Abnormal corrosion behavior of TaTiZr medium-entropy alloy coated stainless steel in liquid lead-bismuth alloy

• Coated steel exhibits severe LBE corrosion due to the penetration of O-depleted LBE compared to bare steel. • TaTiZr coating with high oxygen affinity enables the mass dissolved oxygen to uniformly diffuse. • Oxidized TaTiZr coating maintains stable amorphous structure as oxygen inhibits the long-range diffusion of metallic atom. In this work, corrosion dynamics of TaTiZr amorphous medium-entropy alloy (AMEA) coated 15-15Ti austenitic stainless steel were investigated in liquid lead-bismuth eutectic (LBE) with an oxygen concentration of 5×10 −7 wt.% for 500–1500 h at 550°C. Compared to bare steel, the coated sample unexpectedly exhibited inferior corrosion resistance. It is attributed to the cracking and peeling off of the coating due to the large coefficient of thermal expansion mismatch stress, which allows inward penetration of LBE. Owing to the high oxygen affinity of TaTiZr coating, the penetrated LBE contains insufficient oxygen content to facilitate the formation of protective oxide scales on teel surface, giving rise to severe dissolution corrosion, with depth of corrosion increasing over time. However, TaTiZr coating maintained a stable amorphous structure without phase transformation or consumption, though it showed noticeable thickening due to the dissolution of massive oxygen. Our findings are expected to promote understanding of potential failure of AMEA coated claddings in LBE.