Novel approach to plasma facing Novel approach to plasma facing materials in nuclear fusion reactorsmaterials in nuclear fusion reactors

V. Livramento1, J.B. Correia1, D. Nunes3, P.A. Carvalho3, H. Fernandes2,

C. Silva2, K. Hanada4, N. Shohoji1, E.Osawa5

1INETI, Departamento de Materiais e Tecnologias de Produção, Estrada do Paço do Lumiar, 1649-038 Lisboa, Portugal

2Associação Euratom/IST, Centro de Fusão Nuclear, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal

3Associação Euratom/IST, Departamento de Engenharia de Materiais, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal

4 National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan

5NanoCarbon Research Institute, Ltd. Shinshu University, 386-8567 Ueda-shi Tokida 3-15-1, Nagano, Japan

Instituto Nacional de Engenharia, Tecnologia e Inovação, I.P.

ObjectiveObjectiveProduce a W-nDiamond composite, using High Energy milling of powders and consolidation in order to develop a suitable material for the first wall of nuclear fusion reactors.

Why Nanostructure? Nanoparticles act as effective

sink for radiation defects.

Why W?• Highest melting point;• Highest resistance to irradiation (doesn’t contaminate the plasma);• High corrosion resistance;• Doesn’t produce armful radioactive elements

Why nD?• High thermal condutivity;• Very hard material

Challenge: Avoid the carbide formation!

W-nD nanocomposite is

a good option!

Mechanical Alloying

Experimental Experimental ProceduresProcedures

Processing of elemental powders in high energy ball mills;Dynamic balance between cold welding and fracture gradual mixture; Nanostructure in the end;Especially suited for the production of composite materials.

Inside the Container

Container & Balls

Planetary Ball Mill

Experimental Experimental ProceduresProcedures

Used Powders:• Pure elemental W (99.95% purity; median particle size 1 m)• nD particles; (agglomerates that have diameters of 2-3 m)

WC balls with 10 mm of diameter

250 ml WC containers

The container was first evacuated and then filled with Argon

Retsch PM 400 Planetary Ball Mill

Rotation speed = 200 rpm

Mechanical Alloying:

Experimental Experimental ProceduresProcedures

Characterization of the Resulting

Powders

Scanning Electron

Microscopy

XRD

Microhardness Measurments

Optical Microscopy

Experimental Experimental ProceduresProcedures

Consolidation

Milled Powders

Powders were consolidated by:

• SPS at 800ºC

• Hot-Rolling at 800ºC

• SPS & Hot-Rolling

Consolidated

Material

Experimental Experimental ProceduresProcedures

Spark Plasma Sintering- SPS

Hot-Rolling

SPS at AIST Japan

Experimental Experimental ProceduresProcedures

ResultsResultsProcessing Parameters and Microhardness of all produced batches

BatchMilling Time

[h]Observations Microhardness [HV]

W-nD-2H 2Heterogeneous

powders (several kind of particles)

1558.0±282.8

W-nD-4H 4Heterogeneous

powders (2 kind of particles)

Homogeneous particles (bright) 2427.5±290.2

Heterogeneous and darker particles 1461.0±205.9

W-nD-4HSPS 800ºC

4Homogeneous

powders (1 kind of particles)

2796±271.2.6

W-nD-4HHot-rolling 800ºC

4Heterogeneous

powders (2 kind of particles)

Homogeneous particles (bright) 2780,6±553,2

Heterogeneous and darker particles 1444,0±417,7

W-nD-4HSPS and Hot-rolling

800ºC4

Heterogeneous powders (2 kind of

particles)

Homogeneous particles (bright)2706,5±282,9

Heterogeneous and darker particles1433,1±335,5

ResultsResultsXRD patterns for W+nD powders milled for 2 and 4 hours and consolidated samples:

1

1,5

2

2,5

3

3,5

4

4,5

5

5,5

20 40 60 80 100 120 140 1602 q

W WC W2C WO2 Diam.

W-nD - 2H - 200rpm

W-nD - 4H - 200rpm

W-nD - 4H - 200rpm Lam. 800ºC

W-nD - 4H - 200rpm roll. 800ºC new

W-nD - 4H - 200rpm SPS 800ºC

W-nD - 4H - 200rpm Roll + SPS 800ºC

ResultsResults

SEM/BSE pictures of W+nD powders milled for 2 h and 4h respectively (200rmp):

ResultsResults

SEM/BSE image of W+nD subjected to MA (4 h at 200 rpm) and rolling at 800ºC and respectively EDS chemical analysis:

ResultsResultsW-nD subjected to MA (4 h at 200 rpm) and rolling at 800ºC and exposed to the edge plasma:

ConclusionsConclusions

It is possible to performe MA of W and nD powders at room temperature without agglomeration Short milling time of only 2 and 4 hours provides a favourable condition for the least contamination of ball material in the mechanical alloying.High-energy milling at 200 rpm followed by SPS at 800ºC represents the best combination of processing parameters for obtaining dense W-nD nanocomposite. Bulk specimens were obtained without significant carbide formation.Exposure to plasma of rolled W-nD produced surface modification of structure. However, below 1 mm the W-nD nanocomposite was essentially preserved.

Perspectives of Future Perspectives of Future workwork

Optimize the consolidation parameteres for W-nDiamond

Thermal conductivity tests on the way

More exposure experiments at ISTTOK and at FTU of the Consolidated materials

Novel approach to plasma facing materials in Novel approach to plasma facing materials in nuclear fusion reactorsnuclear fusion reactors

V. Livramento1, J.B. Correia1, D. Nunes3, P.A. Carvalho3, H. Fernandes2,

C. Silva2, K. Hanada4, N. Shohoji1, E.Osawa5

1INETI, Departamento de Materiais e Tecnologias de Produção, Estrada do Paço do Lumiar, 1649-038 Lisboa, Portugal

2Associação Euratom/IST, Centro de Fusão Nuclear, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal

3Associação Euratom/IST, Departamento de Engenharia de Materiais, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal

4 National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan

5NanoCarbon Research Institute, Ltd. Shinshu University, 386-8567 Ueda-shi Tokida 3-15-1, Nagano, Japan

Instituto Nacional de Engenharia, Tecnologia e Inovação, I.P.

W-nD

W

W-Cu

Cu

Plasma

LAYERS

PropertiesProperties

W

Density W = 19.3 g/cm^3

Hardness Hv W = 3.04 GPa

Thermal Conductivity W = 163.3 W/(m-k)

nDDensity nD = 3.51 g/cm^3Micro-Hardness HV nD = 88 -147 GPaThermal Conductivity nD = 2000 W/(m-k)

SPS- The pulsed DC passes through the graphite die and the compacted powders;- The heat is generated internally, that provides a very high rates of heating and cooling;- This process has the potential of densifying the powders with nanosize or nanostructure avoiding the coarsening which normally accompanies the normal densification routes.

Hot-Rolling- Metallurgical process, where the material is passed, deformed between rolls, applying a controlled load;- permits large deformation of the material with a low number of rolling cycles;- Do not affect microstructural properties;- It’s possible to obtaine material with a certain specification or size.