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Abstract

Interfaces in metallic micro- and nanostructures play a role during plastic deformation in many respects. Besides accomodating part of the plastic strain by means of grain boundary sliding and migration they can act as sources, sinks, or barriers for dislocations, as well as as crack nucleation sites. Especially in interface dominated microstructures such as lamellar TiAl, they thus can rule the overall mechanical behaviour. High resolution experimental methods exist to analyze the underlying atomistic processes. However, since these processes are not independent, often several of them occur at the same time. To isolate the intrinsic deformation mechanisms of grain boundaries we have carried out molecular statics and molecular dynamics simlations of bicrystal shear at different interfaces in Al and TiAl. Four distinct mechanisms could be identified, namely rigid grain sliding, grain boundary migration, coupled sliding and migration, and dislocation nucleation and emission. Depending on the loading direction different mechanisms can occur at one and the same grain boundary, i.e. there is a pronounced anisotropy in the interfacial shear behaviour. This anisotropy is suggested as the explanation for seemingly contradicting experimental results (e.g. Marketz 2003, Hsiung 1999). By varying the geometry and chemistry of the interfaces we could relate the observed mechanisms to structural features of the grain boundaries as well as physical properties of the material. The influence of external factors such as strain and temperature will be discussed in the presentation. [1] W.Marketz, F.Fischer, and H.Clemens, ``Deformation mechanism in TiAl intermetallics - experimental and modeling'', Int. J. Plasticity, vol. 19, pp. 281-321, 2003. [2] L.Hsiung and T.Nieh, ``Creep deformation of fully lamellar TiAl controlled by the viscous glide of interfacial dislocations'', Intermetallics, vol. 7, pp. 821-827, 1999.