A Review of Recent Advance on Hydrogen Embrittlement Phenomenon Based on Multiscale Mechanical Experiments

Hydrogen is widely considered to be one of the future clean energy sources. A large scale of production, storage, transportation, and the use of hydrogen-related energy is likely to be escalated in the next few decades. However, the presence of hydrogen seriously deteriorates the mechanical properties of most structural metals, which is a main threat to the hydrogen economy. Although hydrogen embrittlement has been recognized for more than a century, there is still a lack of effective measures to elimi- nate this embrittlement in the engineering practices and some aspects of fundamental science; the embrittlement mechanism is still poorly understood. Because hydrogen is the lightest element in the universe, it exhibits several unique characteristics like permeability, fast diffusion, and unstable distribution in different scale defects. These characteristics are seriously affected by external stress, temperature, and other environmental factors. Therefore, the drawback of hydrogen embrittlement is still an extremely complex and attractive scientific topic. In the last two decades, with the development of multi-scale mechanical experimental techniques, various new studies on hydrogen embrittlement have been reported and its mechanism is deeply evaluated. Based on these advances, this review reflects on the complexity and importance of this topic. The macro-mechanical tests such as constant load and slow strain rate tensile tests are presented and their advantage and disadvantage on screening the susceptibility of materials to hydrogen embrittlement are compared. Subsequently, the hydrogen-indentation (hardness) method is introduced at the mesoscale to show the hydrogen-induced cracking and its application. Furthermore, the main focus of this review comprises the modern experimental approaches to fine-scale evaluation of the hydrogen-dislocation interaction, with particular emphasis on the nanoindentation pop-in effect, micro-pillar compression and micro-cantilever bending tests, and environmental transmission electron microscope tests. The fundamental principles of these approaches are overviewed, and their contribution to the elucidation of the hydrogen embrittlement mechanism is discussed. For example, the different effects of hydrogen on the mechanical properties and a mechanism similar to the hydrogen effect are proposed based on the micro-pillar compression and micro-cantilever bending tests. Nevertheless, there are still several discrepancies in the hydrogen-dislocation interaction that needs further investigation.

Automated summary

Hydrogen is considered a future clean energy source, but its presence deteriorates the mechanical properties of most structural metals, resulting in hydrogen embrittlement whose mechanism is not fully understood. With advances in technology, research on hydrogen embrittlement is progressing, but there are still discrepancies that need further investigation.