First combined electron backscatter diffraction and transmission electron microscopy study of grain boundary structure of deformed quartzite

摘要

The structures of boundaries in a deformed and dynamically recovered and recrystallized quartz polycrystal (mylonite) were characterized by transmission electron microscopy, after the misorientation angles across the same grain boundaries had been analysed using electron backscatter diffraction in a scanning electron microscope. In this new approach, a specific sample area is mapped with electron backscatter diffraction, and the mapped area is then attached to a foil, and by the ion beam thinned for transmission electron microscopy analysis. Dislocations in grain boundaries were recognized as periodic and parallel fringes. The fringes associated with dislocations are observed in boundaries with misorientations less than 9 degrees, whereas such fringes cannot be seen in the boundaries with misorientations larger than 17 degrees. Some boundaries with misorientations between 9 degrees and 17 degrees generally have no structures associated with dislocation. One segment of a boundary with a misorientation of 13.5 degrees has structures associated with dislocations. It is likely that the transition from low-angle to high-angle boundaries occurs at misorientations ranging from approximately 9 degrees to 14 degrees. Change in the grain boundary structure presumably influences the mobility of the boundaries. In the studied deformed quartz vein, a relative dearth of boundaries between misorientation angles of theta = 2 degrees and theta = 15 degrees has previously been reported, and high-angle boundaries form cusps where they intersect low-angle boundaries, suggesting substantial mobility of high-angle boundaries.