Influence of steel on the mechanical stress development during hydrogen-loading of ultrathin Nb-films

Thin films attached on rigid substrates can develop ultra-high compressive stresses upon hydrogen-loading. These high stresses can be released by dislocation-formation or delamination. For niobium thin films dislocation-formation was observed for films thicker than 6 nm upon hydrogen-loading up to 1 H/Nb. By alloying niobium with steel the critical film thickness for dislocation formation can be increased to at least 37 nm. TEM and EELS studies on the film's microstructure and elemental distribution show Fe-enriched regions being present at grain boundaries. This refines the hydrogen-absorbing Nb grain sizes thereby hardening the material.