Invited Lecture
Structural elements of polycrystal and evolution and stability of nanocrystalline materials

The influence of different structural elements of polycrystals - on the thermodynamics and kinetics of grainulars microstructure and their evolution and stability in nanocrystalline materials is considered.

The results of grain growth experiments in nanocrystalline films deposited on a substrate are discussed in the framework of a theoretical concept in which grain growth is accompanied by vacancy generation to compensate for the released excess volume. It is shown that the predicted “incubation time”, which precedes grain growth is also observed in experiment. The measured “incubation time” can be utilized to determine the grain boundary excess free volume. The results compare reasonably well to values obtained in experiments, where the pressure dependence of grain boundary energy was measured.

A general Gibbs-Thomson equation is derived from the complete free energy description of an inclusion at a grain boundary, taking into account the excess free energy of the grain boundary –phase boundary junction. It is shown that the equilibrium shape of the inclusion (particle or void) yields a strong dependency on the inclusion size, which gives rise to a deviation from the classical theory of precipitation. The influence of the line tension of triple junctions on the nucleation energy barrier is discussed.

The influence of grain boundary triple junctions on thermodynamics and kinetics of grains microstructure and its evolution and stability in nanocrystalline materials is considered.