MSE Thesis Defense: “Grain Boundary Structural Responses to Dislocation Loop Absorption”

This talk aims to describe GB responses to absorption of dislocation loops, as part of increasing understanding of component phenomena of radiation damage in materials. The context of radiation damage in materials and the broader importance of understanding related material behavior are summarized, as well as some background on grain boundary structure and defects, and approaches are introduced that will be used throughout the defense. Initially, the discussion presents cases of a Sigma-5 (210)[001] symmetric tilt grain boundary in bcc-Fe responding to absorption of different sizes of interstitial and vacancy loops, which exhibit both a DSC-disconnection reaction and some extent of a state change response concurrently, with extent of each depending on the size and character of the inbound loop. The next case presented details state changes observed in a Sigma-5 (012)[100] STGB in (bcc) Mo after absorption of interstitial loops. The presentation then explores disconnection reaction response to interstitial loop absorption in two Sigma-13 STGBs in Mo. Comparisons and contrasts are drawn between the initial Fe case, which exhibits multiple concurrent response types, and the Mo cases, which each present a single type of response. My defense then presents an approach to characterize defect absorptions by GBs in experimental settings by linking atomistic descriptions of absorption phenomena with experimental Nye tensor measurement changes. Finally, the talk presents overarching conclusions from all of the work discussed, in the hope that understanding these cases of single-loop absorptions and resulting GB responses will then provide more detailed understanding of GB evolution (and factors affecting it) as more defects are absorbed.