Cr effect on hydrogen embrittlement of Fe3Al-based iron aluminide intermetallics: Surface or bulk effect

The objective of this work is to reduce the susceptibility of binary Fe3Al intermetallics to hydrogen embrittlement with the addition of chromium as the ternary element. The Young's modulus, Gibbs free energy for homogeneous dislocation nucleation (HDN) and velocity of dislocations were evaluated by an in situ nanoindentation method in air and under cathodic and anodic charging. The results show the influence of hydrogen on the reduction of Young's moduli of alloys, in agreement with the hydrogen-enhanced decohesion model, whereas measurements of the pop-in load indicate a drastic decrease after cathodic charging in samples with low Cr content. This is thought to be due to the decrease of the energy needed for HDN in the dislocation-free samples based on the defect-acting agents concept. Additionally, the effect of hydrogen on the mobility of dislocations and also the influence of Cr on the characteristics of passive oxide layer were analysed in detail. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.