Microstructural response of titanium-modified austenitic stainless steels to neutron exposure of 70 dpa in FFTF/MOTA

JPCA, a titanium-modified austenitic stainless steel, in solution-annealed or cold-worked condition and a compositionally modified JPCA in solution-annealed condition were examined by transmission electron microscopy following irradiation in FFTF/MOTA to an exposure level of up to about 70 dpa at 390 to 600°C. At lower temperatures, all the materials developed qualitatively similar cavity-, dislocation- and precipitate-microstructures. The lower-temperature swelling peak, which appeared at near 410°C, was more efficiently suppressed by phosphorus addition than cold-working. Irradiation at or above 520°C produced substantially large swelling in solution-annealed JPCA. The cavities contributed to this higher-temperature swelling developed in association with M₆C-type precipitates. Neither cavities other than very small helium bubbles nor massive particles of M₆C-type precipitates were observed in cold-worked and phosphorus-modified materials, in which MC-type precipitates developed at very high concentration. The effect of pre-irradiation microstructure and compositional modification on the behavior of these precipitates is discussed.