The effect of coatings on the compatibility of Fe–Cr steels with Pb–Li

To inhibit the dissolution and mass transfer of ferritic–martensitic steels in Pb–Li above 500 °C, the behavior of Al-rich diffusion coatings was explored in isothermal capsule exposures. After 1 kh at 600 °C or 700 °C, thin (∼40 μm) coatings made by chemical vapor deposition significantly reduced the mass loss of commercial Fe–9Cr–2 W substrates. At both temperatures, the surface reaction product was LiAlO2 but at 700 °C a significant Al depletion occurred in the coating reducing the surface Al content from ∼18 at.% to <9%. Several strategies were explored to reduce the Al depletion from the coating including pre-oxidizing the coating before Pb–Li exposure and exposure to pure Pb. In each case, the Al loss was similar, suggesting that Al is being lost to the liquid metal despite the formation of an external oxide layer. Thicker coatings or Al alloy additions are potential solutions for operation at >600 °C.