2018 | ANNUAL REPORT 91 iron to Fe–Cr binary model alloys to Fe–Cr–C ternary model alloys to commercial and developmental alloys.This spectrum of simple-to- complex Fe–Cr base alloys provide the basis for assessing the underlying radiation performance processes even in complex alloy systems.The new level of understanding on the irradia- tion performance of this alloy system will also facilitate the development of modeling capabilities to better predict future alloy performance and development. A set of state-of-the-art techniques has been used for the characterization of the irradiated alloys.Transmission electron microscopy (TEM), atom probe tomography (APT), and posi- tron annihilation spectroscopy (PAS) were used to characterize the irradi- ated microstructure. Nanoindentation and in situ synchrotron wide-angle X-ray scattering (WAXS) were used to study mechanical properties. Figure 1 is an example of TEM results comparing the loop structure of iron (Fe) and Fe–9Cr alloy that underwent the same neutron irradiation. It is clear that in Fe the dislocations are decorated by small black-dot disloca- tion loops, and in Fe–9Cr a homoge- neous loop structure was observed. The reason is that the addition of chromium reduces the mobility of a/2 〈111〉 loops and prevents them from migrating to pre-existing dislocations, resulting in a uniform loop distribution. Another important feature commonly observed in irradiated high-Cr ferritic alloys are Cr-rich α' precipitates. Previous studies indicated that α' precipitation is a radiation-enhanced process, rather than radiation-induced. Interestingly, the α' precipitation was found highly dependent on the bombarding radiation particles and Alloy Temp (C) Dose (dpa) Specimen Types Model Alloys Fe, Fe-9Cr, Fe-12Cr, Fe-14Cr, Fe-19Cr, also Fe-9Cr & Fe-12Cr with 0.1, 0.2 or 0.5 wt% C 300, 450, 550 0.01, 0.1, 0.5, 1, 5, 10 TEM, MiniatureTensile Commercial Alloys T91, HT-9 300, 450, 550 0.01, 0.1, 0.5, 1, 5, 10 TEM, MiniatureTensile Developmental Alloys MA-957 300, 450, 550 0.01, 0.1, 0.5, 1, 5, 10 TEM, MiniatureTensile Table 1. Target irradiation alloy matrix, specimen types, and exposure conditions.