Synchrotron radiation topographic study of slip transfer across grain boundaries in Fe-Si bicrystals

摘要

The transfer of the common slip system across grain boundaries was examined. Bicrystals of alloys Fe-Si with Si content 4 and 5.5 at% were used for both tension and compression straining. The progress of the deformation was followed by synchrotron radiation diffraction topography after straining and under increasing external stress. An x-ray sensitive camera was used for recording the topographs in addition to the classical technique using photographic plates. Three slightly different settings with different sensitivities to interplanar spacing (deformation) and orientation variations of the adjacent crystal regions were applied. The movement of the slip bands was followed. A distortion of the image appeared at the grain boundary when the slip bands stopped there and decreased or nearly disappeared when the slip bands crossed it after an increase in the applied stress. The distortion is explained by elastic deformation around the heads of the slip bands stopped at the boundary. True slip transfers are differentiated from the false ones by observing elastic deformation in early deformation stages and by optical observation of slip pattern after deformation. The transfer of the common slip system across a twin boundary, whereas expected to be direct, required stress accumulation. The twin boundary proved to be a real barrier. The results obtained for specimens with different Si content were compared.