Microstructural stability of nanostructured alloys under harsh environments such as high temperatures and high dose irradiation is a primary concern in the deployment of those materials for engineering applications. This thesis work explores several pathways to stabilize nanostructures in Cu-based ternary alloy systems, which contain a very small fraction of refractory alloying element (W) that is highly immiscible with Cu. Three systems with distinct interaction energies have been investigated. 1) In the Cu-Nb-W system, where Nb is moderately immiscible with Cu but is miscible with W, very stable Nb-rich core/W-rich shell nanoprecipitates form upon annealing, as a result of the competition between thermodynamics and kinetics of Nb and W in Cu. When samples are first subjected to room temperature irradiation, however, W-rich core/Nb-rich shell nanoprecipitates form instead. These nanoprecipitates display even stronger resistance to thermal coarsening, which is rationalized by the very high trapping efficiency of ramified W cores for Nb atoms. 2) In the Cu-Ag-W system, where Ag is moderately immiscible with Cu and is highly immiscible with W, compositional patterning, as a steady state of the system under irradiation, can be extended to much higher temperatures by first using room temperature irradiation to introduce W nanoprecipitates, which then serve as sinks for point defects during elevated temperature irradiation. 3) In the Cu-Ni-W system, where Ni is miscible with Cu with a small positive heat of mixing but tends to form compound with W, irradiation-induced W nanoprecipitates force the Ni atoms out of solution during annealing, forming Nb-W compound, and the system evolves towards the same steady state during room temperature irradiation, regardless of the initial state.The work contains both experimental and computational studies.
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Nanoscale self-organization in irradiated ternary alloys
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