UC Berkeley

Structural materials in nuclear applications are subjected to extreme environments including radiation flux, stress, corrosion, and temperature. These environments can induce brittle failures by changing the material microstructures through either introducing new defects or modifying the pre-existing defects. In this thesis, the role of defects’ mechanical stability on the two primary causes of brittle failures, being strain localization and intergranular cracking are studied. A wide range of defect types from 0D to 3D defects – including interstitial atoms, radiation-induced loops, long-range ordered precipitates, voids, and interfaces – are considered. Additionally, the effects of radiation damage on various pre-existing defects in structural materials are studied. The second aspect of the thesis is to expand the capability of in situ SEM small-scale mechanical testing for a wide range of testing geometries and material conditions. Single-crystal microcompression and microtension are developed to assess the plastic deformation of individual grains as a function of defect types. Furthermore, novel bicrystal testing of grain boundaries are developed to measure the grain boundary strength of oxidized and irradiated materials. The key findings of the thesis reveal that the mechanical stability of the defects strongly influence strain localization, slip formation, and microscale plasticity. Furthermore, the stability of intragranular defects reduce the intergranular cracking susceptibility by inhibiting strain localization.