Development of Functional Scales for Joining of Divertor Components Based on Electrochemical Plating Technology

In fusion technology, functional scales are required for various application fields like first wall tungsten coating, anti-corrosion or tritium permeation barriers, and brazing layers in joining technology. Established processes for layer deposition exhibit several kinds of drawbacks ranging from difficulty controlling layer thickness, inhomogeneity of coatings, application limits because of geometrical reasons, or critical thermal loading. Inherently, electrochemical plating technology does not exhibit these critical features. Growing of galvanic layers depends on the transported charge and thus can easily be controlled by current flow and/or deposition time. The main part of this development work was focused on voltammetric analyses to assist the deposition of transition metals on refractory metal surfaces, e.g., tungsten and Eurofer steel, and to deliver boundary conditions for electrolytes. Typical elements that can be used in joining may range from Ti, V by Ni, Fe up to Pd, and Cu. However, a direct joining of tungsten onto Eurofer steel by copper is metallurgically impossible due to missing miscibility of copper with tungsten. Thus, interlayers with an active functionality are required, which interact with both bulk components and filler to obtain a sound braze joint brazing. For both W-W and W-Eurofer joints, demonstrators were successfully fabricated and analyzed by metallurgical and physical methods.