In-situ measurement of annealing kinetics of individual bulk grains in nanostructured aluminium

Non-destructive three-dimensional X-ray diffraction (3DXRD) was used to characterise the coarsening and growth of bulk crystallites in very heavily deformed aluminium in-situ during isothermal annealing. It was found that initially during the annealing, coarsening by recovery dominates. Later recrystallisation starts and, by fast growth of recrystallisation nuclei, some very big grains evolve.

This occurs simultaneously with recovery coarsening of other parts of the microstructure. Consequently, very broad grain size distributions are observed. The 3DXRD results show that the nuclei (those crystallites that end up being very large by fast recrystallisation growth) do not have an initial size advantage compared to those coarsening much slower by recovery.

Kinetics curves for these two categories of grains are determined. Data of this type are considered very important for understanding the thermal response of nanometals and thus also for instructing thermal treatment for optimal mechanical properties.