Titanium and Tantalum Used as Functional Gradient Interlayer to Join Tungsten and Eurofer97

For the DEMO reactor, tungsten is considered as an armor material. Eurofer97 is planned to be used as a structural material for the first wall and in the divertor region, especially for the shielding liner component. To date, several joining solutions between W and Eurofer97 have been developed (copper brazing, W and Eurofer97 functional gradient material (FGM), etc.). Each existing joining solution has its own advantages (joining material, improved manufacturing process). In the present study, the choice of the joining material is driven, among other constraints, by a desire to minimize the thermal stresses at the materials' interface. In this regard, FGM represents a promising solution. Another constraint that is taken into account in this study concerns the manufacturing process involved, which should be an improved industrial process. The present study proposes a joining solution, based on FGM, which, additionally to the advantages of the existing solutions, could reduce the long-term activation of the joining material. The development of a joining solution via Ti and Ta as materials constituting the FGM (Ti/Ta FGM) is presented in this paper. Due to the achieved density and the composition's accuracy, the cold spray process is shown to be adapted for the Ti/Ta FGM's manufacturing. Based on the feedback on the experience of joining between W, W/Cu FGM and CuCrZr, the final joining between W, Ti/Ta FGM and Eurofer97 is achieved using hot isostatic pressing, followed by a thermal treatment to recover Eurofer97's mechanical properties, resulting in good joining quality.