Critical assessment of low-fluence irradiation creep mechanisms

A climb-controlled guide (CCG) creep model, which has been used to successfully rationalize low-fluence, light-ion irradiation creep data in pure nickel, accounted for low-fluence irradiation creep rates and loop growth rates in Type 316 stainless steel. The model also predicted a weak stress dependence and a weak temperature dependence in agreement with typical observations. Both light-ion and neutron irradiation creep measurements and microstructural observations at low fluences were examined and compared with predictions of the CCG model. Calculated creep rates compared to measured creep rates demonstrated that dislocation glide was the dominant mode of deformation during low-fluence creep when interstitial loops were small. When the interstitial loop radius approached one half the average dislocation glide distance, the dislocation glide contribution was small. The stress-induced preferred absorption (SIPA) creep mechanism contributed an increasing fraction of the total deformation as the loop radius increased and became dominant at fluences greater than 1 displacement per atom (dpa). The CCG creep model assumes that glissile network dislocations intersect the small dislocation loop glide barriers, climb into a favorable orientation, and annihilate the loop through a Burgers vector reaction. Dislocation climb controls the rate of loop annihilation that allows dislocation glide between loop barriers. The creep rate is determined by a balance between irradiation-enhanced dislocation climb and interstitial loop growth. 20 references, 13 figures, 2 tables