Coupling and scale effects: two main issues to begin to understand intergranular stress corrosion cracking in nickel bases alloy.
Résumé
Intergranular stress corrosion cracking (IGSCC) of Nickel based alloys in PWR environment is a coupled phenomenon that involves several factors related to the material (crystallographic orientations and misorientations of the grains, nature in term of lattice structure coincidence factor and orientation of the grain boundaries versus the maximum stress applied, the environment (temperature, pH of the solution, partial pressure of O$2$) and the mechanical loading (effect of the strain path, residual stresses, strain heterogeneities). In this study, we propose a methodology based on a local approach that combined EBSD mapping to characterize the microstructures, DIC technique to determine strain heterogeneity localizations and finite element simulations to estimate local stress states that allow us to evaluate a stress corrosion cracking criterion. We will discuss how this criterion could be related with the depth of the penetration oxide, what modify the intrinsic cohesive energy of the grain boundaries. So, discussion should be open concerning the use of cohesive zone models, with evolution of the open stress regarding the evolution of the nature of the species (oxide or metal) that define the grain boundaries.
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