Search

At very high damage levels in ion irradiated samples, the decrease in effective density of the irradiated material due to void swelling can lead to errors in quantifying swelling. HT9 was pre-implanted with 10 appm He and subjected to a raster-scanned beam with a damage rate of ∼1 × 10 −3 dpa/s at 460 o C. Voids were characterized from 0 to 1300 nm. Fixed damage rate and fixed depth methods were developed to account for damage-dependent porosity increase and resulting dependence on depth. The fixed depth method was more appropriate as it limits undue effects from the injected interstitial while maintaining a usable void distribution. By keeping the depth fixed and accounting for the change in damage rate due to reduced density, the steady state swelling rate was 10% higher than calculation of swelling from raw data. This method is easily translatable to other materials, ion types and energies and limits the impact of the injected interstitial. [ABSTRACT FROM AUTHOR]

The microstructures of ferritic-martensitic alloys HT9 and T91 were characterized following 5 MeV Fe ++ ion irradiation to 140 displacements per atom (dpa) at 440 °C with either a raster-scanned or defocused beam. Alloys were pre-implanted with 0–100 appm He and then subjected to either a raster-scanned beam or a defocused beam. Relative to the defocused beam, a raster-scanned beam suppressed microstructural evolution, evidenced by decreased diameter and number densities of voids, loop and precipitates, which lead to decreased void swelling, precipitate volume fraction and total dislocation loop line density. These results were consistent with the Fully Dynamic Rate Theory (FDRT) model which predicts that raster-scanning should lead to a decrease in defect population and suppression of nucleation and growth processes. [ABSTRACT FROM AUTHOR]