| dc.description.abstract | High-energy particles introduce significant damage to nuclear structural materials and eventually lead to the failure of the materials. Austenitic stainless steels, as a widely used structural material in current nuclear reactors, are face-centered cubic (FCC) metals with very low stacking fault energy (SFE) that are known to be very vulnerable to irradiation damage. Therefore, it is critical to understand the damage mechanisms and to improve the irradiation resistance of those materials. To achieve the goal, both mechanical properties and irradiation response of nanostructured Ag and Au, which are typical FCC metals with low SFE, are investigated.
Mechanical properties. Ag/Fe multilayers with individual layer thicknesses (h) varying from 1 to 200 nm have been fabricated. The microstructure and mechanical strength of the multilayers have been studied. Comparison of mechanical strength of several Ag based multilayers reveals that this drastic difference may arise from chemical stress due to the difference in stacking fault energy of the layer constituents.
Irradiation response. By using in situ irradiation technique in a transmission electron microscope, it has been shown that NT Ag has significantly improved irradiation tolerance comparing with its coarse-grained counterpart. The surprising resilience of TBs in response to radiation has been revealed. Besides, defect distribution shows a clear dependence on twin thickness. Moreover, irradiation tolerance of NT Ag can be further improved by mixing merely 1 at% of Fe solute atoms into Ag matrix. Similar to NT Ag, NP Au also exhibits the improved irradiation tolerance as compared to coarse-grained, fully dense Au. In situ studies show that nanopores can absorb and eliminate a large number of irradiation-induced defect clusters. Besides, it has been shown that both defect density and nanopores evolve with radiation temperature. The sink strength of nanopores as a function of temperature is estimated. Moreover, NP Au exhibits significantly enhanced swelling resistance compared to coarse-grained Au. Potential mechanisms for temperature dependent radiation resistance of NP metals are discussed.
This dissertation serves as a fundamental understanding of both mechanical properties and irradiation response in FCC metals with low SFE and assists the design of advanced nanostructured materials with enhanced radiation tolerance. | en |
