Tungsten fiber reinforced tungsten (Wf / W) produced by CVD and CVI

Due to excellent thermal and hydrogen retention properties, tungsten is the main candidate for first wall and divertor materials in future fusion reactors. However, the intrinsic brittleness of tungsten is a concern regarding high transient heat loads and neutron irradiation in the fusion environment. To overcome this drawback, tungsten fiber reinforced tungsten (Wf/W) composites are being developed relying on an extrinsic toughening principle. One processing route is the chemical vapor deposition and infiltration of tungsten fiber fabrics. The major challenge for this route is to prevent voids within the composite, which can easily occur if the tungsten film growth separates not yet infiltrated domains from gas flow supply. To achieve fully dense materials the underlying principles have to be fully understood. To asses this process parameters are varied in simplified experimental set-ups to bring a simulation model in line with the experimental data. The model is taking into account the kinetics for adsorption of the reactants, surface reactions, film growth and desorption of the side products. All are influenced by temperature, pressure, gas mixing ratio and gas flow velocity as well as the substrate geometry and related transport mechanisms. First experimental and theoretical results will be presented.