At relatively high temperature (T>1020 K = 0.6 Tm), the deformation of a perfect Σ=9(122) symmetrical grain boundary (GB) induced large changes in the initial structure. The structural unit model was used to describe the structure of elementaryΣ=9 DSC dislocations cores, produced at low strain, and higher tilt angle coincidence GB's, produced at large strain . It was shown that the prediction of the GB structural evolution was not so straightforward and that the mixing of structural units depended on the deformation conditions.