  helium implant depth

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Direction of Research Over Past Year

• Complete study of stepwise dose annealing.
  Automate system for very large dose(gt1019 n/m2)
  and higher (gt2000C.)

Single Crystal W
Total Dose ? 1E19 3E19 5E19 1E20
Dose/Step ? 100 (1) 100 (1) 100 (1) 100 (1)
1E18 85 (10)
1E17 65 (100) 70 (300) 70 (500) 77 (1000)
1E16 5 (1000)
Polycrystalline W
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Where We are Going

• It is now clear that
• - Helium retention is a function of material
  and a combination of implanted dose and annealing
  temperature
• - For IFE-relevant levels of implanted helium
  and peak annealing temperatures we are near a
  limit below which helium may not accumulate
• The direction we are moving
• - More refined experiments designed to give
• a) More precise measurement of low level
  accumulation
• b) Better understanding of the kinetics
• - More detailed and experimentally coupled
  modeling.

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Neutron Depth Profiling

• 3He(n, p)T used to obtain absolute helium depth
  profile
• Used to profile monoenergetic 1.3 MeV 3He
  implanted in tungsten
• Ratio of areal densities determined by NDP agreed
  with ratio of proton yields resulting from NRA

Single crystal W implanted with monoenergetic 1.3
MeV 3He at 850C and flash-annealed at 2000C to
a dose of 1020 He/m2
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Producing IFE helium ion spectrum

• 1.6 MeV 3He degraded by 1.37 ?m C foil,
  backscattered from Au film

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Variable energy helium implantation

• 1.6 MeV 3He beam degraded by carbon foils
• Foil thickness 1.37, 2.00, 2.55, 3.55 ?m
• Approx. 10 different tilt angles (0 40) for
  each foil
• 43 degraded energy profiles weighted
  appropriately
• Implanted two single crystal samples with 1020
  He/m2 at room temp.
• One sample flash annealed to 2000C after implant
• Both samples to be analyzed by NDP

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Cavity distribution in He-implanted and annealed W
Single crystal W implanted with1019 He/m2
followed by annealing at 2000C
Single step annealing (2 sec.) resulted in the
formation of a large number of tiny cavities.
No visible cavities were observed in the 1000
step annealed (33 min.) single crystal W
Polycrystalline W implanted with1019 He/m2
followed by annealing at 2000C
The presence of grain boundaries led to
significant cavity formation and greater cavity
growth than in single crystal tungsten.
Annealing in 1000 steps resulted in no visible
cavity formation even though the NRA results
found polycrystalline tungsten had more He
retention than single crystal tungsten.
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Cavity Distribution of Helium-implanted Single
Crystal W Implanted at RT to 2 x 1017 m-2 and
annealed at 2000C for 5 sec. and repeated this
50 times for a total dose of 1 x 1019 m-2
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Thermal Desorption Spectroscopy

• Implant single crystal and polycrystalline
  tungsten with 3He
• Mass spectrometer monitors 3He partial pressure
  while sample temperature is ramped from room
  temperature to 2400C
• Goal is to determine differences in helium
  trapping/detrapping mechanisms for single crystal
  and polycrystalline tungsten under different
  implantation conditions

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730C
900C
620C
TDS data for a single crystal W sample implanted
with 5 x 1020 He/m2 at 850C. The temperature was
ramped from room temperature to 2400C at 2C/s.
Well defined desorption peaks were observed at
620, 730, and 900C. The plateau between 1000
and 1200 s occurred while the sample was held at
2400C (temperature ramp stopped due to furnace
limitations).
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Summary
At IFE relevant conditions, variables
affecting retention and eventual spalling
include - amount of helium implanted for each
fusion event 1016 ions/m2 ( IFE)
packet, 2000C has limited retention - annealing
temperature following event currently
limited to 2000C due to specimen fatigue issues
in ion beam chamber (specimen holder redesign
needed) - microstructure as expected,
helium retention at grain boundaries is an
important factor Issues - current
experiment limited in total dose and annealing
temperature - more IFE-relevant irradiations
should include shorter pulse, higher
temperature annealing (requires laser) - need to
define defect energies by
using recently developed TDS system