b'The indentation size effect that occurs during nanoindentation (NI) testing has been examined on annealed pure Fe and Fe-Cr binary alloys under constant strain rate conditions. In parallel, the effect of matrix strength on the indentation size effect has been examined by performing NI tests on binary Fe-18Cr specimens that were thermally aged at 475C for 100 to Figure 4. Shear stress vs. shear strain900 h in order to produce a wide for 14YWT irradiated in the BOR-60range of matrix hardening associated reactor to 17b dpa at 380C. with Cr-rich alpha prime precipitates (Ben Eftink) of varying precipitate size and density. These fundamental NI samples. The size of Ni/Si-richsingle-effects data are essential to clusters following ion irradiation reduce the quantitative uncertainty was comparable to that from thewhen analyzing the hardening BOR-60 irradiation and the densitycontributions from dislocation was found to be 10-100x lower in DIloops, cavities and precipitates irradiated T91 compared to BOR60in neutron and ion irradiated irradiated T91.9-12Cr steels. To complement NI, shear punch tests were conducted A cluster dynamics model wason neutron irradiated advanced developed to predict microstructuralreactor relevant materials from the evolution in high-energy particleBOR-60 reactor. These tests provide irradiated ferritic martensitic (F/M)a comparison between conventional steels, in which we have recentlyHT-9 and advanced 14YWT at high implemented a model for the biaseddoses up to 35 dpa and temperatures absorption of self-interstitial defectsbetween 380 and 520 C which are at small, nanometer-sized cavities thatrelevant conditions for advanced can provide an intrinsic nucleationfast reactors. The results brought barrier for the onset of void swelling.insights particularly to the impact The model also includes the influenceof irradiation temperature, which is of helium content on modifying theless pronounced in the advancedintrinsic cavity bias. Incorporation of14YWT alloy.cavity bias was effective in creating a nucleation period for void swelling that is commonly observed in experiment.2019|AFC ACCOMPLISHMENTS 185'