A critical test of the classical rate theory for void swelling

Swelling and radiation-induced segregation in austentic alloys

“…3. Consistent with the work of Okita on the effect of displacement rate [16], the effect of bulk nickel on swelling occurs in the void density and not the void size. Fig.…”

“…Because a difference in bias for point defects between dislocations and cavities is required for swelling to occur, segregation may alter the net bias and thus alter the swelling. Since measurements have shown that swelling in austenitic stainless steels ultimately reaches a terminal rate of 1%/dpa, any effect of segregation on swelling during void growth is likely to occur during the transient phase of void swelling, consistent with the work of Okita [16].…”

“…The increase in critical radius corresponded with a change in dislocation microstructure, with higher nickel concentration leading to a larger concentration of faulted loops, which are weaker sinks for vacancies than dislocation networks. Okita and Wolfer [16], examining an Fe-15Cr-16Ni ternary alloy irradiated in FFTF, recently showed that the displacement rate dependence of void swelling occurs due to changes in the void density rather than the void size. The dislocation density also increased at lower displacement rate, changing in a manner similar to the void density.…”

The Dislocation Bias

“…We can determine its value by inserting equation (15) into equation (13) and integrating it. The result is…”

“…It now demands a larger empirical bias on the order of 0.1 to 0.2 to explain the void swelling rate of 1%/dpa measured in austenitic stainless steels, and this larger bias agrees now much better with the theoretically derived values. Indeed, a careful analysis of void swelling data [13] obtained for pure ternary austenitic steels, lacking any precipitates and impurities, and comparing the data with theoretical predictions of void swelling implies bias values between 0.25 and 0.40 for network dislocations and between 0.40 and 0.55 for prismatic dislocation loops.…”