Novel approach to plasma facing materials in nuclear fusion reactors

1. Instituto Nacional de Engenharia, Tecnologia e Inovação, I.P. 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 Novel approach to plasma facing materials in nuclear fusion reactors

2. 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 W? • Highest melting point; • Highest resistance to irradiation (doesn’t contaminate the plasma); • High corrosion resistance; • Doesn’t produce armful radioactive elements Why Nanostructure?Nanoparticles act as effective sink for radiation defects. W-nD nanocomposite is a good option! Why nD? • High thermal condutivity; • Very hard material Challenge: Avoid the carbide formation!

3. Planetary Ball Mill Experimental Procedures Mechanical Alloying Inside the Container Container & Balls • 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.

4. Mechanical Alloying: 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 XRD XRD Characterization of the Resulting Powders Characterization of the Resulting Powders Scanning Electron Microscopy Scanning Electron Microscopy Optical Microscopy Optical Microscopy 1 1 Microhardness Measurements Microhardness Measurements Experimental Procedures Used Powders: • Pure elemental W (99.95% purity; median particle size 1 m) • nD particles; (agglomerates that have diameters of 2-3 m)

5. XRD Characterization of the Resulting Powders Scanning Electron Microscopy Microhardness Measurments Optical Microscopy Experimental Procedures

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

7. Experimental Procedures Spark Plasma Sintering- SPS Hot-Rolling

8. Experimental Procedures SPS at AIST Japan

9. Results Processing Parameters and Microhardness of all produced batches

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

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

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

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

14. 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.

15. 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

16. Instituto Nacional de Engenharia, Tecnologia e Inovação, I.P. 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 Novel approach to plasma facing materials in nuclear fusion reactors

17. Plasma W W-nD LAYERS W-Cu Cu

18. Properties W Density W = 19.3 g/cm^3 Hardness Hv W = 3.04 GPa Thermal Conductivity W = 163.3 W/(m-k) nD Density nD = 3.51 g/cm^3 Micro-Hardness HV nD = 88 -147 GPa Thermal Conductivity nD = 2000 W/(m-k)

19. 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.