Hydride precipitation dependence on α-parent orientation and plastic deformation in zirconium alloys

Hydrides are at the center source of mechanical degradation affecting Zr-based nuclear fuel cladding integrity during in-reactor service and even spent fuel storage. This study presents investigations on hydride precipitation in response to thermo-mechanical treatment in a hydrogenated Zircaloy-4 plate. Correlated EBSD and ECCI characterizations demonstrate stress-induced variations in α-parent orientation and stacking structure between the in-plane and reoriented hydrides. Based on the hydride strains quantified by HR-EBSD, external tensile stress is found to favor the α-grains submitted to significant {0001}<10-10> shear stress as preferential nucleation sites for reorientated hydrides. Regardless of elastic or plastic stress, the interaction between external stress and hydride strains, particularly the shear component, is expected to govern hydride nucleation probability as a function of α-grain orientation and eventually induce hydride reorientation. Influence of plastic deformation is mainly manifested in hydride distribution, where the {10-10}<11-20> slipping promotes reoriented hydride interconnection up to hundreds of microns while the {10-11}<10-1-2> twining results in a fragmented distribution, as visualized by X-ray tomography. The presented results provide solid experimental evidences for the auto-catalytic nucleation and martensitic transformation of hydride precipitation, as well as new insights into stress-induced hydride reorientation in the light of stress interaction with hydride strain.