Brazing alloys characterization for EU-DEMO Divertor Target

In the framework of the roadmap of the DEMO reactor design pursued by the EUROfusion Programme, R&D activities have been promoted for the technological development of Plasma Facing Components (PFCs). Dedicated research activity has been undertaken at ENEA to support the development of technological solutions for the monoblock-pipe joining in order to reduce the use of materials having high activation and/or a degradation under neutron irradiation. For this purpose, a preliminary brazing alloy screening was carried out: a total of seven brazing alloys were identified and tested (i.e. Gemco, Nicuman23, TiCuNi, CuTiZrNi and three alloys with different percentages of Cu and Ge). For each brazing alloy, a wettability test on joint base materials (i.e., W and Cu) was performed. Then, three samples were fabricated joining tungsten monoblocks, without Cu interlayer, on a W fiber-reinforced Cu composite cooling pipe; other three samples were realized joining W monoblocks, with and without Cu interlayer on standard ITER-grade CuCrZr pipes. Non-destructive Ultrasonic Testing (UT) examinations were performed on each sample and showed that the monoblocks surface was not fully attached to Wf-Cu pipes; as regard the samples with CuCrZr pipes, excellent results have been achieved both in the case with and without Cu interlayer. From the results, Gemco seems to be the most promising commercial alloy among the tested ones, thanks to its low amount of Nickel and the good joining capabilities.