Speaker
Sven-Erik Wulf
(Institute for Applied Materials)
Description
Different breeding blanket designs for a future fusion power plant (DEMO) consider Eurofer steel as a main structural material. Nevertheless, RAFM steels suffer from severe corrosion attack in Pb-15.7Li, which acts as breeding material in the liquid breeder blanket designs, e.g. HCLL, WCLL and DCLL. The resulting corrosion products may cause safety risks e.g. concerning tube plugging due to possible precipitation of dissolved steel components.
Two electroplating processes were developed in the past to produce protective Al-based coatings on RAFM steels. These coatings proved that they could protect the underlying RAFM steel from corrosion in flowing Pb-15.7Li at fusion relevant conditions. In this context electroplating processes i.e. ECA and ECX, showed favorable characteristics compared to hot-dip aluminization.
Beyond an adapted heat treatment, both electrochemical processes need reliable pretreatment processes of the RAFM substrates prior to the Al-deposition, to prevent coating defects such as insufficient covering and weak adhesion. These coating failures increase the risk of defects in the corrosion barriers after the heat treatment and therefore may promote early coating breakdowns in flowing Pb-15.7Li environment. However the influence of e.g. the Eurofer substrate condition prior to the pretreatment and the duration of the pretreatment, on the coating appearance and homogeneity were not examined in detail until now.
This study examined these influences on defect formation by electrochemical measurements and SEM/BSE examinations. Besides storage time between mechanical preparation of the samples and electrodeposition, the duration of the anodic pretreatment of Eurofer samples was varied prior to the Al-plating by ECX process. It was shown that the degree of covering of aluminum on RAFM steel substrates depended on both parameters. From these findings optimized pretreatment parameters were derived that increase the reliability of the whole Al-based barrier fabrication process to achieve improved Fe-Al coatings with smooth and dense surfaces with uniform properties.
Co-authors
Jurgen Konys
(Institute for Applied Materials, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany)
Sven-Erik Wulf
(Institute for Applied Materials, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany)
Wolfgang Krauss
(Institute for Applied Materials, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany)
