Mitglied der Helmholtz-Gemeinschaft Powder metallurgically produced tungsten fiber reinforced tungsten composites 15 th November 2017 | Y.Mao a , J.W.Coenen a , J.Riesch b , S.Sistla c , J.Almanstötter d , B.Jasper a , L.Raumann a , A.Litnovsky a , F.Klein a , M.Rasinski a , A.Terra a , T.Höschen b , H.Gietl b,e , M. Bram f , J. Gonzalez-Julian f , Ch.Linsmeier a and C.Broeckmann c a Institut für Energie und Klimaforschung – Plasmaphysik, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany b Max-Planck-Institut für Plasmaphysik, 85748 Garching b. München, Germany c Institut für Werkstoffanwendungen im Maschinenbau (IWM), RWTH Aachen University, 52062 Aachen, Germany d OSRAM GmbH, SP PRE PLM DMET, Mittelstetter Weg 2, 86830 Schwabmünchen, Germany e Technische Universität München, Boltzmannstrasse 15, 85748 Garching, Germany f Institut für Energie und Klimaforschung - Materials Synthesis and Processing, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
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Powder metallurgically produced tungsten fiber reinforced tungsten
A.Terraa, T.Höschenb, H.Gietlb,e, M. Bramf, J. Gonzalez-Julianf, Ch.Linsmeiera and C.Broeckmannc
a Institut für Energie und Klimaforschung – Plasmaphysik, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany b Max-Planck-Institut für Plasmaphysik, 85748 Garching b. München, Germany c Institut für Werkstoffanwendungen im Maschinenbau (IWM), RWTH Aachen University, 52062 Aachen, Germany dOSRAM GmbH, SP PRE PLM DMET, Mittelstetter Weg 2, 86830 Schwabmünchen, Germany eTechnische Universität München, Boltzmannstrasse 15, 85748 Garching, Germany f Institut für Energie und Klimaforschung - Materials Synthesis and Processing, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
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20.11.2017 Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
Tungsten in fusion reactor
Extreme conditions • High ion/neutron flux,
• high heat load (≥ 10 MW/m2)
• temperature
• thermal stresses/cycling
• …
Tungsten features unique property combination • High melting point, Tmelt = 3380 °C
• High thermal conductivity, λ = 167 W/mK,
• High temperature strength and creep resistance, • Low sputter yield, …
ITER Organization ITER Organization
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Crack formation
20.11.2017 Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
• Intrinsic brittleness of tungsten material
• Thermal heat load at the divertor: thermal
stress and thermal fatigue
G. Pintsuk et al. / Fusion Engineering and Design 88 (2013) 1858– 1861 1861
Neutron embrittlement
ITER Material Properties Handbook, ITER Document No.G74 MA 16, 2005.
A damage resilient material is required
H Bolt, et al; Journal of Nuclear Materials, Volumes 307–311, Part 1, 2002, Pages 43-52
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Fiber reinforced composites
20.11.2017 Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
Energy dissipation mechanisms:
a – pull-out of fibers
b – pull-out of matrix elements
c – crack deflection at interface
d – crack bridging by fiber
e – crack meandering at interf.
Pseudo ductile behavior
[based on Chawla 1993]
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Tungsten fiber reinforced tungsten composites
(Wf/W)
Fiber
• High strength/ductility, temperature stability
commercial, drawn tungsten wire (Osram GmbH)
Interface
• Optimum bonding, stability: e.g. oxide ceramic (Yttria)
Matrix
• Interface/fiber integrity, fiber architecture, density
Chemical vapor deposition (CVD-Wf/W)
Powder metallurgy (PM-Wf/W)
Mature industrial production route High production rate Easy to apply alloy production
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Manufacturing process and microstructure
20.11.2017 Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
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20.11.2017 Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
Raw materials
Powders:
5 µm average
particle size
Fibers:
- length: 2.4 mm
- diameter: 0.24 mm
Ductile fiber with extremely high
tensile strength up to ~3000 Mpa
1 µm
Elongated grain structure
-Zhao, Microstructure, mechanical behaviour and fracture of pure
tungsten wire after different heat treatments, 2017
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20.11.2017 Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
Process
Tungsten fiber coating with
2.5 µm Y2O3 thin film by Magnetron sputtering
Fiber and powder mixing with 30%
fiber volume fraction
PM process
Consolidation:
Field assisted sintering technology (FAST)
Hot Isostatic Pressing (HIP)
Tungsten fiber reinforced tungsten
composite
FAST
HIP
2µm
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Parameter and microstructure
Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
FAST HIP
Parameter FAST HIP
Temperature 1900°C 1600°C
Pressure 60 MPa 200 MPa
Time 4min 2h
Heating rate 200K/min 10K/min
Relative
density ~94% ~98%
7
• Dense material • Random fiber distribution • Yttria interface between fiber and matrix
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Pseudo ductile behavior of the PM produced Wf/W
20.11.2017 Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
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Pseudo ductile behavior
-pre-notched 3 point bending test
20.11.2017 Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
Qualitative measurement of the fracture behavior
Diamond wire cutting →razor blade polishing
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Pseudo ductile behavior
Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
Pure W FAST HIP
The PM produced Wf/W samples are able to show a pseudo-ductility behavior at RT. The improved resistance against
fracture relies on the energy dissipation mechanisms like fiber pull-out, crack bridging by the fibers and crack deflection.
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Carbon influence on Tungsten fiber after FAST process
20.11.2017 Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
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Brittle tungsten fiber
20.11.2017 Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
• Cleavage transgranular fracture
• Tungsten fibers after FAST process are brittle fibers
Our principle works, even with brittle fibers and matrix, the material still behave pseudo ductile. We have fiber embrittlement during the production of the composite.
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Carbon embrittlement
20.11.2017 Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
Ductile fiber Brittle fiber 1220 °C
annealing on graphite sheet
annealing on Mo bed plate
Ductile fiber Ductile fiber 1220 °C
-Marine Ilg, Diplomarbeit, 2016
• Very small amount (Dozens of ppm) of
carbon impurities will increase DBTT of
tungsten.
• “carbon embrittlement results from an
interaction between carbon atoms and
dislocations within the tungsten lattice”
Carbon content (ppm) 8 36 60
DBTT (°C) 232 368 415
-Stephens JR. Effects of interstitial impurities on the low-temperature
tensile properties of tungsten; 1964.
1900 °C
Using W foil to separate the
tungsten and the graphite
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Wf/W with ductile fiber
20.11.2017 Yiran Mao – Second Technical Meeting on Divertor Concepts, 13-16 Nov, Suzhou
