| 1. |
- Topping, Matthew, et al.
(författare)
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The effect of iron on dislocation evolution in model and commercial zirconium alloys
- 2018
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Ingår i: ASTM Special Technical Publication. - 0066-0558. ; STP 1597, s. 796-822
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Konferensbidrag (refereegranskat)abstract
- Although the evolution of irradiation-induced dislocation loops has been well correlated with irradiation-induced growth phenomena, the effect of alloying elements on this evolution remains elusive, especially at low fluences. To develop a more mechanistic understanding of the role iron has on loop formation, we used state-of-the-art techniques to study a proton-irradiated Zr-0.1Fe alloy and proton- and neutron-irradiated Zircaloy-2. The two alloys were irradiated with 2-MeV protons up to 7 dpa at 350°C and Zircaloy-2 up to 14.7 × 1025n • m-2, approximately 24 dpa, in a boiling water reactor at approximately 300°C. Baseline transmission electron microscopy showed that the Zr3Fe secondary-phase particles in the binary system were larger and fewer in number than the Zr (Fe, Cr)2and Zr2(Fe, Ni) particles in Zircaloy-2. An analysis of the irradiated binary alloy revealed only limited dissolution of Ze3Fe, suggesting little dispersion of iron into the matrix, while at the same time a higher 〈a〉-loop density was observed compared with Zircaloy-2 at equivalent proton dose levels. We also found that the redistribution of iron during irradiation led to the formation of iron nanoclusters. A delay in the onset of 〈c〉-loop nucleation in proton-irradiated Zircaloy-2 compared with the binary alloy was observed. The effect of iron redistributed from secondary-phase particles because of dissolution on the density and morphology of 〈a〉 and 〈c〉 loops is described. The implication this may have on irradiation-induced growth of zirconium fuel cladding is also discussed.
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| 2. |
- Zhang, Kai, et al.
(författare)
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Unravelling dynamic recrystallisation in a microalloyed steel during rapid high temperature deformation using synchrotron X-rays
- 2024
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 278
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure evolution during high-strain rate and high-temperature thermo-mechanical processing of a 44MnSiV6 microalloyed steel is investigated using in situ synchrotron high-energy powder X-ray diffraction. The conditions selected replicate a newly developed near solidus high-strain rate process designed for reducing raw material use during the hot processing of steels. High temperatures (exceeding 1300 °C) and high strain rate ε˙ = 9 s-1 processing regimes are explored. The lattice strains and dislocation activity estimated from diffraction observations reveal that the microstructure evolution is primarily driven by dynamic recrystallisation. A steady-state stress regime is observed during deformation, which develops due to intermittent and competing work hardening and recovery processes. The texture evolution during the heating, tension, shear deformation and cooling stages is systematically investigated. The direct observation of phase evolution at high-temperature and high-strain rate deformation enables a comprehensive understanding of new manufacturing processes and provides deep insights for the development of constitutive models for face-centred cubic alloys.
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| 3. |
- Zhang, Zhenbo, et al.
(författare)
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Strain localisation and failure at twin-boundary complexions in nickel-based superalloys
- 2020
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Twin boundaries (TBs) in Ni-based superalloys are vulnerable sites for failure in demanding environments, and a current lack of mechanistic understanding hampers the reliable lifetime prediction and performance optimisation of these alloys. Here we report the discovery of an unexpected gamma '' precipitation mechanism at TBs that takes the responsibility for alloy failure in demanding environments. Using multiscale microstructural and mechanical characterisations (from millimetre down to atomic level) and DFT calculations, we demonstrate that abnormal gamma '' precipitation along TBs accounts for the premature dislocation activities and pronounced strain localisation associated with TBs during mechanical loading, which serves as a precursor for crack initiation. We clarify the physical origin of the TBs-related cracking at the atomic level of gamma ''-strengthened Ni-based superalloys in a hydrogen containing environment, and provide practical methods to mitigate the adverse effect of TBs on the performance of these alloys.
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