Characterization of alumina coatings on Eurofer97 steel

The increasing energy demand together with the need to replace fossil fuels as primary energy sources, leads the research to find more sustainable options. Among them, the nuclear energy is one of the most competitive alternatives, because it is able to produce energy without emitting greenhouse gasses. There are two categories for this source: fission and fusion. Essentially, the first divides a heavy nucleus in two lighter ones and the second vice versa, both releasing a large amount of energy. One of the main issues in the construction of nuclear fusion reactors, such as the European DEMO, is related to the material composing the breeding blanket. This is an essential part, since it provides tritium: the fuel necessary for the operation, while facing an extreme environment. The structural material for fusion reactors is Eurofer97, which has good resistance to radiation, but is sensible to embrittlement caused by neutron irradiation and hydrogen isotopes permeation. Moreover, the steel suffers corrosion by the PbLi eutectic. For these reasons, it is essential to protect the structural material with a barrier. During this thesis work at the C.R. ENEA of Brasimone, alumina deposited by PLD (Pulsed Laser Deposition) technique, was taken into account due to its stability at high temperature in the PbLi environment. In fact, the specimens were analyzed before and after exposure tests at 550°C for 1000, 4000 and 7000 hours in static PbLi (eutectic alloy), used as breeder and neutron multiplier in the breeding blanket type WCLL (Water-cooled Lithium Lead). Furthermore, two different thicknesses 3 µm and 5 µm were considered, in order to identify the sufficient one for operation. The samples with 3 µm-thick coatings were also annealed in air for 75 hours at 550°C, inside a furnace. The coating was investigated in terms of both microstructure and composition, using optical and electron microscopy, EDS analysis and XRD (X-ray diffraction).