Hydrogen enhanced cracking studies on Fe–3wt%Si single and bi-crystal microcantilevers

Abstract

Hydrogen (H) enhanced cracking was studied in Fe-3wt%Si by means of electrochemical microcantilever bending test. It was clearly shown that the presence of H causes hydrogen embrittlement (HE) by triggering crack initiation and propagation at the notch where stress concentration is existing. Additionally, the effect of carbon content and the presence of a grain boundary (GB) in the cantilever were studied. It was shown that in the presence of H the effect of carbon atom on pinning the dislocations is reduced. On the other hand, the presence of a GB, while the chemical composition of material kept constant, will promote the HE. Crack initiation and propagation occur in the presence of H, while the notch blunting was observed for both single and bi-crystalline beams bent in air. Post-mortem analysis of the crack propagation path showed that a transition from transgranular fracture to intragranular fracture mechanism is highly dependent on the position of the stress concentration relative to the GB.This article is part of the themed issue 'The challenges of hydrogen and metals'.

Hydrogen-enhanced fatigue crack growth behaviors in a ferritic Fe-3wt%Si steel studied by fractography and dislocation structure analysis

“…A rather limited fraction of IG type fracture indicated that grain boundaries (GBs) were not significant vulnerable places for this material when subjected to H environment. This was confirmed in a previous work by Hajilou et al [55] that the GB in Fe-3wt%Si was not a favored path for crack growth after their test of bending a micro-cantilever with a notch on a GB. They found that the crack generated from the notch would rather propagate along the direction with the highest degree of stress concentration rather than along the GB, whether in vacuum or in H environment.…”

“…Since fatigue crack generally grows via ductile mechanisms even along a microstructural interface, it is reasonable to think that IG fracture is even more difficult in the FCGR testing. Furthermore, the dimension of the micro-cantilever testing in [55] can roughly present the case of a single cycle in the present FCGR testing. From these aspects, it is assumed that the GB in the investigated material has a relatively good resistance against IG cracking both in H-free and in H-charged environments.…”

Mechanisms of hydrogen embrittlement in steels: discussion

“…In summary, these remarks raise the following questions: For a long time, until today, I thought that the mechanisms in zirconium and titanium were different to those in a steel or a nickel alloy. Seeing the Norwegian work presented earlier on microcantilevers in steels (see [18]), you did appear to see plasticity around a crack tip in the cantilever. That was really interesting; even in a steel you do seem to see some evidence for a localized plasticity mechanism.…”

The Effect of Hydrogen on the Nanoindentation Behavior of Heat Treated 718 Alloy

“…To eliminate the crystallographic orientation dependency, a similar grain orientation of {101} was selected according to the orientation imaging map (OIM) of the samples. In situ electrochemical nanoindentation was performed using the Bruker TI 950 TriboIndenter system, which was integrated with a custom, three electrode miniaturized electrochemical cell [6]. The electrochemical setup consisted of counter, working, and Hg/HgSO 4 reference electrodes.…”