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Max-Planck-Institut fr Plasmaphysik Contributions of tungsten-fibre reinforced tungsten composites to divertor concepts of future fusion reactors J. Riesch a , R. Neu a,b , J. Almansttter c , M. Aumann d , J.W. Coenen d , H. Gietl a , T.

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SLIDE 1

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 1

Max-Planck-Institut für Plasmaphysik

  • J. Riescha, R. Neua,b, J. Almanstötterc, M. Aumannd, J.W. Coenend, H. Gietla,
  • T. Höschena, G. Holznera, M. Lia, Ch. Linsmeierd, J.-H. Youa

a Max-Planck-Institut für Plasmaphysik, D-85748 Garching, Germany b Fakultät für Maschinenbau, Technische Universität München, D-85748 Garching, Germany c OSRAM GmbH, Corporate Technology CT TSS MTS MET, Mittelstetter Weg 2, 86830 Schwabmünchen, Germany d Forschungszentrum Jülich GmbH, IEK - Plasmaphysik, D-52425 Jülich, Germany

Contributions of tungsten-fibre reinforced tungsten composites to divertor concepts of future fusion reactors

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SLIDE 2

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 2

Tungsten as Plasma-Facing Material

J.W. Coenen PFMC 2015

W properties

(relative scale)

motivation for W from PWI

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SLIDE 3

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 3

Content

  • Wf / W materials state of the art and development

– K-Doped W wires – As-fabricated state – Embrittled state

  • Aspects for future divertor concepts

– Toughening – Temperature window – PWI

  • Summary
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SLIDE 4

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 4

Wf/W – state of the art

[based on Chawla 1993]

  • Theory
  • Synthesis

– Wound fibre preform (drawn W wire) + CVI (dual step)  Model system + small bulk samples (2.5x3x25 mm)

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SLIDE 5

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 5

  • Manufacturing technique identified + first

samples

  • Enhanced toughness at room temperature –

shown for bulk samples

  • Toughness mechanisms after embrittlement –

shown for model systems  Proof-of-principle – TRL 2  Ranked as risk mitigation PFC/HHF material in EU Fusion roadmap towards DEMO

Wf/W – state of the art: summary

Technology Readiness Level (TRL)

Basic Technology Research System Test, Launch & Operation DEMO range

[Stork 2013]

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SLIDE 6

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 6

Wf / W – Materials Development

Matrix Fibre: drawn W-wire Interface

Address all constituents + all aspects of synthesis

  • Fibre studies

 Strength: influence of diameter  Thermal stability

  • Interface studies

 Thermal stability  Optimisation of adhesion  Activation behaviour

  • Matrix synthesis

 Optimisation: layered CVD / CVI  Alternatives: powder metallurgical Wf / W

  • Composite studies

 Investigate mechanical properties  Understand embrittlement issues embrittlement by overheating embrittelment by neutron irradiation

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SLIDE 7

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 7

Thermal Stability of K-Doped W wires

Temp [K] As-fabricated 1273 1573 1873 2173 2573

≈ 2400 K: abnormal grain growth2)

2) [Pink et al. 1989]

2573 K Extensive grain growth 2173 K As-produced

50 µm

Single fibre tension tests on as-fabricated and annealed samples

  • W doped with 60-75 ppm K (producer: OSRAM GmbH)
  • Diameter: 150 µm, Fiber Length: 80 mm
  • Annealing time: 30 min
  • Annealing temperatures
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SLIDE 8

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 8

Tensile strength of pure W: ≈ 2900 MPa Ta [K] As-produced 1273 1573 1873 2173 2573

σu [MPa] 2745±16 2409±16 2221±12 2089±11 1968±9 1274±105 εf [10-2] 3.0±0.2 2.6±0.2 3.0±0.4 2.7±0.1 3.4±0.5 << 1.0

Stress-Strain curve of as produced and heat-treated fiber

Thermal Stability of K-Doped W wires

Tensile Tests of 150 µm W wires

  • J. Riesch, PFMC 2015
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SLIDE 9

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 9

Tensile strength of pure W: ≈ 2900 MPa

Stress-Strain curve of as produced and heat-treated fiber

Ta [K] As-produced 1273 1573 1873 2173 2573

σu [MPa] 2745±16 2409±16 2221±12 2089±11 1968±9 1274±105 εf [10-2] 3.0±0.2 2.6±0.2 3.0±0.4 2.7±0.1 3.4±0.5 << 1.0

Thermal Stability of K-Doped W wires

Tensile Tests of 150 µm W wires

  • J. Riesch, PFMC 2015
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SLIDE 10

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 10

Brittle Tensile strength of pure W: ≈ 2900 MPa

Stress-Strain curve of as produced and heat-treated fiber

Ta [K] As-produced 1273 1573 1873 2173 2573

σu [MPa] 2745±16 2409±16 2221±12 2089±11 1968±9 1274±105 εf [10-2] 3.0±0.2 2.6±0.2 3.0±0.4 2.7±0.1 3.4±0.5 << 1.0

Thermal Stability of K-Doped W wires

Embrittlement of pure W

No embrittlement below 2200 K

Tensile Tests of 150 µm W wires

  • J. Riesch, PFMC 2015
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SLIDE 11

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 11

Production of multi-fibre samples by CVI & CVD

Wf /W Composite Studies

  • 10 Layers a 220 fibres (pure), fibre volume fraction ≈ 0.3, unidirectional
  • 62 x 57 x 3.5-4 mm3, 194 g
  • 93 – 98 % depending on location, 94.2 % overall density (Archimedes)
  • Er2O3 interface

First bulk Wf / W for extended testing CVD and layered deposition

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SLIDE 12

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 12

Artificial notch First fibre layer half cut

Mechanical Properties of Wf / W

Ductile Fibre (pure) Strength 2900 MPa, Fracture strain 2% Brittle Fibre (pure) Strength 900 MPa, Fracture Strain 0,2 %

  • Multi-fibre composite

 W-CVD layered deposition  Polished  2.2 mm x 3 mm

  • As fabricated and

Embrittled (2000 K, 30 min) Wf / W

2 mm

  • Stepwise 3-point bending +

In-situ surface observation in electron microscope (ESI)

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SLIDE 13

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 13

theory (lit.) Multi-fibre sample

Mechanical Properties of Wf / W

Load Displacement failure brittle material

Controlled crack propagation + rising load bearing capacity  ‘Ideal’ behaviour of composite Bending test of as fabricated Wf /W composites

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SLIDE 14

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 14

Theory Embrittled fibre

Controlled crack propagation + rising load bearing capacity  Toughening works also after embrittlement

matrix failure = bulk material failure

Mechanical Properties of Wf / W

bending test of embrittled Wf/W composites

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SLIDE 15

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 15

Aspects for future divertor concepts

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SLIDE 16

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 16

Operation temperature window

Based on Zinkle et.al 2000 [S.J. Zinkle et al., FED 51-52 (2000) 55-71] and Timmis (CuCrZr) [Timmis, Material Assessment Report on the Use of Copper Alloys in DEMO (2012)]

Ductile fibre & bridging/pull-out if embrittled Potassium doped fibre Recrystallisation Inherent brittleness & radiation embrittlement

  • Fibre tests at elevated temperature
  • Fibre tests after neutron irradiation
  • Tension tests on recrystallised Wf/W
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SLIDE 17

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 17

Cracking of tungsten

[M. Wirtz et al., FED 88 (2013) 1768-1772] [M. Wirtz et al., Phys. Scr. T145 (2011) 014058]

Deep cracking of divertor elements

Electron beam (FE200, France), 10-20 MW/m2 up to 1000 cycles, actively cooled

Result of low cycle fatigue (crack initiation) and brittle behavior during cool down

[Pintsuk et al., Fusion Eng Des 88 (2013) 1858– 1861]

Incoperate Wf/W

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SLIDE 18

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 18

No bonds 1 bonds 3 bonds

No tensile stress concentration at crack tip

1/3 surface bond*

* The surfaces from depth 1.0 to 1.5 mm and from 2.0 to 2.5 mm are bonded.

Stresses (MPa) in x- direction at the mid- surface J-integrals for a pre-crack of 3 mm

0,5 1 1,5 2 2,5 3 3,5 no bond 1 bond 3 bonds 1/3 surface bond J-integral mJ/mm2 mid critical

First results of impact of bridging on J-integrals

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SLIDE 19

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 19

Plasma wall interaction

Matrix Fibre: drawn W-wire Interface

Tungsten fibre-reinforced tungsten

  • Special microstructure

 Fibre, Matrix

  • New materials
  • Interfaces, Doped W wire
  • Complicated structures
  • Internal Interfaces, different microstructures

 Many aspects to be considered if used as plasma facing material e.g.

  • Thermal stability
  • Activation
  • Interaction with hydrogen
  • Erosion
  • …
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SLIDE 20

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 20

K doped W wire: activation

18 ppm K

K doping of wire: no increase of activation

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SLIDE 21

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 21

Summary & Outlook

Wf / W materials development

  • K-Doped W wires show high strength and ductility up to annealing temperatures
  • f 2200 K
  • Very high toughness at room temperature due to ductility of fibres
  • Toughness after high temperature embrittlement

Wf / W prospects for future fusion reactors

  • Enhancement of temperature window
  • Solution for cracking problem
  • Complex PWI issues

Next steps

  • Fibre tests at elevated temperature
  • Optimisation of manufacturing process
  • WILMA
  • PM studies
  • PWI studies on constituents and model systems
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SLIDE 22

1st IAEA Divertor Concepts, Sept. 29 – Oct. 2nd, 2015, Wien R.Neu 22

Thank you for your attention