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Thesis_Aug13_Shakil
Embargoed Access, Embargo ends: 10/13/2027
Thesis
MECHANICAL PROPERTIES OF PURE NIOBIUM AT CRYOGENIC TEMPERATURES
Master of Science (MS), Washington State University
2026
Abstract
Niobium (Nb) is used in superconducting radio frequency cavities where it undergoes millions of stress cycles in its lifetime at cryogenic temperature approaching 4 K. However, fatigue lifecycle of pure Nb at this test condition is scarce and there is a lack of fundamental understanding of deformation mechanisms as well. In this project, the tensile, fatigue, and indentation mechanical response of high purity and commercially pure Nb at cryogenic temperatures was studied. To establish baseline mechanical properties including Young’s modulus, yield strength, and ultimate tensile strength, uniaxial tensile tests were performed at different cryogenic temperatures and room temperatures for both materials. Tension-tension fatigue tests were performed at varying mean stresses (S) and stress amplitudes to develop S-N curves, which represent the number of cycles (N) sustained before failure (N) or materials lifetime under different cyclic stress conditions. The fatigue lifetime for commercially pure Nb was found to be higher than the commercially pure Nb at the same stress level. To identify the failure mechanisms, microstructural analysis was performed on both undeformed surfaces and fracture surfaces of specimens tested under indentation, uniaxial tension, and fatigue loading. For high purity Nb, the fracture surfaces from tensile tests showed signatures of ductile failure at all testing temperatures, including 20 K. In contrast, the fracture surfaces from fatigue tests showed fully brittle failure in both materials. Additionally, nanoindentation tests performed over the temperature range of 298–153 K showed that commercially pure Nb becomes progressively harder as the temperature decreases.
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Details
- Title
- MECHANICAL PROPERTIES OF PURE NIOBIUM AT CRYOGENIC TEMPERATURES
- Creators
- MD SHAKIL MAHMOOD
- Contributors
- Arezoo Zare (Advisor)Jacob Leachman (Committee Member)David Field (Committee Member)Shreyas Balachandran (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- School of Mechanical and Materials Engineering
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Number of pages
- 95
- Identifiers
- 99901418806101842
- Language
- English
- Resource Type
- Thesis