Mechanical and microstructural characterization of HIP joints of a simplified prototype of the ITER NHF First Wall Panel

The blanket of ITER protects the vacuum vessel from neutrons and other energetic particles produced in the fusion plasma. Each of the 215 Normal Heat Flux (NHF) panels of the blanket consists of a shield block and a First Wall (FW) panel. The NHF FW panels are a complex bimetallic structure of AISI 316L(N) stainless steel (SS) backing plate and a copper alloy (CuCrZr) heat sink, covered with beryllium armor tiles. Joining of these materials is done by solid state diffusion bonding. Under the framework of a R&D roadmap parallel to the manufacturing of a full-scale prototype of a FW panel of ITER, this work describes studies on the microstructure and strength of CuCrZr/SS and CuCrZr/CuCrZr joints of a simplified 10-fingers prototype of a FW panel manufactured by Hot Isostatic Pressing (HIP). Results on mechanical tests performed following ITER recommendations are compared to F4E specifications. Microstructural characterization of the interface was performed. Thermal history of the component is correlated with the mechanical behavior of the interfaces. Results show that appropriate parameters of the solution annealing after HIP and of the CuCrZr ageing during final HIP diffusion bonding are essential to achieve the specified strength of the joints.