Hydride embrittlement and irradiation effects on the hoop mechanical properties of pressurized water reactor (PWR) and boiling-water reactor (BWR) ZIRCALOY cladding tubes: part II. Morphology of hydrides investigated at different magnifications and their interaction with the processes of plastic deformation

This series of articles on hydride embrittlement effects in ZIRCALOYs consists of three parts. In Part II, the morphology of hydrides in two ZIRCALOYs has been examined at different magnifications and by different techniques (scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD)). The purpose is to establish the correlation between the hydride morphology and the microstructure of the ZIRCALOYs as a function of their pre-heat treatment and their hydrogen content. It was found that in these alloys microstructure has a very significant effect on the size, the stacking pattern, and the location of hydrides. The hydride morphology and its evolution with increasing hydrogen content was not the same in the stress-relieved annealed (SRA) and the recrystallized ZIRCALOYs. These observations were then correlated with the damage mechanisms of the hydrided ZIRCALOYs. Part I, concerned with the general influence of hydride on the mechanical properties of ZIRCALOYs and the damage and fracture mechanisms. Part III, on the other hand, discusses the mechanical properties of the hydrides themselves under the influence of several parameters.