Effect of Ni and Cr concentration on grain boundary segregation in Fe-Cr-Ni alloys

Fe-Cr-Ni austenitic alloys were irradiated to investigate the dependence of radiation induced grain boundary segregation on the initial composition of alloying elements. Electron irradiations were performed at grain boundary by using HVEM with 1000 keV accelerating voltage. The irradiation temperature was 723 K and the dose was up to 7 dpa. Measurements of grain boundary composition were made using 200 keV TEM with EDS analysis device. Typical grain boundary segregation, such as Ni enrichment and Cr depletion, was recognized in all specimens. The amounts of segregation varied with the contents of alloying elements. For constant bulk Cr (15 wt% Cr) concentration and for increasing bulk Ni concentration, from 15 to 40 wt%, the highest amount of Ni segregation was observed in the range of 25 to 30 wt% Ni specimens, and Cr concentration at grain boundaries was of almost the same level. For constant bulk Ni (20 wt% Ni) content and for increasing bulk Cr content, from 15 to 35 wt%, the amount of Cr segregation at grain boundaries increased with greater Cr bulk content and the amount of Ni segregation was almost the same over the range of 15 to 35 wt% Cr. These tendencies of segregation which depend on the alloying composition were consistent with the computer simulation results of the grain boundary segregation. (orig.)