Triple ion beam studies of radiation damage in 9Cr-2WVTa ferritic martensitic steel for a high power spallation neutron source

To simulate radiation damage under a future Spallation Neutron Source (SNS) environment, irradiation experiments were conducted on a candidate 9Cr-2WVTa ferritic/martensitic steel using the Triple Ion Facility (TIF) at ORNL. Irradiation was conducted in single, dual and triple ion beam modes using 3.5 MeV Fe++, 360 keV He+, and 180 keV H+ at 80 degrees C, 200 degrees C and 350 degrees C. These irradiations produced various defects comprising black dots, dislocation loops, line dislocations, and gas bubbles, which led to hardening. The largest increase in hardness, over 63%, was observed after 50 dpa for triple beam irradiation conditions, revealing that both He and H are augmenting the hardening. Hardness increased less than 30%, after 30 dpa at 200 degrees C by triple beams, compatible with neutron irradiation data from previous work which showed about a 30% increase in yield strength after 27.2 dpa at 365 degrees C. However, the very large concentrations of gas bubbles in the matrix and on lath and grain boundaries after these simulated SNS irradiations make predictions of fracture behavior from fission reactor irradiations to spallation target conditions inadvisable. (C) 1999 Elsevier Science B.V. All rights reserved.