Corrosion behavior and mechanisms of Al2O3 and Mo coated Zircaloy-4 in high-temperature lithiated water

Abstract

Anti-corrosion coatings on Zircaloy cladding have been extensively explored to guarantee the safe operation and scale up industrialization of nuclear reactors. In this work, Mo and Al2O3 powders were successfully coated on Zircaloy-4 by air plasma spraying. Their morphologies, phases of corrosion products and hardness were analyzed. After exposure to lithiated water at 360 °C and 18.5 MPa for 500 h, Mo coating fell off and complex phases were formed on the residual bonding layer. The corrosion products were NiO(OH), MoO3, Mo sub-oxides, ZrO2, Zr sub-oxides, Al2O3, intermetallic Ni-Al compound, Li2Ni2(MoO4)3, NiCr2O4 and NiFe2O4. Corrosion mechanism of Al2O3 coating was discussed in details. Cracks and pores evolved on the coating, and the surface phases were dominantly Al2O3 and AlO(OH). ZrO2, SnO, intermetallic Zr-Al, Ni-Al-O, Li-Al-O, NiFe2O4 and NiCr2O4 were also detected in the presence of LiOH.