Novel approach to plasma facing materials 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, Lisboa, Portugal 2Associação Euratom/IST, Centro de Fusão Nuclear, Instituto Superior Técnico, Av. Rovisco Pais, Lisboa, Portugal 3Associação Euratom/IST, Departamento de Engenharia de Materiais, Instituto Superior Técnico, Av. Rovisco Pais, Lisboa, Portugal 4 National Institute of Advanced Industrial Science and Technology (AIST), Namiki, Tsukuba, Ibaraki , Japan 5NanoCarbon Research Institute, Ltd. Shinshu University, Ueda-shi Tokida , Nagano, Japan Instituto Nacional de Engenharia, Tecnologia e Inovação, I.P.

Objective Produce 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 Procedures  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 Procedures 1 Characterization of the Resulting Powders XRD Optical Microscopy Scanning Electron Microscopy Microhardness Measurements 1 Characterization of the Resulting Powders XRD Optical Microscopy Scanning Electron Microscopy Microhardness Measurements 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 Procedures Characterization of the Resulting Powders Scanning Electron Microscopy XRD Microhardness Measurments Optical Microscopy

Experimental Procedures Consolidation Milled Powders Powders were consolidated by: SPS at 800ºC Hot-Rolling at 800ºC SPS & Hot-Rolling Consolidated Material

Experimental Procedures Spark Plasma Sintering- SPS Hot-Rolling

SPS at AIST Japan Experimental Procedures

Results Processing Parameters and Microhardness of all produced batches Batch Milling Time [h] ObservationsMicrohardness [HV] W-nD-2H2 Heterogeneous powders (several kind of particles) ±282.8 W-nD-4H4 Heterogeneous powders (2 kind of particles) Homogeneous particles (bright) ±290.2 Heterogeneous and darker particles ±205.9 W-nD-4H SPS 800ºC 4 Homogeneous powders (1 kind of particles) 2796± W-nD-4H Hot-rolling 800ºC 4 Heterogeneous powders (2 kind of particles) Homogeneous particles (bright) 2780,6±553,2 Heterogeneous and darker particles 1444,0±417,7 W-nD-4H SPS and Hot-rolling 800ºC 4 Heterogeneous powders (2 kind of particles) Homogeneous particles (bright) 2706,5±282,9 Heterogeneous and darker particles 1433,1±335,5

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

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

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

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

Conclusions 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 work 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 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, Lisboa, Portugal 2Associação Euratom/IST, Centro de Fusão Nuclear, Instituto Superior Técnico, Av. Rovisco Pais, Lisboa, Portugal 3Associação Euratom/IST, Departamento de Engenharia de Materiais, Instituto Superior Técnico, Av. Rovisco Pais, Lisboa, Portugal 4 National Institute of Advanced Industrial Science and Technology (AIST), Namiki, Tsukuba, Ibaraki , Japan 5NanoCarbon Research Institute, Ltd. Shinshu University, Ueda-shi Tokida , Nagano, Japan Instituto Nacional de Engenharia, Tecnologia e Inovação, I.P.

W-nD W W-Cu Cu Plasma LAYERS

Properties W Density W = 19.3 g/cm^3 Hardness Hv W = 3.04 GPa Thermal Conductivity W = W/(m-k) nD Density nD = 3.51 g/cm^3 Micro-Hardness HV nD = GPa Thermal 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.