Development of a robust Be/F82H diffusion bond for ITER TBM

R.M. Hunt

Fusion Nuclear Science & Technology Annual MeetingAugust 2, 2010

EngineeringIntroduction• 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

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Armor coating on plasma facing surfaces

EngineeringBackgroundImportant 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

EngineeringMethod for Achieving Robust Heterogeneous Joints

• 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

EngineeringInitial Experiments

• 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

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5 cm

Tita

nium

Copp

er

RAFM SteelBeryllium

Engineering

100 μme

Strength of Cu/RAFM interface

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

F82H F82H

CuCu

Tensile behavior of HIPed Cu/F82H

Fractured surface – HIPed @ 700 C Cross-sec – HIPed @ 850 C

10 μme

EngineeringSupport during Experiment

• 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

EngineeringFabrication of Full Be/RAFM Joint

• 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

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Interlayer 1 Interlayer 2Test 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

Engineering1st Round of Samples• Samples debonded after attempt to wire cut• No mechanical tests could be performed

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EngineeringFailure Mechanism Investigation

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Auger #2Auger #1

Auger #3 & #4

Auger #5

Bond: 700 C, 10µm Ti Bond: 750 C, 20µm Ti

Auger Electron Spectroscopy (AES) and Energy Dispersive Spectroscopy (EDS) used to characterize compositon

EDS #1

EDS #2

Engineering

Backscatter SEM + EDS(performed at UCSD Pisces Lab)

TitaniumCopper

ChromiumIron

TitaniumCopper

ChromiumIron

HIP @ 700 °C -- 10µm Ti + 20µm Cu HIP @ 750 °C -- 20µm Ti + 20µm Cu

EngineeringCurrent WorkInvestigation 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

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EngineeringReferences

1. T. Hirose, M. Ando, H. Ogiwara , H. Tanigawa, M. Enoeda, M. Akiba, Fus. Eng. Design, doi: 10.1016/j.fusengdes.2010.06.002.

2. D.W. White Jr. and J.E. Burke, The Metal Beryllium, The American Society for Metals, 1955.3. ITER. ITER Structural Design Criteria for In-vessel Components. G 74 MA 8 01-05-28 W0.2.4. P. Sherlock, A. Erskine, P. Lorenzetto, A.T. Peacock, Fus. Eng. Design, 66 (2003) 425.5. N. Baluc, DS Gelles, S. Jitsukawa, A. Kimura, RL Klueh, GR Odette, B. Van der Schaaf, and J.

Yu. Status of reduced activation ferritic/martensitic steel development. Journal of Nuclear Materials, 367:33{ 41, 2007. 61

6. S. Kundu, M. Ghosh, A. Laik, K. Bhanumurthy, GB Kale, and S. Chatterjee. Diffusion bonding of commercially pure titanium to 304 stainless steel using copper interlayer. Materials Science & Engineering A, 407(1-2):154{160, 2005.

7. J.S. Lee, J.Y. Park, B.K. Choi, D.W. Lee, B.G. Hong, and Y.H. Jeong. Beryllium/ferritic martensitic steel joining for the fabrication of the ITER test blanket module rst wall. Fusion Engineering and Design, 84(7-11):1170{1173, 2009.

8. Jeong-Yong Park, Yang-Il Jung, Byung-Kwon Choi, and Yong-Hwan Jeong. Current status of R&D in fabrication technology of plasma facing components for ITER rst wall and TBM. Korea Atomic Energy Research Institute, September 2009.