Sequential Low Dose Proton Irradiation and Nanomechanical Testing to Understand Mechanical and Microstructural Property Changes in Alloy 709

Alloy 709, a 20Cr25Ni alloy, is an advanced austenitic steel designed for next generation sodium fast reactors. Preliminary studies have shown the potential of Alloy 709 in sodium fast reactors. In this study, Precipitate Treated Alloy 709 specimens are irradiated with 2 MeV H+ at 500 °C from 0.0057 dpa to 1.7 dpa. Electron microscopy characterization techniques are used to understand the effects of radiation on mechanical properties as well as microstructure of Alloy 709. The microstructure did not show formation of voids, amorphization of precipitates, or increase in grain size up to 1.7 dpa. Correspondingly nano-indentation and micro-pillar compression do not show any discernable change due to irradiation. Surface Cr segregation is observed following high temperature irradiation exposure. This work offers insights into the understanding of Alloy 709 property degradation under high temperature irradiation environments to determine its effectiveness for use in a sodium fast reactor.