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195281 https://hdl.handle.net/2286/R.2.N.195281 http://rightsstatements.org/vocab/InC/1.0/ All Rights Reserved 2024 2026-08-01T16:04:42 105 pages Doctoral Dissertation Academic theses Text eng Sharma, Saurabh Solanki, Kiran N. Alford, Terry Ankit, Kumar Darling, Kris A. Arizona State University Partial requirement for: Ph.D., Arizona State University, 2024 Field of study: Materials Science and Engineering Nanocrystalline (NC) alloys with stable microstructures have attracted significant interest from researchers due to their exceptional thermo-mechanical properties. While the increased volume fraction of grain boundaries enhances mechanical strength, it also accelerates diffusion, leading to rapid oxidation. In coarse-grain alloys, oxide layer formation during oxidation is influenced by factors such as solute concentration, distribution, and the protective nature of oxides. However, there is a limited understanding of how these factors influence the formation of an oxide layer in stable NC alloys. Thus, this dissertation systematically studies the oxidation behavior in microstructurally stable NC Cu-Ta alloys, i.e., Cu-3at.%Ta and Cu-10at.%Ta alloys. Towards this, thermogravimetric and oxide scale cross-sectional analyses were performed to investigate underlying mechanisms of oxidation. Dynamic and isothermal oxidation examination followed by TEM analysis indicates that the Ta concentration plays a key role in controlling the mechanisms where NC Cu-3at.%Ta showed a higher oxidation resistance due to the absence of large Ta precipitates. A third-element approach was also employed to further enhance the oxidation performance of these alloys by adding varying concentrations of Cr to the Cu-3at.%Ta alloy. The ternary alloy was then compositionally optimized to achieve improved oxidation resistance and significant mechanical performance. The optimized Cu-Ta-Cr alloy achieved this through a unique blend of microstructural features, including the formation of Cr-Ta precipitates along with Ta nanoclusters. TEM analysis indicated that these precipitates could form oxide particles, which limits the diffusion of Cu during oxidation. To further analyze the role of these precipitates on the material's performance, both compression creep and humidity-incorporated oxidation experiments were conducted to simulate actual application environments. The optimized Cu-Ta-Cr alloy demonstrated comparable creep behavior to conventional Cu-based alloys used in structural applications like high heat flux situations. Experiments conducted in a humid atmosphere demonstrated higher oxidation in the Cu-Ta-Cr alloy, as evidenced by the formation of oxide whiskers, which were limited in dry air. Nevertheless, the weight gain in the Cu-Ta-Cr alloy was still lower than that of NC Cu-3at.%Ta. Overall, this work advances the current understanding of oxidation behavior in stable NC alloys and aids in developing design strategies for engineering oxidation-resistant materials while maintaining thermo-mechanical properties. Materials Science Creep Humidity based oxidation Mechanical Behavior Nanocrystalline alloys Oxidation Investigating Oxidation Behavior of Stable Nanocrystalline Alloys