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Irradiation of metals with energetic particles causes heavy damage effects in microstructure and mechanical properties, which is closely associated with irradiation conditions, presence of impurities, and microstructural features. It has been proposed that the radiation tolerance of a certain material can be enhanced by introducing a high density of interfaces, acting as ‘sinks’ that can frequently involve in attracting, absorbing and annihilating defects. Nanostructured materials with large volume fraction of interfaces, therefore, are assumed to be more radiation tolerant than conventional materials. This thesis focuses on the radiation damage effects in nanostructured Cu via the methods of in-situ TEM (transmission electron microscope) radiation experiments, postirradiation TEM analyses, small-mechanical tests (nanoindentation and micro-pillar compression), and computer simulations (molecular dynamics and phase-field modeling). We design and fabricate nanostructured Cu using direct current (DC) magnetron sputtering deposition technique, a typica physical vapor deposition (PVD) method and a bottom-up way to construct various nanostructured metals. High-density twin boundaries (TBs) and nanovoids (NVs) are introduced into two distinct nanostructured Cu films, including nanovoid-nanotwinned (NVNT) Cu (111) and nanovoid (NV) Cu (110). The in-situ high-energy Kr⁺⁺ (1 MeV) and ex-situ low energy He⁺ (< 200 keV) irradiations are subsequently preformed on the as-deposited Cu samples. On the one hand, the in-situ TEM observations suggest that TBs and NVs can influence the formation, distribution and stability of radiation-induced defects. Meanwhile, the preexisting microstructures also undergo structural change through void shrinkage and twin boundary migration. On the other hand, the ex-situ micro-pillar compression tests reveal that the Heirradiated NV-NT Cu contains less defect clusters but experiences more radiation-induced hardening. The underlying mechanisms of void shrinkage, twin boundary migration, and radiationinduced hardening are fully discussed based on post-irradiation analyses and computer simulations.

<p><a>Aluminum (Al) alloys have been widely used in </a>industry as light-weight structural materials. However, the mechanical strength of the strongest Al alloys is still much lower than most high-strength steels. This thesis aims to investigate the fabrication and mechanical behaviors of nanotwinned high-strength Al alloys and multilayers.</p> <p>Twin boundaries are special grain boundaries with mirror symmetry. Twin boundaries can generate slip discontinuity and block the transmission of dislocations, and serve as dislocation sources to accommodate plasticity. However, twinning in Al is rare due to its high stacking fault energy and low unstable stacking fault energy. In this thesis, we used multiple methods to introduce high-density twins into Al and achieve outstanding mechanical properties and thermal stability. </p> <p>Certain type of solutes can greatly increase the twin density in Al by decreasing the stacking fault energy of Al and retarding the detwinning process. Nanotwinned Al-Ni and Al-Ti binary alloys fabricated by magnetron sputtering show high strength, good deformability, and unique deformation mechanisms. Furthermore, deformation and thermal stability of binary nanotwinned Al alloys can be enhanced by adding a third or fourth solute element. </p> <p>Interfaces can facilitate twin formation in Al as well. High-density twins and stacking faults were introduced into Al by using Al/Ti layer interfaces. Nanotwinned Al/Ti multilayers have ultra-high strength, superb deformability and thermal stability. This thesis provides promising pathways to fabricate Al alloys and composites with high strength and good thermal stability.</p>