IN-SITU OBSERVATION OF PLASTIC-DEFORMATION OF FE-SI BICRYSTALS BY WHITE-BEAM SYNCHROTRON-RADIATION TOPOGRAPHY

In-situ experiments using synchrotron X-ray topography have been carri ed out in order to study dislocation transmission through grain bounda ries in bicrystals of Fe-4at.% Si alloy in the initial stage of plasti c deformation. The grain boundaries hinder dislocation motion even in case of the most favourable slip geometry. that is when both Burgers v ectors and slip planes are parallel in the two grains. The slip transm ission is greatly affected by the stresses exerted by dislocations sto pped at the grain boundaries and by the local structure of the grain b oundary itself. The slip behind the boundary starts most probably from new dislocation sources formed under combined external and internal s tresses.