Wang, M. Bieler, T.R. Compton, C. Kang, D. JACoW Geneva, Switzerland 978-3-95450-191-5 10.18429/JACoW-SRF2017-THPB027 English 792-796 THPB027 ion cavity niobium electron SRF Contribution to a conference proceedings 2018 2018-01 https://doi.org/10.18429/JACoW-SRF2017-THPB027 http://jacow.org/srf2017/papers/thpb027.pdf Although the quality factor of niobium cavities has improved, performance variability arises from microstructural defects such as dislocations and grain boundaries that can trap magnetic flux, block heat transfer, and perturb superconducting currents. Microstructural defect evolution is compared in four samples extracted from a 2.8 mm thick large-grain niobium slice, with tensile axes chosen to generate desired dislocation structures during deformation. The four samples are 1) as-extracted, 2) extracted and annealed, 3) extracted and then deformed to 40% strain, and 4) extracted, annealed at 800 °C 2 hours, and deformed to 40% strain. Electron Channeling Contrast Imaging (ECCI) was performed on all samples to characterize initial dislocation density, dislocation structure evolution due to annealing and deformation, and related to the mechanical behavior observed in stress-strain curves. The orientation evolution and geometrically necessary dislocation (GND) density were characterized with electron backscattered diffraction (EBSD) maps. Fundamental understanding of dislocation evolution in niobium is necessary to develop models for computational cavity design.