In situ formation and chemical stability of Er 2O 3 coating on V–4Cr–4Ti in liquid lithium

Abstract

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 Er 2O 3 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 Er 2O 3 and an intermediate layer of mixed ErN and V-compounds. The Er 2O 3 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.