0000000000345303
AUTHOR
Marc Foucault
Optical modeling of nickel-base alloys oxidized in pressurized water reactor
International audience; The knowledge of the aging process involved in the primary water of pressurized water reactor entails investigating a mixed growth mechanism in the corrosion of nickel-base alloys. A mixed growth induces an anionic inner oxide and a cationic diffusion parallel to a dissolution-precipitation process forms the outer zone. The in situ monitoring of the oxidation kinetics requires the modeling of the oxide layer stratification with the full knowledge of the optical constants related to each component. Here, we report the dielectric constants of the alloys 600 and 690 measured by spectroscopic ellipsometry and fitted to a Drude-Lorentz model. A robust optical stratificati…
Early-stage detection of surface stress corrosion cracking at the subgranular level
The strain field at the interface between an alloy and its oxide layer has been mapped using nanopatterned gauges resistant to the environment of the primary nuclear medium. It was found that oxidation has decreased the alloy ductility, thereby enabling some grain boundary opening to be detectable from 1.8 % strain. It is shown that statistics of extreme rare events of hotspots quantify the occurrence of the local opening of intergranular cracks, and thereby the ageing process.
A Methodology to Deduce the Microstructural Spatial Deformation of Polycrystalline Structures: Application to the Alloy 600
Studying the corrosion of the alloy 600, under water pressure, is of high importance to understand the ageing process of pressurized water reactors. Today, the impact of the oxide growth on the mechanical properties of nickel alloys is a challenge. The surface analysis and the quantification of the local deformation are key factors to deduce the surface damage of the substrate produced by corrosion. Here, we introduce a new methodology to determine the deformation distribution of the alloy 600 by using polycrystalline samples. The method is based on nanopads disposed on the surface samples, which allow a mapping, at the microscopic scale, of the spatial deformation. We applied to the sample…
Strain mapping near a triple junction in strained Ni-based alloy using EBSD and biaxial nanogauges
A key element for analyzing the crack initiation in strained polycrystalline alloys is the local quantification of the surface strain distribution according to the grain texture. Using electron backscattered diffraction, the local microstructure was determined to both localize a triple junction and deduce the local Schmid factors. Kernel average misorientation (KAM) was also used to map the areas of defect concentration. The maximum principal strain and the in-plane shear strain were quantified using the biaxial nanogauge. Distortions of the array of nanodots used as spot markers were analyzed near the triple junction. The crystallographic orientation and the surface strain were then invest…