Browsing by Author "Preuss, M"

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    From solid solution to cluster formation of Fe and Cr in α-Zr
    (Elsevier B.V., 2015-12-01) Burr, PA; Wenman, MR; Gault, B; Moody, MP; Ivermark, M; Rushton, MJD; Preuss, M; Edwards, L; Grimes, RW
    To understand the mechanisms by which the re-solution of Fe and Cr additions increase the corrosion rate of irradiated Zr alloys, the solubility and clustering of Fe and Cr in model binary Zr alloys was investigated using a combination of experimental and modelling techniques — atom probe tomography (APT), x-ray diffraction (XRD), thermoelectric power (TEP) and density functional theory (DFT). Cr occupies both interstitial and substitutional sites in the α-Zr lattice; Fe favours interstitial sites, and a low-symmetry site that was not previously modelled is found to be the most favourable for Fe. Lattice expansion as a function of Fe and Cr content in the α-Zr matrix deviates from Vegard's law and is strongly anisotropic for Fe additions, expanding the c-axis while contracting the a-axis. Matrix content of solutes cannot be reliably estimated from lattice parameter measurements, instead a combination of TEP and APT was employed. Defect clusters form at higher solution concentrations, which induce a smaller lattice strain compared to the dilute defects. In the presence of a Zr vacancy, all two-atom clusters are more soluble than individual point defects and as many as four Fe or three Cr atoms could be accommodated in a single Zr vacancy. The Zr vacancy is critical for the increased apparent solubility of defect clusters; the implications for irradiation induced microstructure changes in Zr alloys are discussed. © 2015 Elsevier B.V.
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    In situ study of the stress relaxation during aging of nickel-base superalloy forgings
    (Springer Nature, 2019-06-03) Aba-Perea, PE; Withers, PJ; Priling, T; Paradowska, AM; Ma, D; Preuss, M
    Nickel-base superalloys are conventionally aged in order to develop a favorable microstructure as well as to relieve residual stresses. Here neutron diffraction was used to follow the evolution of residual stress during aging in Inconel 718 and Udimet 720LI for the first time by a combination of in situ and ex situ measurements. First, the quench-induced stress profiles were determined for different geometries of Inconel 718 forgings confirming that the amplitude of stress is not significantly affected by the thickness of the component. It was followed by in situ residual stress analysis using neutron diffraction during aging/annealing treatments at 650 °C, 720 °C, and 750 °C. Almost 90 pct of stress relaxation was found to occur primarily during heating to the aging temperature as a result of a combination of plasticity and early-stage creep relaxation. Creep-like stress relaxation was observed to evolve at a diminishing rate during the isothermal treatment of Inconel 718 at 720 °C and 750 °C, while no further stress relaxation occurred at 650 °C. This means that a change in hold temperature might have a more immediate impact on stress relaxation than a change in duration of heat treatment. The post-aging ex situ measurements showed that a heat treatment at 750 °C for 8 hours reduced the stresses by approximately 70 pct in Inconel 718. By comparison, when heat treating Udimet 720LI in the same way only a 20 pct stress reduction was observed, which is explained by the higher creep resistance of this alloy. © 2021 Springer Nature Switzerland AG
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    On the microstructure and high-temperature stability of nano-grained Zircaloy-4
    (Elsevier, 2022-03-15) Chen, L; Wang, ZY; Zhu, HL; Burr, PA; Qu, JT; Huang, Y; Balogh, L; Preuss, M; Muránsky, O
    A nano-grained microstructure of an α-Zr alloy (Zircaloy-4) was produced by high-pressure torsion, which shows evidence of a metastable ω-Zr phase, rather than β-Zr, determined by combining synchrotron X-ray diffraction and detailed electron microscopy observations. The ω-Zr phase is retained at ambient conditions and shows a new orientation relationship of [1011]α // [1100]ω and (1011)α // (1120)ω with the α-Zr matrix but is thermally unstable, fully reverting back to α-Zr phase upon heating above 350 °C. © 2021 Acta Materialia Inc. Published by Elsevier Ltd.