Micromechanical testing of oxidized grain boundaries

Stress Corrosion Cracking (SCC) of Alloy 600 (A600) in Pressurized Water Reactors (PWRs) is known to be one of the most expensive and challenging phenomena in the nuclear industry. SCC is difficult to observe, investigate and predict and often it occurs although no obvious visual signs of corrosion are present. Over the last decades, great research efforts have been made to understand SCC of A600 under PWR conditions and many mechanisms based on different theories have been proposed to explain crack initiation and propagation.

Although A600 has been successfully demonstrated to oxidize and fail internally along grain boundaries under PWR primary water conditions, experimental evidence capable of explaining the failure mechanism and its link to microstructure is still insufficient. Micromechanical testing of individual grain boundaries, oxidized in simulated PWR primary coolant, now provides a novel tool for studying fracture dynamics (e.g. brittle failure, plastic deformation etc.) of individual (internally) oxidized GBs. This is where I come into play. In my project I make use of a novel approach to fabricate and micromechanically test micron-sized cantilevers. With this new, exciting approach I am able to obtain information about elastic moduli, yield stress and fracture toughness of tested GBs.

Concomitant  (S)TEM characterisations of the same GBs, enable me to correlate the measured mechanical response to the GBs’ specific microstructure (e.g. carbides along the GBs) and/or degree of oxidation. After acquiring a full experimental data set (e.g. Nanoindentation, 3D FIB slicing, analytical (S)TEM etc.) I am also employing crystal plasticity finite element modelling to fully reconstruct my cantilevers and to model my fracture tests. This includes the simulation of plastic deformation, induced during the micromechanical testing. Aim of my project will be to add unprecedented new insights to the study of stress corrosion cracking.