Al-based Barrier Development for Nuclear Fusion Applications

Ferritic-martensitic steels of the 8-10 wt.-% Cr type are considered for applications in nuclear technology as structural materials of blanket components in future fusion and also Gen IV-type lead-cooled fast reactors. Due to operational conditions in e.g. fusion reactors, the structural materials will be in contact with heavy liquid metals (HLMs) and their corrosion behavior is of significance for their successful long-term performance. The specific physical chemistry of HLMs, e.g. like Pb-15.7Li for fusion systems, dissolution corrosion is a major corrosion mechanism of iron-based alloys. If no oxide layer formation on steel surfaces can thermodynamically occur, coatings are the solely solution to minimize corrosion effects at higher operational temperatures.
Fe-Al layers with alumina on top have revealed that they can fulfill a distinct reduction of corrosion rate. Two electrochemical-based processes for deposition of Al scales were successfully developed at Forschungszentrum Karlsruhe. The first process (ECA) is based on an organic electrolyte and the second one (ECX) consists of metal salts dissolved in an ionic liquid. Coatings in the µm‑range can be deposited with exact controllable thicknesses. In this paper the formation of protective scales will be shown in dependence of relevant process parameters, illustrated by metallurgical investigations and SEM/EDX analyses.