<Abstrate>

In this work we consider three representative continuous coarsening processes,

namely subgrain growth in deformed subgrain structures, triple junction motion

in deformed lamellar structures, and grain growth in deformed nanocrystalline

structures, spanning a large range in structural scale and driving force. We propose a

unified coarsening model, which is based on recovery kinetics and allows the

apparent activation energy to change during coarsening. The model is successfully

applied to the three coarsening processes in different materials of different structural

morphology and scale, showing that the apparent activation energy increases during

coarsening, which is verified by direct calculation. The increase in the apparent

activation energy dominates the coarsening kinetics and leads to a significant decrease

in the coarsening rate as coarsening proceeds. This suggests that a conventional grain

growth model is not applicable in an analysis of coarsening of nanostructured materials.

Our analysis also shows that an initial low thermal stability of nanostructured materials

is inherently related to their large boundary area per unit volume and their high content

of stored energy, providing a large driving force and, it appears, a low activation energy

for structural coarsening.

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