Effects of helium on radiation-induced defect microstructure in austeniticstainless steel

In the construction materials surrounding the spallation neutron source (SN S) mercury target, considerable quantities of transmutation products, parti cularly hydrogen and helium, will be generated due to the exposure to a hig h flux of 1 GeV protons and associated neutrons. In an effort to investigat e the effects of high helium, therefore, bubble formation and defect cluste ring processes in AISI 316 LN austenitic steel were studied as a function o f helium concentration and displacement damage dose with 360 keV He+ and 35 00 keV Fe+ ion beams at 200 degrees C. Helium irradiation was less effectiv e in producing defects such as black dots and dislocation loops than Fe+ io n irradiation at equivalent displacement dose. On the other hand, the forma tion of helium bubbles produced a strong depressive effect on the growth of loops and the evolution of line dislocations. The results indicated that t he effect of helium bubbles was augmented as the bubble number density and size increased with increasing helium beyond 1 atomic percent (at.%). Tn su ch a case, the effect of helium bubbles can be more important than that of radiation-induced defects on the evolution of microstructure and the change in mechanical properties. (C) 2000 Elsevier Science B.V. All rights reserv ed.