Measurement of Compositional Profile of ID Facets by FEG-AES and its Relevance to IDSCC of Alloy 182 in a Simulated BWR Environment

摘要

Environmentally Assisted Cracking (EAC) of weld metal, Alloy 182 is currently great concern in such components as head penetration, control rod drive housing and core shroud supports in nuclear power plants. The microstructure of Alloy 182 is dendritic and the most susceptible crack plane is known to be parallel to the direction of the dendrites. Electron Backscattered Diffraction Patterns (EBSP) analyzed the distribution of the grain boundary character. A compositional profile of the dendritic grain boundary of sensitized Alloy 182 was performed by Field Emission Gun-Auger Electron Spectroscopy (FEG-AES) on the InterDendritic (ID) facets. The dendrites were generated by slow strain rate tests in high vacuum with the tensile stage attached to the AES. For the sample with hydrogen charging, data showed a significant variation of Chromium and Phosphorus concentration on the ID facets. Chromium was depleted down to 2% on some facets and phosphorus was enriched to several % on some facets. The data was evaluated statistically. The FEG-AES technique has an advantage over ATEM that large amounts of data can be obtained. Hundred of data points were obtained by this technique. Stress Corrosion Cracking (SCC) crack growth data obtained in a simulated Boiling Water Reactor (BWR)'s water environment will be discussed along with those compositional profiles on ID facets.