Experimental Determination of Dislocation Core Structures by HRTEM

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Abstract : The overarching scientific goal of this study is to use state-of-the-art TEM techniques to experimentally characterize dislocation core structures in metals and alloys at the atomic scale. The past year has involved the culmination of efforts on intermetallic alloys and pure fcc metals and the development of new techniques for the study of bcc metals and alloys. Our work on (Ni, Fe)3 Ge indicated that changes in mechanical behavior associated with Fe additions are related to variations in dislocation core geometry and its effect on dislocation mobility. These findings have both motivated and been found to be in agreement with first principles based calculations of dislocation core structures in these alloys. In a related study, our weak-beam TEM and HREM experimental observations of dislocation core structures in fcc gold and iridium have been shown to be in excellent agreement with theoretical predictions for these metals. More recent efforts have focused on developing the techniques for characterizing dislocation core structures in bcc metals. Direct HREM observations of dislocation cores and the derivation of localized electron structure data from electron energy loss spectra (EELS) measurements are long term goals, and preliminary steps toward these challenging tasks are underway.