Three mechanisms of hydrogen-induced dislocation pinning in tungsten

Abstract

The high-flux deuterium plasma impinging on a divertor degrades the long-termthermo-mechanical performance of its tungsten plasma-facing components. A prime actor inthis is hydrogen embrittlement, a degradation phenomenon that involves the interactions between hydrogen and dislocations, the primary carriers of plasticity. Measuring such nanoscaleinteractions is still very challenging, which limits our understanding. Here, we demonstrate anexperimental approach that combines thermal desorption spectroscopy (TDS) andnanoindentation, allowing to investigate the effect of hydrogen on the dislocation mobility in tungsten. Dislocation mobility was found to be reduced after deuterium injection, which ismanifested as a ‘pop-in’ in the indentation stress-strain curve, with an average activation stressfor dislocation mobility that was more than doubled. All experimental results can be confidentlyexplained, in conjunction with experimental and numerical literature findings, by the simultaneous activation of three mechanisms responsible for dislocation pinning: (i) hydrogentrapping at pre-existing dislocations, (ii) hydrogen-induced vacancies, and (iii) stabilization ofvacancies by hydrogen, contributing respectively 38%, 52%, and 34% to the extra activationstress. These mechanisms are considered to be essential for the proper understanding and modeling of hydrogen embrittlement in tungsten.