Nuclear Science User Facilities 60 high strain-hardening rate in the unirradiated condition.The εu in the 14Cr oxide-dispersion-strengthened nanostructured ferritic alloy was even less affected by irradiation, and the strain-hardening rate was remarkably unchanged. Again, this is likely due to the high rate of strain hardening in both conditions, primarily due to the very fine-grained microstructure, which promotes the formation of geometrically necessary dislocations. The use of accelerated charged-particle irradiations as a surrogate for neutron irradiation, while potentially advanta- geous, is not without challenges. One significant challenge is extracting ∆σy [or more generally, σ(ε)] data from ion-implantation depths of only a few µm. In principle, this type of analysis can be done using nano-indentation (NI) methods. However, it is critical that techniques to transfer NI to bulk σ(ε) be developed and validated.To this end, small disc specimens punched from the end tabs of the tensile specimens of the same six samples considered in Figure 6, plus two addi- tional UCSB-1 library irradiated steels, were subjected to NI measurements [13] to develop correlations between NI at various depths, and the bulk- irradiated steels tensile properties.The NI and tensile data were analyzed with various property-property correla- tion models.As shown in Figure 7a, a reasonably good correlation was found between high-load Berkovich microhardness (Hµ, somewhat akin toVickers microhardness) and two measures of NI hardness taken at a sufficient penetration depth to avoid size effects. Unfortunately, the correla- tion between NI hardness and tensile properties was more scattered and the corresponding ∆σy were not well predicted by the NI measurements. These results underscore the caution required in interpreting NI data and demonstrate that additional research is needed to develop better property- property correlations. The microstructure and mechanical behavior of the Fe-6Cr in the unir- radiated, self-ion-irradiated and neutron-irradiated conditions were measured and compared [14]. Ion irradiations were performed to the same dpa (≈1.8) and similar tempera- tures, but at much higher dpa rates. The mechanical property characteriza- tion involved both NI and micro- cantilever bend tests for a wide range of beam dimensions to study the interrelationships between irradiation hardening and plasticity size effects. TEM found dislocation loop densities about 3 × 1022 /m3 for the neutron- irradiated condition versus only 1.4 × 1022 /m3 for the ion-irradiated alloy, although these differences are within typical scatter. Notably, Cr segregation to loops was only found for the neutron-irradiated case.The NI hardness increase due to neutron irradiation was about ≈3 GPa, which is roughly similar to an estimate of ≈2.6 GPa, based onVickers microhard- ness data.The corresponding ion-irra- diation hardening was much less, at about 1 GPa.The large difference was judged to be only partly due to the effects of dpa rate and corresponding microstructural differences. TEM has been used to characterize steels and one 14Cr oxide-dispersion- strengthened nanostructured ferritic alloy, are shown in Figure 6 [12]. Engineering stress-strain s(e) curves for tests at 298 and 573 K were analyzed using a finite-element-based inverse method developed to derive the corresponding σ(ε) curves, both before and after irradiation. Increases in yield stress (∆σy) and reductions in uniform strain ductility (∆εu) were observed in all cases.The effect of irradiation on εu can be understood in terms of the flow instability condition dσ(εu)/dε = σ(εu). The irradiated σ(ε) curves fall into three categories of post-yield behavior: initial strain softening, followed by perfectly plastic, nearly perfectly plastic, and reduced or unaffected strain hardening. The irradiation-induced increases in the average plastic flow stress in the range of 0 to 10% strain, ∆σf, is gener- ally smaller than the corresponding ∆σy due to the reduction in strain hardening.The tensile data were also analyzed to establish relations between ∆σy and corresponding changes in the ultimate stress, ∆σu, as well as the effects of both test temperature and the unirradiated yield stress (σyu).The latter shows that higher σyu correlates with lower ∆σy, due to quadratic dispersed- barrier strengthening superposition effects. In five out of six cases, the effects of irradiation are generally consistent with previous results on these types of alloys. However, the particular heat of the 12Cr HT-9 tempered martensitic steel in this study has a much higher irradiated strain- hardening rate and εu than observed in earlier heats.This difference is likely due to the correspondingly