Browsing by Author "Lee, TL"

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    Anisotropic behaviours of LPBF Hastelloy X under slow strain rate tensile testing at elevated temperature
    (Elsevier B. V., 2022-06) Yu, CH; Peng, RL; Lee, TL; Luzin, V; Lundgren, JE; Moverare, J
    To improve the understanding of high temperature mechanical behaviours of LPBF Ni-based superalloys, this work investigates the influence of an elongated grain structure and characteristic crystallographic texture on the anisotropic tensile behaviours in LPBF Hastelloy X (HX) at 700 °C. Two types of loading conditions have been examined to analyse the anisotropy related to the building direction (BD), including the vertical loading (loading direction//BD) and the horizontal loading (loading direction ⊥ BD). To probe the short-term creep behaviours, slow strain rate tensile testing (SSRT) has been applied to address the strain rate dependent inelastic strain accumulation. In-situ time-of-flight neutron diffraction upon loading was performed to track the anisotropic lattice strain evolution in the elastic region and the texture evolution in the plastic region. Combined with the post microstructure and fracture analysis, the anisotropic mechanical behaviours are well correlated with the different microstructural responses between vertical and horizontal loading and the different strain rates. A better creep performance is expected in the vertical direction with the consideration of the better ductility and the higher level of texture evolution. © 2022 The Authors. Published by Elsevier B.V. Open access article under the CC BY licence.
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    Measuring residual strain and stress in thermal spray coatings using neutron diffractometers
    (SSRN, 2020-10-14) Faisal, NH; Ahmed, R; Prathuru, AK; Paradowska, AM; Lee, TL
    During thermal spray coating, residual strain (or stress) is formed within the coating and substrates due to many processes (quenching stress, peening effect, deposition temperature, lamella structure) and micro-structural phase changes. It is also known that the residual stress values of thermally sprayed coatings are dependent upon the measurement method. Neutron diffraction technique can provide a non-destructive through-thickness residual strain analysis in thermally sprayed components with a level of detail not normally achievable by other techniques. Despite this advantage, the number of studies involving neutron diffraction analysis in thermal spray coatings remain limited, partly due to the limited number of neutron diffraction strain measurement facilities globally, and partly due to the difficulty is applying neutron diffraction analysis to measure residual strain in the complex thermal spray coating micro-structure. This paper provides a comprehensive guide to researchers planning to use this technique for thermal spray coatings, and reviews some of these studies. ENGIN-X at the ISIS spallation source in the UK is a neutron diffractometer (time-of-flight) dedicated to materials science and engineering with high resolution and versatile capabilities. The focus is on the procedure of using ENGIN-X diffractometer for thermal spray coatings with a view that it can potentially be translated to other neutron diffractometers. Neutron sources worldwide (e.g. Africa, Asia, Australia, Europe, and North America) have been used to measure strains in various materials, and here, we present few examples where thermal spray coatings have been characterized at various neutron sources worldwide, to study the residual strains and micro-structures. © Elsevier Inc.