Microstructural changes of ferritic/martensitic steels after irradiation in spallation target environments

Ferritic/martensitic (FM) steels are the one of major classes of materials included in the SINQ Target Irradiation Program performed at the Paul Scherrer Institute. A large matrix of FM steels from various international nuclear materials programs were irradiated at SINQ in a wide range of irradiation dose (5-30 dpa) and temperature (80-600 degrees C). Owing to high energy protons producing helium and hydrogen at high rates (up to 80 appm He and 400 appm H per dpa), the irradiation-induced microstructural and mechanical changes in the FM steels are significantly different from that of fission neutron irradiations. Extensive microstructural characterization of these irradiated FM steels has been conducted by employing transmission electron microscopy, positron annihilation spectroscopy and atom probe tomography analyses. Irradiation-induced microstructural features such as defect clusters/dislocation loops, cavities/helium bubbles and precipitates of alloying-elements and transmutation products have been studied. In this paper the results of the microstructural investigations obtained from the specimens of several FM steels irradiated to 5-20 dpa are reviewed. (c) 2018 Elsevier B.V. All rights reserved.