The Topography and Chemistry of Grain Boundary Fracture Surface in Dilute Fe-Si Alloy Bicrystals

Abstract

In the case of grain boundaries, the relation between the structure and segregation seems to be more complicated in comparison to free surfaces. Atomic structures of grain boundaries and hence the positions for segregating atoms depend on various factors, such as the disorientation of component crystals, the orientation of the boundary surface etc. Low segregation has been found on some special grain boundaries having a dense atomic arrangement. On the other hand, the level of phosphorus segregation at grain boundaries in α-Fe depends only on Miller indices of the measured boundary surface in similar manner as the surface segregation. Various structural features are visible at the fracture surface along the asymmetrical grain boundary. Some of them (deformation twins and cleavage tongues) originate during fracture process. They do not differ from those found at the {013} symmetrical boundary. Similarly, the steps occur also at the asymmetrical boundary with the same height and spacing. The fracture surfaces of both types of boundaries differ in the extensive twinning at the asymmetrical boundary. It is supposed that these twins occurred after the stresses at the grain boundary were released by the boundary separation. The {0 20 23} surface (near to the {011}) seems to be more favorable for this kind of twinning, while both to {0 1 14} (near to the {001} and {013} are not. The less pronounced segregation behavior of the asymmetrical {0 1 14}/{0 20 23} boundary in comparison with the {013} symmetrical boundary seems to support the idea of low segregation to grain boundaries with low Miller indices, as the orientations of both planes forming the asymmetrical boundary are inclined only 4° to the {001} and {011} low index planes.