Enhancing LBE corrosion resistance through inhibition diffusion approach for AlTixCrFe HEA coating

Abstract

High-entropy alloy (HEA), when used as coating materials for structural steel in lead–bismuth eutectic (LBE) nuclear reactor, faces severe dissolution corrosion due to the diffusion of their constituents along grain boundaries. In order to mitigate dissolution corrosion, a method to enhance the LBE corrosion resistance of HEA is proposed by utilizing a second phase to inhibit elemental diffusion at grain boundaries. Herein, we used the laser cladding technique to prepare a series of biphase AlTixCrFe HEA coating with a body-centered cubic primary phase and a TiAl second phase. During the LBE corrosion process, a single-layer oxide layer (OL) formed on the HEA coating surface, and meanwhile there existed an internal oxidation zone (IOZ) formed beneath the single-layer OL at AlTixCrFe HEA coating interface, which gradually converted into the single-layer OL as the corrosion time prolonged. After 2000 h of corrosion, AlTi0.75CrFe HEA coating exhibited the lowest OL thickness (8.1 μm) and oxidation rate (0.065 μm2/h) because Al, Ti, and Cr acted as protective elements, rapidly forming a protective OL on the surface. Meanwhile, the presence of TiAl second phase at the grain boundaries impeded the mobility of elements, which improved the dissolution corrosion resistance and diminished its destructive impact on the protective OL.