The role of symmetric tilt grain boundaries on the precipitation of hydrides in zirconium: A molecular dynamics study.

Zirconium (Zr) alloys are widely used as structural materials in the core of nuclear reactors. However, the absorption of hydrogen by these alloys during the reactor operation may lead to the precipitation of hydrides. Such hydrides have considerable effects on the microstructure and mechanical properties of the alloys, thus significantly impacting their overall performance. In this work, we investigate the behavior of hydrogen in the presence of symmetric tilt grain boundaries in Zr using molecular dynamics simulations. To systematically explore the conditions for the formation of hydrides, we consider hydrogen concentration levels of up to 50 at.%. We find that hydrogen concentrations of 30 at.% or lower are below the threshold for the precipitation of hydrides, while fcc coordinated hydrides precipitate at 50 at.%, which is very close to the solubility limit of hydrogen in Zr at 800 K. We find that the grain boundaries (GBs) play a pivotal role in the behavior of hydrogen, as well as the formation of hydrides in Zr systems. In most cases, large amounts of hydrogen are found to accumulate at GBs. However, both homogeneous and heterogeneous nucleation are observed during the formation of hydrides at the grain interiors and GBs, respectively. Nonetheless, in some cases the GB inhibit the formation of hydrides. [ABSTRACT FROM AUTHOR]