DEPENDENCE OF RADIATION-INDUCED SEGREGATION ON DOSE, TEMPERATURE AND ALLOY COMPOSITION IN AUSTENITIC ALLOYS

Radiation-induced segregation (RIS) of austenitic stainless steels was investigated using proton irradiation. Dose and temperature dependence of RIS was determined by irradiation of an Fe-20Cr-24Ni alloy over a range of doses and temperatures. Four additional alloys were included to create three alloy series of either constant Ni or constant Cr to identify bulk composition effects on RIS. Measurements of grain boundary composition were made using Auger electron spectroscopy of grain boundary facets exposed in situ. Results showed that over the dose range 0.1 to 3 dpa grain boundary Ni increased and Cr decreased sharply below 1 dpa and achieved near-saturation between 1 and 3 dpa. Segregation increased from 200 to 500 degrees C, and it did not appear to have saturated by 500 degrees C. For a constant bulk Ni content and for increasing bulk Cr content, grain boundary Cr increases and Ni decreases. For constant bulk Cr content and increasing Ni, grain boundary Cr decreased and Ni increased. Dose and temperature dependence agreed well with Perks' model in trends but not in magnitudes, as did the alloy dependence for the case of fixed bulk Cr and varying Ni content. The dependence of grain boundary Ni on bulk Cr/Ni was opposite that predicted by Perks' model considering only the inverse Kirkendall mechanism. Agreement between measured and model results was achieved by accounting for the composition dependence of the atom-vacancy exchange frequency and the correlation coefficient for diffusion.