Mechanisms of Mesoscale Hydride Morphology and Reorientation in a Polycrystal Investigated Using Phase-Field Modeling

This study focuses on the precipitation of nanoscale hydrides in polycrystalline zirconium as a first step to predicting the hydride morphology observed experimentally and investigating the mechanisms responsible for hydride reorientation at the mesoscale. A quantitative phase-field model, which includes the elastic anisotropy of the nanoscale zirconium hydride system, is developed to investigate the mechanism of hydride reorientation in which the presence of an applied hoop stress promotes hydride precipitation in grains with basal poles aligned with the circumferential direction. Although still elongated along the basal plane of the hexagonal matrix, nanoscale hydrides growing in grains oriented perpendicular to the applied stress appear radial at the mesoscale. Thus, a preferential hydride precipitation in grains with basal poles aligned parallel to the applied stress could account for mesoscale hydride reorientation. This mechanism is consistent with experimental observations performed in other studies.