We investigated hydrogen embrittlement and blistering in electrochemically hydrogen-charged technical iron samples at room temperature.
Hydrogen-stimulated cracks and blisters and the corresponding hydrogen distributions were observed by neutron tomography.
Cold neutrons were provided by the research reactor BER II to picture the sample with a spatial resolution in the reconstructed threedimensional
model of 25 lm. We made the unique observation that cracks were filled with molecular hydrogen and that cracks were
surrounded by a 50 lm wide zone with a high hydrogen concentration. The zone contains up to ten times more hydrogen than the bulk
material. The hydrogen enriched zone can be ascribed to a region of increased local defect density. Hydrogen also accumulated at the
sample surface having the highest concentration at blistered areas. The surfaces of the brittle fractured cracks showed micropores visualized
by scanning electron microscopy. The micropores were located at grain boundaries and were surrounded by stress fields detected
by electron backscattered diffraction. The cracks clearly originated from the micropores.
2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keywords: Hydrogen embrittlement; Hydrogen diffusion; In situ; Neutron tomography; Iron
1. Introduction
The durability of alloys can be influenced significantly
by hydrogen uptake, leading to a degradation of the
mechanical properties with possible subsequent hydrogenassisted
cracking (HAC) [1,2]. In numerous investigations,
different factors affecting the hydrogen embrittlement have
been studied, e.g. hydrogen content [3], residual stress and
strain due to internal or external forces [4] and microstructure
[5]. All these factors can lead to a critical condition for
hydrogen embrittlement