The effect of alloy composition on radiation-induced segregation in Fe-Cr-Ni alloys

The effect of alloy composition on radiation-induced segregation (RIS) was investigated in austenitic iron-base and nickel-base alloys using proton irradiation. Specifically, RIS was studied by irradiation of Ni-18Cr, Ni-18Cr-9Fe, and Fe-20Cr-9Ni over a dose range of 0 to 1.0 dpa and a temperature range of 200 to 500 degrees C. Grain boundary composition was measured using Auger electron spectroscopy and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy. Measurements from this study along with measurements from Fe-16Cr-24Ni, Fe-20Cr-24Ni, Fe-2rCr-24Ni, and Fe-24Cr-19Ni alloys irradiated with protons confirm that RIS is strongly dependent on the alloy composition. Trends in segregation behavior in Fe-base alloys are consistent with high temperature diffusion measurements, indicating that a vacancy mechanism is the most likely primary driving force for RIS in austenitic steels. The migration energy for Cr is shown to be larger than the migration energy of Fe, Segregation measurements in Ni-base alloys are not consistent with high temperature diffusion measurements, indicating that ordering forces may be significant in the segregation process, Comparison of model calculations to measured RIS data indicate that Fe, Cr, and Ni diffusivities axe composition dependent. This dependence on alloy composition limits the predictive ability of simple models because of the need for separate diffusion parameters for every alloy composition.