Plastic flow and microstructure evolution in niobium at elevated temperatures

dc.contributor.advisorTaleff, Eric M.
dc.contributor.committeeMemberKovar, Desiderio
dc.contributor.committeeMemberMangolini, Filippo
dc.contributor.committeeMemberSeepersad, Carolyn
dc.creatorBrady, Emily Ann Dukes
dc.date.accessioned2022-05-13T19:17:59Z
dc.date.available2022-05-13T19:17:59Z
dc.date.created2021-12
dc.date.issued2021-12-09
dc.date.submittedDecember 2021
dc.date.updated2022-05-13T19:18:00Z
dc.description.abstractPlastic flow and microstructure evolution are investigated at elevated temperatures in two unalloyed niobium sheet materials, Type 1 and Type 2 as designated in ASTM B393-18. Tensile tests are conducted at temperatures from 1473 to 1823 K (1200 to 1550°C) at constant true strain rates of 10⁻³ and 10⁻⁴ s⁻¹. Deformation microstructures are characterized using backscatter electron (BSE) imaging, electron backscatter diffraction (EBSD), and high-resolution EBSD (HR-EBSD). The mechanical behaviors of the Type 1 and Type 2 niobium materials are compared to relevant data from the literature. Elevated temperature deformation in both niobium materials is dominated by the five-power creep mechanism and the associated development of subgrains. The higher impurity content of the Type 2 niobium led to: 1. greater strength, 2. delayed recrystallization, 3. slower grain growth, 4. inhomogeneous microstructures, and 5. slower recovery which resulted in finer and less distinct subgrains compared to the Type 1 niobium. The smaller subgrain size of the Type 2 niobium produces, through the five-power creep mechanism, a higher strength at elevated temperature compared to the Type 1 niobium. This is the first mechanistic explanation supported by direct microstructural data for how impurity content affects strength in refractory metals. HR-EBSD analysis is performed on the deformed Type 2 niobium material by developing new techniques to: 1. utilize data from a new EBSD instrument, 2. expand the capabilities of the OpenXY open-source cross-correlation software, and 3. enable cross correlation calculations spanning the breadth of heavily deformed grains. This is the first successful implementation of these techniques.
dc.description.departmentMaterials Science and Engineering
dc.format.mimetypeapplication/pdf
dc.identifier.urihttps://hdl.handle.net/2152/114155
dc.identifier.urihttp://dx.doi.org/10.26153/tsw/41058
dc.language.isoen
dc.subjectNiobium
dc.subjectHigh-temperature deformation
dc.subjectGrain growth
dc.subjectCreep
dc.subjectSubgrains
dc.subjectElectron backscatter diffraction (EBSD)
dc.subjectElastic modulus
dc.subjectHigh resolution electron backscatter diffraction
dc.titlePlastic flow and microstructure evolution in niobium at elevated temperatures
dc.typeThesis
dc.type.materialtext
thesis.degree.departmentMaterials Science and Engineering
thesis.degree.disciplineMaterials Science and Engineering
thesis.degree.grantorThe University of Texas at Austin
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy
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