2018 | ANNUAL REPORT 99 loops and the α' precipitation can be calculated by dispersed barrier hardening models. The hardening contribution of the α' precipitation is a relatively simple function of density and average diameter of α' precipitations observed in APT.The calculation of irradiation hardening by dislocation loops, on the other hand, requires more-advanced modeling that consider the influence of critical resolved-shear stress on slip systems, habit planes of dislocation loops, and dislocation-density evolution during deformation. Another major advantage of performing in situ synchrotron XRD tensile testing is that dislocation- density evolution during deforma- tion can be obtained using the Williamson-Hall analysis.The in situ tensile study shows similar plasticity behaviors in the low-dose samples and substantially increases dislocation densities at the higher dose samples. HEDM (High-energy X-ray diffraction microscopy) High-energy diffraction microscopy (HEDM) is a non-destructive three dimensional XRD technique that is suitable to characterize mechanical properties of neutron-irradiated samples.The APS 1-ID beamline has developed HEDM to obtain in situ grain-by-grain tensile behavior. Near-field high-energy diffraction microscopy (nf-HEDM) is used to obtain a crystallographic-orientation map of grains. Far-field high-energy diffraction microscopy (ff-HEDM) uses the high-resolution detector in ways similar to the WAXS detector to obtain grain-resolved lattice strains. Figure 12. Cr RIS at VN phase boundary.