Fabrication of DEMO divertor target mock-up by HRP technology with tungsten fiber reinforced tungsten as armour material

The current consolidated process for the fabrication of a target divertor for ITER foresees armour material monoblocks with Oxygen Free Electronic Grade copper (OFE-Cu, Cu) interlayer joined to CuCrZr ITER Grade (CuCrZr-IG) cooling pipes by diffusion bonding. ENEA's Special Technologies Laboratory (TES) developed the Hot Radial Pressing (HRP) technology which is the diffusion bonding technique eligible for the European DEMOnstration fusion power plant (EU-DEMO) divertor target. Tungsten (W) is also the primary armour material candidate for the EU-DEMO divertor target. However, during operation at high temperature the intrinsic brittleness of W below the Ductile-to-Brittle-Transition-Temperature can generate fractures inside the plasma facing components. Alternative armour materials able to mitigate the intrinsic drawbacks of pure W are being investigated in the context of the EUROfusion workpackage Materials (WPMAT). Among the many alternatives, tungsten fiber-reinforced tungsten (Wf/W) has showed an excellent improvement of the fracture toughness. In this work, a mock-up using Wf/W ITER-like monoblocks was fabricated. The Cu interlayer was made by casting. Once machined, the advanced Wf/W-Cu monoblocks were joined by HRP to the CuCrZr cooling tube. The fabrication of the mock-ups required an optimization of process parameters within the range in which the thermo-mechanical properties of the copper interlayer and the Wf/W-Cu armour blocks are not yet degraded. Non-destructive examination (NDE) by ultrasonic inspection were performed on the advanced Wf/W monoblocks before mock-up fabrication, after OFE-Cu casting on the Wf/W-Cu blocks and after HRP joining of the blocks with the CuCrZr pipe.