Browsing by Author "Sun, YL"

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    Electron beam weld modelling of ferritic steel: effect of prior-austenite grain size on transformation kinetics
    (Elsevier B. V., 2020-11-19) Vasileiou, AN; Hamelin, CJ; Smith, MC; Francis, JA; Sun, YL; Flint, TF; Xiong, Q; Akrivos, V
    Ferritic steels experience solid-state phase transformation (SSPT), which causes volumetric changes due to differences in the atomic packing density of different phases in the steel. The importance of the prior austenite grain size (PAGS) as an input physical variable is assessed, for adequately modelling the anisothermal SSPT during welding of ferritic steels. The knowledge of the PAGS value pre-requires a thorough microstructural study of each particular weld, information that might be difficult to acquire. A relationship between hardness, PAGS and phase fractions is proposed to be used to feed in weld models. The case of a single-pass, autogenous, reduced-pressure electron beam weld is used for this study. The adequacy of the finite-element weld model in predicting the micro-constituents, the hardness and the residual stress is demonstrated via comparing the predicted results of the thermo-metallurgical and stress analyses with the set of corresponding experimental data. This work aims at providing a better understanding of the impact of PAGS on transformation kinetics and best practice guidelines for modelling, using an extensively validated electron beam weld model as baseline. © 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
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    Inhomogeneous structure and glass-forming ability in Zr-based bulk metallic glasses
    (Elsevier, 2010-01-01) Sun, YL; Qu, DD; Sun, YJ; Liss, KD; Shen, J
    Recently, a series of quaternary Zr-based bulk metallic glasses (BMGs), i.e., Zr53Cu18.7Ni12Al16.3, Zr51.9Cu23.3Ni10.5Al14.3 and Zr50.7Cu28Ni9Al12.3, have been developed and their glass-forming ability (GFA) increases with Cu concentration. In this work, atomic structures of the three BMGs were rebuilt by reverse Monte Carlo simulations based on the reduced pair distribution functions measured by high energy X-ray diffraction. The results show that a certain amount of substitution of short Zr-Cu, Cu-Cu pairs with long Zr-Zr and Zr-Al pairs enhances the local denser packing of Kasper polyhedral centered by Zr and Al atoms. A cell sub-divided method is proposed to describe the fluctuation of local number density which is found to follow the normal distribution function. The largest possible free volume in the three alloys is found to approaches to 3.8 angstrom. For the three alloys, the enhancement of GFA with increasing Cu content is due to the increase in the fluctuation degree of local density instead of the dense packing. © 2010, Elsevier Ltd.