Deformation processing of massive nanostructured materials

Deformation processing of initially polycrystalline material can lead to ultrafine-grained or even to nanocrystalline material, depending on the applied deformation route. In addition to different grain sizes, materials processed by different deformation methods also display different thermal stabilities. In order to analyze the impact of defects - particularly dislocations - near the grain boundaries, pure Pd and pure Ni have been processed sequentially by different methods. Transmission electron microscopy investigations at high resolution were conducted to characterize the microstructures of the materials. In addition, geometrical phase analysis was used to locate defects and visualize their strain fields. The results indicate that the presence of a high dislocation density at the grain boundaries increases the stability of the nanocrystalline structure against coarsening.