Development of a robust Be/F82H diffusion
bond for ITER TBM
R.M. Hunt
Fusion Nuclear Science & Technology Annual Meeting
August 2, 2010
Introduction
Engineering
• Application: Development of TBM technologies vital for
future fusion demonstration reactors
– Breeder blanket structural material
 Reduced activation ferritic/martensitic (RAFM) steel
– Plasma facing armor material
 Beryllium is one primary candidate
• Prospective Joining Process: Hot Isostatic Pressing (HIP)
• Scope of Research:
– Create methodology for development of a robust diffusion
bond between beryllium and RAFM steel
– Characterize the strength of the developed bond
– Simulate cyclic thermal loading in FEM to determine min.
strength criteria
• Plastic relaxation of interface from differential thermal
expansion
• Crack initiation and growth at interface edges
Armor coating on
plasma facing
surfaces
2/12
Background
Engineering
Important bonding considerations:
• Formation of brittle intermetallic layers
–
–
–
–
•
Be is highly reactive w/ most of the elements in the periodic table
These often have much less desirable mechanical properties than parent materials
Formation is not easily predictable
Bond strength appears to be inversely proportional to width of certain reaction layers [1]
Excessive heat treatment of the bonded materials
– Beryllium shows grain coarsening above roughly 850 °C [2]
– Post weld heat treatments for F82H occur at 750 °C [1]
•
Incomplete coalescence of surfaces if temperature is not sufficiently high
 Narrow window for bonding conditions
Importance of high strength bond:
• High heat flux creates stress from differential thermal expansion of dissimilar
materials
• Cyclic high heat pulses from plasma cause fatigue in joint
Method for Achieving Robust Heterogeneous Joints
Engineering
• Insert diffusion barrier
– to prevent formation of deleterious BeCu & BeFe intermetallics
– Limited material options. Ti used with good results in ITER FW
application
– Ti diffuses well into both Be and Cu [4]
• Insert compliancy layer (pure Cu)
– to reduce stress from differential thermal expansion [5]
– And to prevent formation of FeTi [6]
• Recent work in Japan [2] and Korea [7,8] on Be//FMS bond
– Used Cr/Cu and Ti/Cu layer combinations with promising results
Copper
Beryllium
Titanium
Initial Experiments
Engineering
RAFM Steel
• Prior to inclusion of Beryllium
– Anneal Ti/Cu coupons
• To measure penetration depth of Ti
in Cu and Cu in Ti
– Fabricate Cu/RAFM HIP coupons
• Test strength of Cu/RAFM interface
• Determine optimum HIP conditions
5 cm
5/12
Strength of Cu/RAFM interface
Tensile behavior of HIPed
Cu/F82H
Engineering
Sample processed at:
• 650 ° C
– Failed w/o plasticity at 134
MPa
– Fractured surface revealed
polishing markings
• 700 ° C
– Failed at UTS of Cu (210 MPa),
though still at interface
– Surface shows some
attachment of Cu
• 750, 800, 850 °C
– Ductile failure in Cu
– Peak strength above strength
of parent Cu
Fractured surface – HIPed @ 700 C
Cross-sec – HIPed @ 850 C
F82H
F82H
Cu
Cu
100 μm
e
10 μm
e
Support during Experiment
Engineering
• Received support from vendors/labs across the country:
– F82H donated by JAEA (F82H), Beryllium S65 by Brush-Wellman
(Elmore, OH)
– Cans machined at UCLA MAE shop
– Deposition of thin film at Thin Film Technology (Buellton, CA)
– Surface prep at SNL-Livermore (Livermore, CA)
– E-beam weld closure of cans at Electrofusion Products (Fremont, CA)
– HIP cycles by Bodycote (Andover, MA)
– Test specimen EDM cut by Axsys Technologies Inc. (Cullman, AL)
– Mechanical tests and AES provided by SNL-Livermore
– Toughness tests performed at UCSB Materials Eng. Dept.
– SEM + EDS/WDS analysis at UCSD Pisces Lab
Fabrication of Full Be/RAFM Joint
Engineering
•
Utilized results from Ti/Cu and Cu/RAFM interfacial studies to narrow
conditions
•
First 4 samples
– varied HIP temperature and diffusion barrier thickness
– additional rounds to follow
Interlayer 1
Interlayer 2
Test No.
HIP Temp.
Material
Thickness
Material
Thickness
#1
700 °C
Ti
10 μm
Cu
20 μm
#2
700 °C
Ti
20 μm
Cu
20 μm
#3
750 °C
Ti
10 μm
Cu
20 μm
#4
750 °C
Ti
20 μm
Cu
20 μm
#5-(10)
TBD
TBD
TBD
TBD
TBD
8/12
1st Round of Samples
Engineering
• Samples debonded after attempt to wire cut
• No mechanical tests could be performed
9/12
Failure Mechanism Investigation
Engineering
Auger Electron Spectroscopy (AES) and
Energy Dispersive Spectroscopy (EDS) used to characterize compositon
Auger #3 & #4
Auger #2
Auger #1
EDS #1
EDS #2
Auger #5
Bond: 700 C, 10µm Ti
Bond: 750 C, 20µm Ti
10/12
Backscatter SEM + EDS
(performed at UCSD Pisces Lab)
Titanium
Copper
Chromium
Iron
HIP @ 700 °C -- 10µm Ti + 20µm Cu
Engineering
Titanium
Copper
Chromium
Iron
HIP @ 750 °C -- 20µm Ti + 20µm Cu
Current Work
Engineering
Investigation of cause for debond
• High oxygen content in Titanium deposition
• Additional EDS/WDS across unfractured samples to see Be/Ti
diffusion
FEM Work
• copper relaxation during thermal stressing
• crack initiation and growth at interface
12/12
References
1.
2.
3.
4.
5.
6.
7.
8.
Engineering
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