It was noted that bulk nanostructured metals were often formed via severe plastic deformation. The dislocations which were generated during severe plastic deformation evolved into boundaries and decomposed the grains. Vacancies were also produced in large numbers during severe plastic deformation, but had received much less attention. Here, by using transmission electron microscopy, a high density of unusually large vacancy Frank loops in severe plastically deformed Al was demonstrated. They were shown to impede moving dislocations, and thus contribute to strength.

Vacancy Clusters in Ultrafine Grained Al by Severe Plastic Deformation. X.L.Wu, B.Li, E.Ma: Applied Physics Letters, 2007, 91[14], 141908