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The behavior of solute atoms in an undersaturated Fe-3.3 at.%Ni model alloy upon heavy and light particle irradiations was investigated by Atom Probe Tomography. Whereas first irradiations, performed using 27 MeV Fe ions at 400 °C, highlight significant Ni enrichment on point defect clusters, solute-rich features detected after 2.8 MeV H + ion (400 °C) and 1 MeV electron (320 °C) irradiations are only associated with pre-existent microstructural defects. Nanoindentation tests show no hardening in light particle irradiated samples, strongly suggesting that no dislocation loop formed. These observations put forward the importance of point defect clusters resulting from displacement cascades in Ni clusters' formation. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In situ irradiation in transmission electron microscope following pre-irradiation was performed on Fe-0.6Ni alloy to investigate the growth of dislocation loops under irradiation. The observations showed two types of loop growth behaviour. One type was almost linear growth with irradiation dose, possibly caused by loop absorbing freely migrating defects. The other was abrupt growth with rapid increase in diameter. It was found that nanometre-sized loop might migrate one-dimensionally, following which the large loop could absorb the small loop. This process can result in the abrupt growth of loop and broadening of loop size distribution. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Post irradiation annealing (PIA) clarified the induced versus enhanced controversy regarding nanoscale Mn-Ni-Si precipitate (MNSP) formation in pressure vessel steels. Radiation induced MNSPs would dissolve under high temperature PIA, while radiation enhanced precipitates would be stable above a critical radius (r c). A Cu-free, high Ni steel was irradiated with 2.8MeV Fe2+ ions at two temperatures to generate MNSPs with average radii (r ¯) above and below an estimated r c for PIA at 425°C up to 52 weeks. Atom probe tomography and energy dispersive x-ray spectroscopy showed MNSPs with r < r c dissolved, while those with r > r c slightly coarsened, consistent with thermodynamic predictions. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Massive, thick-walled pressure vessels are permanent nuclear reactor structures that are exposed to a damaging flux of neutrons from the adjacent core. The neutrons cause embrittlement of the vessel steel that grows with dose (fluence), as manifested by an increasing ductile-to-brittle fracture transition temperature. Extending reactor life requires demonstrating that large safety margins against brittle fracture are maintained at the higher neutron fluence associated with beyond 60 years of service. Here synchrotron-based x-ray diffraction and small angle x-ray scattering measurements are used to characterize highly embrittling nm-scale Mn–Ni–Si precipitates that develop in the irradiated steels at high fluence. These precipitates lead to severe embrittlement that is not accounted for in current regulatory models. Application of the complementary techniques has, for the very first time, successfully identified the crystal structures of the nanoprecipitates, while also yielding self-consistent compositions, volume fractions and size distributions. [ABSTRACT FROM AUTHOR]

The irradiation of high-energy particles always leads to the embrittlement of metallic materials. Here, we report an abnormal irradiation toughening phenomenon in a hierarchical structured ZrTi, which results from the irradiation-induced lattice relaxation that yields an enhanced ductility with a slight decrease of strength. Positron annihilation measurements reveal that the lattice relaxation dominantly originates from a recombination of irradiation-induced interstitials (i.e., Ti atoms) with preexisting dislocation-associated vacancies. This study provides an approach to suppress the irradiation-induced brittleness in metallic materials. [ABSTRACT FROM AUTHOR]

In this study, APT and TEM analyses were used to characterise two Zr-based alloys neutron-irradiated to 13.7 dpa. The high spatial and chemical resolution of these techniques has enabled the irradiation-induced nanoscale distribution of solute elements to be characterised. The results on both Zircaloy-2 and low-Sn ZIRLO support previous observations of Fe segregation to planar dislocation arrays with enhanced Sn between. In Zircaloy-2, the APT data in this study have also revealed short-range (∼2 nm) clustering of Fe and Sn atoms both within the Fe-enriched planes and in the regions between dislocation arrays. The resultant microstructure is reminiscent of spinodal decomposition. In low-Sn ZIRLO Nb-rich precipitates formed in the Sn-rich planes. The data in this article enhance our understanding of microstructural evolution in Zr alloys under neutron irradiation and are relevant for predicting changes in the properties of Zr alloys in-service in fission reactors. [Display omitted] [ABSTRACT FROM AUTHOR]