Two-dimensional vacancy platelets as precursors for basal dislocation loops in hexagonal zirconium

Zirconium alloys are widely used structural materials of choice in the nuclear industry due to their exceptional radiation and corrosion resistance. However long-time exposure to irradiation eventually results in undesirable shape changes, irradiation growth, that limit the service life of the component. Crystal defects called < c > loops, routinely seen no smaller than 13nm in diameter, are the source of the problem. How they form remains a matter of debate. Here, using transmission electron microscopy, we reveal the existence of a novel defect, nanoscale triangle-shaped vacancy plates. Energy considerations suggest that the collapse of the atomically thick triangle-shaped vacancy platelets can directly produce < c > dislocation loops. This mechanism agrees with experiment and implies a characteristic incubation period for the formation of < c > dislocation loops in zirconium alloys. Zirconium alloys are widely used in the nuclear industry, but long-time irradiation leads to shape changes and irradiation growth that relate to basal dislocation loops in zirconium. Here the authors discern nanoscale triangle-shaped vacancy platelets in helium-irradiated zirconium, which are a precursor of basal dislocation loops.