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The growth of M 2 X phase in HT9 irradiated to high dpa was explored using self-ion irradiation. HT9 was pre-implanted with 10 appm He and irradiated with a raster-scanned Fe 2+ beam with a damage rate of ∼1 × 10 −3 dpa/s at 460 °C. The precipitation of M 2 X was observed and a combination of high resolution transmission electron microscopy (HRTEM), energy filtered transmission electron microscopy (EFTEM) and diffraction analysis was used to characterize the Cr-rich carbide observed at 250 dpa and above. Cr 2 C was determined to be semi-coherent with the matrix such that [ 100 ] C r 2 C / / [ 100 ] α and [ 001 ] C r 2 C / / [ 10 1 ¯ ] α .with a = 2.71 Å and c = 2.82 Å. [ABSTRACT FROM AUTHOR]

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]

We report a systematic study of the effects of a 400 keV helium ion beam irradiation on the surface morphology and crystal structure of Ti 3 AlC 2 by combined scanning electron microscopy, grazing incidence X-ray diffraction and transmission electron microscopy. Helium irradiation experiments were performed at both room temperature and 500 °C, respectively, with fluence up to 2.0 × 10 17 He + /cm 2 . After irradiation, intragranular orientated cracks grew along the (10 1 ¯ 0) Ti3AlC2 plane and the surface has started to exfoliate. The formation of the cracks is mainly attributed to the reduction of the lattice parameter along the a direction induced by ion irradiation, and the crack growth is affected by the grain size and the content of impurity phase TiAl 3 . The surface exfoliation is due to the blistering of He bubbles at the projected depth. [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]

The behavior of the precipitate in a Zr-1.6Sn-0.6Nb-0.2Fe-0.1Cr alloy under a 2 MeV proton irradiation was studied by transmission electron microscopy (TEM). The plan-view TEM specimens were prepared by a focused ion beam (FIB) lift-out method. It is confirmed that the Zr(Fe,Cr,Nb)2 precipitate with the hexagonal close packed (hcp) structure is the major secondary phase particle (SPP) in this zirconium alloy. At irradiation temperature of 360°C, the Zr(Fe,Cr,Nb)2 precipitate starts to be partially amorphized when the zirconium alloy was irradiated to 3.9 dpa, and was completely amorphized at 8.2 dpa. The mechanism for the Zr(Fe,Cr,Nb)2 precipitate amorphization under proton irradiation is attributed to the Fe diffusion from the Zr(Fe,Cr,Nb)2 phase to the zirconium alloy matrix. The current research indicates that the Zr-1.6Sn-0.6Nb-0.2Fe-0.1Cr alloy has lower irradiation resistance than that of Zircaloy-4, but the results still need to be further verified by its irradiation resistance with respect to neutron irradiation. [ABSTRACT FROM AUTHOR]