2 Relationship of Grain Boundary Structure and Mechanical Properties of Inconel 690 By

Stress corrosion cracking (SCC), failure due to environmentally assisted crack nucleation and propagation, is an important metallurgical problem with impact on current and future designs of ship structural components and nuclear reactors. SCC occurs in the presence of tensile stress, corrosive environment, and a material with susceptibility. The initiation of SCC is difficult to detect and control due to the highly localized nature of chemical and mechanical conditions. As a result, its inhibition has been a particularly challenging problem. SCC mechanism is dependent on the microstructure, particularly the grain boundaries, for a given alloy composition. Therefore, inhibition could be sought from an improved fundamental understanding of the structural and mechanical characteristics at the material’s grain boundaries. This thesis investigated the relationship between the structural nature and the nanoscale mechanical properties on and near the grain boundaries to identify their role in the resistance to stress corrosion cracking. Inconel 690, an austenitic Ni-alloy, was chosen as the material of interest for its relevance in current applications in the nuclear energy technology. An integrated approach to probe the structural, mechanical and chemical information at the nanoscal