THE INFLUENCE OF HE DPA RATIO AND DISPLACEMENT RATE ON MICROSTRUCTURAL EVOLUTION - A COMPARISON OF THEORY AND EXPERIMENT

A kinetic model was developed to investigate the influence of the disp lacement rate and helium generation rate on microstructural evolution in austenitic stainless steels. The model integrates the rate equation s describing the evolution of point defects, small point defect cluste rs, helium-vacancy clusters. and the larger cavity size distribution t hat is responsible for observable swelling. Cavity (bubble) nucleation is accounted for by the helium-vacancy cluster evolution, while void formation occurs when bubbles grow beyond a critical size in the large r cavity distribution. A series of ion irradiation experiments were us ed to both calibrate the model and to provide a comparison between mod el predictions and experimental observations. The experiments involved single and dual-beam irradiations of solution annealed AISI-316 stain less steel at 873 K. The displacement rates were in the range of 2 X 1 0(-3) to 1 X 10(-2) dpa/s and the helium-to-dpa ratios were in the ran ge of 0 to 50 appm He/dpa. The maximum displacement dose was 25 dpa. T he experiments revealed a significant effect of helium on both the dis Location structure and the cavity distribution. The model predictions of helium effects over a broad range of He/dpa ratios and displacement rates were consistent with experimental observations.