AbstractCreep responses of austenitic stainless steels to cyclic 10 MeV deuteron irradiation have been examined, for solution-annealed (SA) or 20% cold-worked (CW) 316 stainless steel (SS) and Fe25Ni15Cr alloy. After the strain rate reached a steady state under a long-term continuous irradiation, the irradiation mode was switched to square waveforms (pulse width τP = 10 ms–1000 s). Anomalous large creep enhancement due to the cyclic irradiation was observed at a particular pulse width range around τP = 100 s, even at a low damage rate of 2.0 × 10−7 dpa s−1, whereas the specimen gave zero or negative strain changes with respect to the steady state level at τP < 1 s or τP > 200 s. Consequently, the pulse width dependence of strain change had a resonant feature with a peak around τP = 100 s. The SA-316 SS and SA- and CW-Fe25Ni15Cr alloys exhibited strain increments of about 10−4 for 10−3 dpa, which were larger by one to two orders of magnitude than the steady state creep. The mechanism of the large creep is ascribed to pulse-induced point defect enrichment, by the aid of a rate theory. It was thus demonstrated that first-wall materials in a plasma operation of about 102 s may suffer from unexpected transient creep and that the dynamic aspects for damaging effects on the first-wall materials should be taken into account, especially for fusion devices to be operated at low temperatures such as ITER.
Prediction of long-term creep curves