The hydrogen permeation behaviour of aluminised coated martensitic steels under gaseous hydrogen, liquid Pb–17Li/hydrogen and cyclic tensile load

This paper describes the results of in-situ hydrogen permeation measurements of aluminised martensitic steels (F82H-mod. and MANET) under gaseous hydrogen and liquid Pb–17Li/hydrogen while being subjected to a cyclic tensile load. The results are presented in terms of the permeation reduction factor (PRF) of the coating. The vacuum plasma sprayed (VPS) coated specimens exhibited only a moderate PRF when tested under gaseous hydrogen (in comparison to previously reported data) but an even lower PRF when tested under liquid Pb–17Li/hydrogen. In particular, the coated MANET tube exhibited an increasing permeation rate with time for sequential measurements carried out at 830 K, which was attributed to the effect of wetting of the surface by the Pb–17Li. Although thermodynamic calculations have indicated that the aluminide coating should form alumina down to very low aluminium contents (xAl=0.0133 in oxygen-saturated Pb–17Li at 773 K), they also show that the thermodynamically favoured product is LiAlO2.