Browsing by Author "Laws, KJ"

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    A combined DFT and NPD approach to determine the structure and composition of the ε-phase of tungsten boride
    (Elsevier, 2023-10-15) Setayandeh, SS; Stansby, JH; Obbard, EG; Brand, MI; Miskovic, DM; Laws, KJ; Peterson, VK; Astbury, JO; Wilson, CL; Irukuvarghula, S; Burr, PA
    The ε-phase of tungsten boride, conventionally labelled as W2B5, has been identified as a promising candidate for shielding application in spherical tokamak fusion reactors. However, further research has been hindered by a lack of agreement on the structure and even composition of the ε-phase. Here, we identify the stable crystal structure and stoichiometry range of ε tungsten borides through a combination of ab initio simulations and neutron diffraction of isotopically enriched samples. We considered the ability to accommodate hypo-stoichiometry in six published structures of the ε phase. Chemical disorder was modelled using configurational ensembles to account for entropy of non-stoichiometry. We show that two W2B4-x structures (with x=∼0.25 − 0.5), with space group symmetry P63/mmc and P63/mcm, appear to be thermodynamically stable. These candidate compounds have 6.2 − 7.8 at.% less B than the W2B5 composition reported in exiting phase diagrams. We confirm these findings by means of neutron powder diffraction, performed on 11B-enriched arc-melted and crushed samples. Rietveld refinement using the neutron data shows the ε-phase to be better described as W2B3.60(2) (P63/mcm), in keeping with density functional theory (DFT) calculations. Linear change in DFT-derived lattice parameters of the candidates for the ε-phase proposes a simple model to assess the tungsten boride composition by measuring the lattice parameter (e.g. by X-ray diffraction. The simulations also reveal that the material can accommodate a range of stoichiometric variations (via B vacancies) with relatively small stored energy, which is a desirable feature for neutron shielding application. © 2023 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc. Open Access CC-NC-ND
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    Corrosion performance of Ni-based structural alloys for applications in molten-salt based energy systems: experiment & numerical validation
    (Elsevier, 2021-09) Lee, M; Muránsky, O; Karatchevtseva, I; Huang, HF; Laws, KJ
    The molten salt corrosion performance of a Y2O3-strengthened Ni-Cr alloy (MA754®) designed for high temperature applications (> 750 °C) was compared to purpose-designed Ni-Mo-Cr molten-salt resistant alloys (GH3535, HASTELLOY-N®). The significant material mass loss of MA754® alloy is attributed to its higher Cr-content. However, Y2O3 dispersoids are shown to play only a minor role in the corrosion performance of this oxide-dispersion-strengthened (ODS) alloy. The current result, thus, points to the possibility for the development of low Cr-content ODS alloys that combines the high-temperature properties of ODS MA754® alloy with good molten salt corrosion resistance of well-established GH3535 and HASTELLOY-N® alloys. Crown Copyright © 2021 Published by Elsevier Ltd