Hydrogen is the most abundant element,both in the universe and on earth. As an element with the simplest atomic structureand smallest volume, hydrogen can easily dissolve into many solid materials,changing their properties. In many industrially important metals during processingor service, hydrogen often has deleterious consequence on mechanical propertiesthat is commonly referred to as hydrogen embrittlement (HE), thus has been a wideconcern in industry and academia for over a century.
Despite numerous efforts over thepast century, the exact mechanism of hydrogen effects on the ability of thematerial to plastically deform remains controversial, thus knowing how hydrogeninteracts with dislocation – the primary carriers of plasticity is essential. Dueto its high diffusivity, hydrogen is often considered a weak inhibitor or evena promoter of dislocation movements in metals and alloys.
But our latest experimental discoverysubverts the established cognition in the past decades.
The effect of vacuum aging on dislocation movements inhydrogen-free sample
Effectof hydrogenation on dislocation movements.
By quantitative mechanical tests inan environmental transmission electron microscope, here Dr. Degang Xie, a youngfaculty in CAMP-Nano, demonstrates that after exposing aluminium to hydrogen, mobiledislocations can lose mobility, with activating stress more than doubled. Ondegassing, the locked dislocations can be reactivated under cyclic loading tomove in a stick-slip manner. However, relocking the dislocations thereafterrequires a surprisingly long waiting time of ~103s, much longer thanthat expected from hydrogen interstitial diffusion. Both the observed slowrelocking and strong locking strength can be attributed to superabundanthydrogenated vacancies, veriﬁed by our atomistic calculations. Vacancies thereforecould be a key plastic ﬂow localization agent as well as damage agent inhydrogen environment.
Side view of dislocation core decorated byhydrogen and hydrogen-vacancy complex, respectively. Atoms with golden andblack colours refer to aluminum and hydrogen, respectively
Atomisticsimulation of the pinning effect of hydrogen-vacancy
The project is supervised by Prof.Zhiwei Shan and Prof. Ju Li. Besides vice Prof. Zhangjie Wang and Dr. Meng Lifrom our faculty and post Dr. Suzhi Li,Prof.PeterGumbsch, Prof. Jun Sun, Prof. Evan Ma also made a significant contribution tothis work.
This work has been published on thetop research journal, Nature Communications.
The article can be accessed athttp://www.nature.com/articles/ncomms13341