In situ formation and chemical stability of Er2O3 coating on V–4Cr–4Ti in liquid lithium

An electrically insulating coating is under development to mitigate magneto-hydrodynamic (MHD) pressure drop in self-cooled Li/V-alloy blanket. A previous study showed the feasibility of in situ formation of an Er2O3 coating by exposing V–4Cr–4Ti to liquid Li doped with Er at high temperature. In this paper, the characteristics and the long-term stability of such a coating were investigated. A V–4Cr–4Ti substrate was oxidized in flowing Ar at 973 K, annealed in vacuum at 973 K and finally exposed to liquid Li doped with Er from 773 to 973 K. The oxygen charged and homogenized at the surface of the substrate that acted as a source for coating formation. The surface layer formed on V–4Cr–4Ti consists of double sub-layers, namely an insulating coating of Er2O3 and an intermediate layer of mixed ErN and V-compounds. The Er2O3 coating was found stable up to 750 h of exposure time in liquid Li at 873 K with its saturated thickness of ∼0.1 μm. The coating was stable up to 300 h at 973 K with its thickness increased to ∼1.2 μm. Cracks were observed in coatings formed at 923 and 973 K. The mechanism of cracking is under investigation.