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International audienceThe corrosion mechanisms by liquid aluminum of three industrial materials have been studied: unalloyed steel (UAS), and ferritic and modified pearlitic cast irons (FCI and PCI, respectively). The behavior of these materials when in contact with liquid aluminum is different. Aluminum diffuses deep into the UAS and forms intermetallic compounds with iron at the surface and in the steel matrix. At the surface, only Fe2Al5 and FeAl3 are found. In the matrix, FeAl2 also is formed in agreement with the equilibrium Fe-Al diagram. From the matrix to FeAl2, the Al content in the ferrite increases progressively until Al saturation is reached. At this step, black elongated precipitates (Al4C3 and/or graphite) appear. Graphite lamellas present in both FCI and PCI constitute an efficient barrier to the Al diffusion. The high silicon content of the FCI leads to the formation of a phase free from Al and saturated in Si. For the PCI, a thin layer rich in Al and Si, which is formed between the matrix and Fe2Al5, limits the diffusion of atoms. The effects of Cr and P added in the PCI also are discussed

15The corrosion of an austenitic steel in liquid sodium containing 189 µg.g -1 of oxygen was 16 investigated at 650°C as a function of time (122, 250 and 500 h). The steel samples were 17 characterized by means of complementary techniques, namely scanning electron microscopy, X-18 ray diffraction, glow discharge optical emission spectroscopy and transmission electron 19 microscopy. The characterizations showed that a NaCrO 2 oxide scale forms at the steel surface. 20Under this oxide scale, iron and molybdenum rich M 6 C carbide particles together with NaCrO 2 in 21 the grain boundaries and cavities filled with sodium were observed. The stainless steel substrate 22 and / or the chromite scale were dissolved in parallel with the formation of chromite and carbides. 23Thermodynamic calculations showed that NaCrO 2 and M 6 C are equilibrium phases in such a 24 system. NaCrO 2 is formed by the reaction of chromium diffusing from the steel bulk with sodium 25 and dissolved oxygen (external selective oxidation). Mo segregates to the steel surface where it 26 reacts with Fe from the steel and C dissolved in liquid sodium. The dissolution of stainless steel 27 occurred since the liquid sodium bath is not saturated in the dissolving species (pure metals and 28 oxides such as NaCrO 2 , Na 4 FeO 3 ). As for the cavities, vacancies are created at the steel / NaCrO 2 29 interface by Cr oxidation, carburization and dissolution of the other elements present in the 30 stainless steel. The vacancies become supersaturated and this leads to the nucleation of the 31 cavities observed. Part of the vacancies created by Cr oxidation or steel dissolution is annihilated 32 at sinks like dislocations leading to the translation of the oxide / metal interface towards the metal 33 bulk. 34