Influence of dual beam nickel and helium irradiation on the microstructure of a 304L austenitic stainless steel

In-situ irradiation experiments on a commercial 304L austenitic stainless steel were conducted in the JANNuS platform (CSNSM-Orsay) under single beam conditions (500 keV Ni+ ions with a flux of 5.5×1010 ions.cm-2.s-1 and a dose rate of 4×10-4 dpa.s-1) as well as dual beam conditions (500 keV Ni+ ions with a flux of 5.5×1010 ions.cm-2.s-1 and a dose rate of 10-4 dpa.s-1 and 20 keV He+) up to 2 dpa with a helium appm/dpa ratio of 35 appm/dpa and 750 appm/dpa at 500°C and 400°C. In-situ TEM observations during single beam irradiation suggest no mobility of visible clusters. As expected, Frank loop density and size were, respectively, much higher and much lower at 400°C relative to 500°C Helium was observed to have no effect on the evolution of the microstructure at 500°C with a helium appm/ dpa ratio of 35 appm/dpa. However, helium implantation with a helium appm/ dpa ratio of 750 appm/dpa led to a small decrease in the Frank loop density together with a small increase in the cavity density at 500°C.