Hydride precipitates in zirconium alloys: Evolution of dissolution and precipitation temperatures during thermal cycling correlated to microstructure features

Abstract

The fast and spontaneous hydrogen diffusion in zirconium alloys used in the nuclear industry leads to the hydride precipitation which is often pointed as causing embrittlement and rupture. Our studies using X-ray Diffraction (XDR), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy coupled to Back-Scatter Diffraction (SEM-EBSD) have been demonstrating that the nature of the hydride phase precipitate depends on the hydrogen content, and can show crystallographic orientation relationships (ORs) with the substrate. Differential Scanning Calorimetry (DSC) has been used to identify the dissolution and precipitation energies at global scale. The difference of both can be associated to the misfit dislocations contribution to the precipitation. Local In-situ TEM dissolution observations confirm the dissolution temperature identified at a global scale and show the depinning of some misfit dislocations during dissolution process. The consequence of this mechanism is that dissolution and precipitation temperatures shift during thermal cyclic loading. This situation will be correlated to the nature of crystallographic hydride phases and their ORs.