Temperature-dependent degradation of Al2O3—CrAl-O—Cr-O—Al-O multilayer coatings on ferritic-martensitic steels in oxygen-saturated lead–bismuth eutectic

• Corrosion behavior of Al-O—Cr-O—CrAl-O—Al 2 O 3 multilayer coatings was investigated. • Al 2 O 3 outer layer blocks lead–bismuth eutectic diffusion while α-(Cr,Al) 2 O 3 sublayer synergistically suppresses oxygen penetration at 650 °C. • The holes in Cr-O layer were most at risk for further deteriorating the coating. The strong corrosiveness of lead–bismuth eutectic (LBE) to alloys significantly limits the development of lead-cooled fast reactors. Herein, a multilayer coating containing Al-O, Cr-O, CrAl-O, and Al 2 O 3 layers were deposited on ferritic–martensitic steel using magnetron sputtering and tested in oxygen-saturated LBE at 450, 550, and 650 °C for 2000 h. The phase transformation and microstructural evolution of the coating, owing to temperature and element diffusion, were characterized in detail at the microscale. At 450 °C, the Al 2 O 3 layer partially transformed to δ*-Al 2 O 3 and PbAl 2 O 4 , while the Cr-O layer crystallized into Cr 2 O 3 . At 650 °C, γ-Al 2 O 3 transitioned to α-Al 2 O 3 , and a dense α-(Cr,Al) 2 O 3 phase formed at the CrAl-O/Al 2 O 3 interface, effectively blocking LBE penetration. Despite full infiltration of the Al 2 O 3 layer at 650 °C, the CrAl-O interlayer suppressed elemental interdiffusion, maintaining substrate integrity. Temperature-dependent degradation revealed critical failure at the Cr-O layer due to MnCr 2 O 4 -induced porosity. The multilayer coating maintained a relatively good integrity at high temperatures and protected the substrate from LBE corrosion.