Irradiation-produced defects in austenitic stainless steel

Abstract

The microstructure of annealed AISI Type 304 and type 316 stainless steels has been characterized by transmission electron microscopy as a function of fast reactor irradiation at fluence levels from 4×1021 to 7×1022 n per sq cm (E>0.1 mev) and at irradiation temperatures from 370° to 700°C. Several irradiation produced defect types where found: voids, Frank faulted loops, perfect loops, dislocation networks, and precipitates. Void number density obeys a power law relationship to fluence, wherein the exponent increases with increasing temperature from 0.8 to 1.4 over the irradiation temperatures investigated. The void size is nearly independent of fluence and increases with increasing temperature. The upper limit irradiation temperature for void formation is about 650° to 700°C. The density and size of Frank faulted loops followed trends similar to those found for voids to temperatures of ∼550°C where unfaulted loops, perfect loops, and dislocation networks coexist. These experimental results do not confirm predictions of recently acvanced models of void formation. The major deficiency of these models appears to be the nucleation rate. Accordingly, empirical nucleation rates were used to formulate a diffusion-controlled void growth model. This model was found to closely describe experimentally determined void growth kinetics.