Thermal and Radiation-induced Segregation in Model Ni-base Alloys

Since Generation IV nuclear energy systems will operate at higher temperatures than current light water reactors, Ni-base alloys are receiving attention as candidate core materials. One aspect of the radiation response of Ni-base alloys to radiation that is not well understood is grain boundary segregation. In this work, three alloys, specifically Ni-18Cr, Ni-18Cr-9Fe, and Ni-18Cr-0.08P were given a series of thermal treatments and quenching to understand the development of thermal non-equilibrium segregation (TNES). Additionally, they were irradiated using 3.2 MeV protons at temperatures from 200 to 500 C to doses up to 1 dpa. Grain boundary segregation was measured with Auger Electron Spectroscopy and Scanning Transmission Electron Microscopy with Energy Dispersive Spectroscopy. Chromium enrichment due to TNES could be caused by interactions between Ni and Cr or by interactions with impurity elements such as B, C, or N. Under irradiation, the addition of iron to Ni-18Cr reduced the grain boundary chromium depletion, while the addition of phosphorous increased the grain boundary chromium depletion.