Microstructural evolution during initial stages of static recovery and recrystallization: new insights from in-situ heating experiments combined with electron backscatter diffraction analysis

We present in-situ observations, performed using electron backscatter diffraction, of static recovery and recrystallization processes occurring in a plastically deformed geological material, namely rocksalt. Static heating experiments, carried out in a scanning electron microscope at temperatures of up to 450 °C, allowed direct detailed observations of grain boundary migration between substructured grains in deformed polycrystalline samples. Contrary to expectations, crystallographic orientation maps reveal that behind slowly migrating grain boundaries new subgrain boundaries form while pre-existing subgrain boundaries are sometimes inherited. Moreover, the crystallographic character, especially the preferred orientation of misorientation axes of the new substructures reflects the character of the previous deformation history. These results imply that substructural features, such as subgrain misorientation distributions, may be relatively robust indicators of deformation mechanisms and conditions, even in tectonites that have undergone late, static recrystallization. In addition, our observations suggest that the process of static grain boundary migration does not necessarily reset earlier deformation microstructures as commonly assumed. The kinematic observations of boundary migrations are inconsistent with simple models in which migration is achieved by single atoms jumping across the boundary.