On Σ9 grain boundary plane orientation

Past measurements of the orientation of the Sigma 9 grain boundary plane have consistently shown that it adopts a tilt orientation. However, in different circumstances, a wide range of symmetric and asymmetric tilt boundaries are observed. Here, a stereological interpretation of electron-backscatter diffraction data was used to measure the orientation of the Sigma 9 grain boundary plane in Fe-30Ni. The grain boundary plane orientation was found to be influenced by the types of boundaries meeting the Sigma 9 at triple points. Sigma 9 boundaries attached to random high angle boundaries showed a nearly continuous range of symmetric and asymmetric tilt boundaries. Sigma 9 boundaries attached to Sigma 3 boundaries selectively adopted a range of lower energy grain boundaries with grain boundary normals between (001) and (1 (1) over bar1) orientations. As the coherency of the attached Sigma 3 boundaries increased, the grain boundary plane orientation maximum was found at the (1 (1) over bar4)//(1 (1) over bar4) symmetric tilt orientation, thought to be minimum energy for this disorientation. The distribution of Sigma 9 grain boundary plane orientations depends on the fraction of Sigma 3 boundaries and how close they are to the coherent twin orientation.