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 measurement s of aluminised martensitic steels (F82H-mod. and MANET) under gaseous hydr ogen 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 exh ibited only a moderate PRF when tested under gaseous hydrogen tin compariso n to previously reported data) but an even lower PRF when tested under liqu id Pb-17Li/hydrogen, In particular, the coated MANET tube exhibited an incr easing 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 alumi nide coating should form alumina down to very low aluminium contents (x(Al) = 0.0133 in oxygen-saturated Pb-17Li at 773 K), they also show that the th ermodynamically favoured product is LiAlO2. (C) 2000 Elsevier Science B.V. All rights reserved.