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The influence of ion irradiation on structural rejuvenation and relaxation in a Zr-based metallic glass (MG) is investiagted. The MG can be structurally rejuvenated with increasing irradiation dosage from 0 to 3 dpa, which reflects in increased activation volumes of shear-transformation zones. However, structural relaxation dominates at a high irradiation dosage (4 dpa) resulting in higher hardness. The anelastic-relaxation processes in the irradiated MG can be understood in terms of the coordination mechanism of the deformation modes associated with free volume. Ion irradiation appears to be a promising and effective way to modify MGs and to, thus, manipulate plastic flow. Image, graphical abstract [ABSTRACT FROM AUTHOR]

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]

Electron irradiation induced phase separation in a sodium borosilicate glass was studied in situ by analytical electron microscopy. Distinctly separate phases that are rich in boron and silicon formed at electron doses higher than 4.0 × 1011 Gy during irradiation. The separated phases are still in amorphous states even at a much high dose (2.1 × 1012 Gy). It indicates that most silicon atoms remain tetrahedrally coordinated in the glass during the entire irradiation period, except some possible reduction to amorphous silicon. The particulate B-rich phase that formed at high dose was identified as amorphous boron that may contain some oxygen. Both ballistic and ionization processes may contribute to the phase separation. [Copyright &y& Elsevier]

• High temperature water combined with irradiation induces in oxidation of grain boundaries that weaken the boundaries. • Applied tensile stress enhances the rate of grain boundary oxidation. • Deformation induced dislocation channels create local stresses sufficient to crack a grain boundaryweakened by oxidation. • Fracture of the oxidized grain boundary allows for oxidation of the boundary beneath the crack tip. • Oxidation of silicon at the grain boundary forms highly soluble amorphous silica that aids crack extension via dissolution. Irradiation assisted stress corrosion cracking (IASCC) is a form of intergranular stress corrosion cracking that occurs in irradiated austenitic alloys. It requires an irradiated microstructure along with high temperature water and stress. The process is ubiquitous in that it occurs in a wide range of austenitic alloys and water chemistries, but only when the alloy is irradiated. Despite evidence of this degradation mode that dates back to the 1960s, the mechanism by which it occurs has remained elusive. Here, using high resolution electron backscattering detection to analyze local stress-strain states, high resolution transmission electron microscopy to identify grain boundary phases at crack tips, and decoupling the roles of stress and grain boundary oxidation, we are able to unfold the complexities of the phenomenon to reveal the mechanism by which IASCC occurs. The significance of the findings impacts the mechanical integrity of core components of both current and advanced nuclear reactor designs worldwide. [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]

Progress in understanding radiation damage in structural materials is hampered by the lack of test reactors, long irradiations and high cost. Here we show that through strict control of experimental parameters and accounting for He production and damage-rate differences, the microstructure of ion-irradiated ferritic-martensitic steel closely resembles that created in-reactor across the full range of microstructure features. The level of agreement establishes for the first time the capability to tailor ion irradiation to emulate in-reactor radiation damage. [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]

A radiation-induced order–disorder transformation occurs in many A2B2O7 pyrochlore structure-types by disordering of the A- and B-site cations, as well as anion vacancies. The ionic conductivity increases up to two orders of magnitude due to this order–disorder transformation. This irradiation-induced order–disorder transition has been examined in detail using ion beam irradiations and in situ transmission electron microscopy. Under ion irradiation, the ordered pyrochlore superstructure transforms to an anion-disordered pyrochlore prior to a final transformation to a cation-disordered defect-fluorite structure-type. The anion-disordered pyrochlore structure displays a partial ordering of the A- and B-site cations and complete disordering on the anion array—as evidenced by the disappearance of characteristic diffraction maxima resulting from ordering of the oxygen sublattice. These results suggest that anion disorder precedes cation disordering in the pyrochlore structure. [Copyright &y& Elsevier]