RADIATION-INDUCED SEGREGATION AT GRAIN-BOUNDARY IN AN AUSTENITIC STAINLESS-STEEL UNDER ION IRRADIATION

Chromium depletion near grain boundaries of austenitic stainless steel during irradiation was investigated. Specimens were kept at 1,473 K f or 30 min, and were quenched into the water. Irradiations were done us ing 400 keV He+ ions at 573, 673 and 773 K up to 10 dpa with a dose ra te of 2.4x10(-4) dpa/s. After irradiation, the Cr concentration profil e near the grain boundary was measured using an analytical electron mi croscope with a 1 nm beam diameter. At 573 K, Cr depletion is small, a nd its concentration at the grain boundary decreases to 15.5 mass% at 3dpa from the initial concentration of 18.5 mass%. At 673 and 773 K, C r concentration at the grain boundary rapidly decreases between 0 and 0.2 dpa, and then gradually approaches a constant value, 7.0 mass% at 673 K and 5.0 mass% at 773 K. Two stages are found in radiation induce d segregation (RIS) behavior, one stage in which Cr depletion and Ni e nrichment balance and another in which Fe depletion and Ni enrichment balance. These experimental results were compared with the calculation s based on the vacancy-induced inverse Kirkendall effect. Predicted Cr segregation at 673 and 773 K above 3 dpa agrees with the experimental results. But Cr depletions at low doses which were obtained in the ex periments are much faster than calculated. At 573 K in the experiments , depletion is smaller than calculated up to 10 dpa.