In-situ observation of Migrating grain boundaries in Au-Bicrystals

The understanding of the migration of grain boundaries in metals is the basic step for understanding the microstructure development during recrystallization. Bicrystals of Gold with different tilting angle were produced by depositing Au-layers on top of seed-crystals.

The bicrystals were studied in the HRTEM by recording the atomic motion on a video. Although in this experiment there was no driving force, the atoms gradually leave their positions in one grain and jump to the other side of the grain boundary. This back and forth motion on atomic scale is a vibration of the boundary plane on macroscopic scale.

The analysis of this experiment showed that grain boundaries can be divided in four different types. Each of these types have a different vibration frequency and mobility.

Using a heating stage in conventional TEM the motion of boundaries was studied on a mesocopic scale. In this experiment the driving force is the reduction of the grain boundary area. The results showed a jerky motion of the boundary. The velocity of each segment was about 10 time faster than the average velocity.

References:

W. Wunderlich,
Theoretical considerations about Grain Boundary Migration in fcc Metals,
Mat. Sci. Forum [207] (1996) 141-144 (Proc. iib’95 Lisboa 1995) pdf-file 467kB
Keywords: Atomic structure of grain boundaries, activation energy of grain boundaries, mobility, recrystallization, in-situ HRTEM

G.Gottstein, U. Czubayko, D.A. Molodow, L.S. Shvindlerman, W.Wunderlich,
In-situ Observations of Grain Boundary Migration,
Material Science Forum [204-206] (1996) 99-108 (Proc. ICGG II Japan 1995) pdf-file 1.3MB
Keywords: Migration of grain boundaries, mobility, XICPD, activation energy, HRTEM image

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