Temperature dependence of the dislocation microstructure of PCA austenitic stainless steel irradiated in ORR spectrally-tailored experiments

Specimens of solution-annealed (SA) and 25% cold-worked (CW) PCA austenitic stainless steel were irradiated in ORR in spectrally-tailored experiments specially designed to produce fusion-relevant He/dpa ratios (12-18 appm He/dpa). SA and CW PCA were irradiated at 330 and 400C to 13 dpa while only CW PCA was irradiated at 60, 200, 330 and 400C to 7.4 dpa. While cavities and fine MC precipitates were only detectable at 330 and 400C, dislocations were a major component of the radiation-induced microstructure at 60-400C. The mixtures of black loops, larger Frank loops, and network that comprised the total dislocation structure were very dependent on irradiation temperature. Both SA and CW PCA contained Frank loops and network dislocations at 330 and 400C. Frank loop concentrations were maximum at 330C and dislocation evolution with dose was most evident at 400C. At 60 and 200C, the microstructure was dominated by very dense dispersions of (1/3 nm diam.) black loops. Some Frank loops were observed at 200C, but almost none were found at 60C. Surprisingly, there was significant radiation-induced recovery of the as-cold-worked dislocation network in CW PCA at all irradiation temperatures. There appears to be a distinguishable transition in the nature of the radiation-induced microstructure between 200 and 330C