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M: Metallphysik
M 36: Nanoskalige Materialien IV
M 36.7: Fachvortrag
Freitag, 30. März 2001, 12:30–12:45, S5.3
Grain boundary phase transitions and their influence on properties of poly- and nanocrystalline materials — •Boris Straumal1, Alexander Zhilyaev2, Yurii Kolobov3, and Hans-Eckhardt Schaefer4 — 1ISSP RAS, Chernogolovka, Russia — 2USATU, Ufa, Russia — 3ISPMS RAS, Tomsk, Russia — 4Universitaet Stuttgart
The properties of poly- and nanocrystalline materials depend hardly on the behaviour of grain boundaries (GBs) and GB phase transitions. The GB wetting phase transitions proceed in the two-phase area of bulk phase diagram where the liquid and solid phases are in equilibrium. They control the liquid phase sintering, deformation of materials in the semi-solid state, GB penetration of the liquid phase, various processes of soldering and joining. The GB prewetting and/or premelting phase transitions in the one-phase area of the bulk phase diagram where only the solid solution is in equilibrium lead to the formation of an equlibrium layer of a GB phase. This layer can possess a high diffusivity. Such GB phase transitions can control the stability of nanocrystalline structure and processes of hot cracking, activated sintering, superplasticity, GB brittleness, formation of nanocrystalline structure from the amorphous state. The financial support of the INTAS Programme and Alexander von Humboldt Foundation is acknowledged.