Dislocation analysis of a complex sub-grain boundary in UO₂ ceramic using accurate electron channelling contrast imaging in a scanning electron microscope

In this work, accurate electron channelling contrast imaging (A-ECCI) assisted by high resolution selected area channelling patterns (HR-SACP) was used to characterize the structure of a complex low sub-grain boundary in a creep deformed uranium dioxide (UO₂) ceramic. The dislocations were characterized using TEM-style g.b = 0 and g.b x u = 0 contrast criteria. Misorientations across the boundary were measured using HR-SACPs with 0.04 degrees precision and high accuracy EBSD. The boundary was determined to be asymmetric and mixed in nature, composed of two distinct regions with different dislocation morphologies and a misorientation below 0.5 degrees. The A-ECCI, HR-SACP, and HR-EBSD results are consistent, confirming A-ECCI as a powerful tool for characterizing even complex dislocations structures using scanning electron microscopy. This is particularly true for UO₂, since this material is very difficult to thin, which makes TEM examination of sub-boundaries over the scale of several micrometers difficult. Furthermore, in this study, the change in dislocations arrangement along the breath of the complex low angle sub-grain boundary is related to the misorientation across the boundary. (authors)