Chemical vapor deposition and infiltration for the production of tungsten fiber reinforced tungsten composite material

Contribution submission to the conference Regensburg 2016Chemical vapor deposition and infiltration for the productionof tungsten fiber reinforced tungsten composite material —∙Martin Aumann1, Jan Willem Coenen1, Hanns Gietl2, TillHoeschen2, Johann Riesch2, Klaus Schmid2, Rudolf Neu2, andChristian Linsmeier1 — 1Forschungszentrum Juelich GmbH, Institutfür Energie- und Klimaforschung, 52425 Juelich — 2Max-Planck-Institut für Plasmaphysik, 85748 GarchingDue to its high melting point, high corrosion resistance and its preferableproperties in terms of hydrogen retention, tungsten is a promisingcandidate in future nuclear fusion devices. However, the mechanicalbehavior of tungsten is crucial, as it is inherently brittle at room temperature.As possibility to overcome this brittleness, a composite materialcan be formed, which shows pseudo-ductility and therefore avoidscatastrophic failure of the material. A possibility to produce such aWf/W-composite is chemical vapor deposition and chemical vapor infiltration,where tungsten is deposited on small tungsten wires throughthe reaction of WF6 and H2. With ongoing infiltration time, pores areformed between the fibers, which decrease in size through the chemicalreaction. For better process understanding, a pore model was established,which solves the mass balance inside the pore and the resultingpore diameter simultaneously. It shows a significant difference in diameterfor longer infiltration times. This behavior shall be proved inexperiments with an experimental pore, which is similar to the simulatedone. Furthermore also kinetic investigations on the chemicalsurface reaction are carried out to increase the process understanding.Part: MMType: Vortrag;TalkTopic: Transport (Diffusion, Leitfähigkeit,Wärme)/ Transport (Diffusion,conductivity, heat)Email: [email protected]

Tungsten fibre-reinforced composites for advanced plasma facing components

AbstractThe European Fusion Roadmap foresees water cooled plasma facing components in a first DEMO design in order to provide enough margin for the cooling capacity and to only moderately extrapolate the technology which was developed and tested for ITER. In order to make best use of the water cooling concept copper (Cu) and copper-chromium-zirconium alloy (CuCrZr) are envisaged as heat sink whereas as armour tungsten (W) based materials will be used. Combining both materials in a high heat flux component asks for an increase of their operational range towards higher temperature in case of Cu/CuCrZr and lower temperatures for W. A remedy for both issues- brittleness of W and degrading strength of CuCrZr- could be the use of W fibres (Wf) in W and Cu based composites. Fibre preforms could be manufactured with industrially viable textile techniques. Flat textiles with a combination of 150/70 µm W wires have been chosen for layered deposition of tungsten-fibre reinforced tungsten (Wf/W) samples and tubular multi-layered braidings with W wire thickness of 50 µm were produced as a preform for tungsten-fibre reinforced copper (Wf /Cu) tubes. Cu melt infiltration was performed together with an industrial partner resulting in sample tubes without any blowholes. Property estimation by mean field homogenisation predicts strongly enhanced strength of the Wf/CuCrZr composite compared to its pure CuCrZr counterpart. Wf /W composites show very high toughness and damage tolerance even at room temperature. Cyclic load tests reveal that the extrinsic toughening mechanisms counteracting the crack growth are active and stable. FEM simulations of the Wf/W composite suggest that the influence of fibre debonding, which is an integral part of the toughening mechanisms, and reduced thermal conductivity of the fibre due to the necessary interlayers do not strongly influence the thermal properties of future components