Browsing by Author "Yu, CH"

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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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    Effect of scan rotation on the microstructure development and mechanical properties of 316L parts produced by laser powder bed fusion
    (Elsevier B.V., 2020-05) Leicht, A; Yu, CH; Luzin, V; Klement, U; Hryha, EM
    Additive manufacturing possesses appealing features for producing high-performance components, for a wide range of materials. One of these features is the ability to locally tailor the microstructure and in turn, the mechanical properties. This study investigates how the microstructure of stainless steel 316L parts produced by laser powder bed fusion are affected by alternating the laser scan orientation. The microstructure consists of large elongated grains with a fine cell substructure. This study established the correlation between the orientation of this substructure and the crystallographic orientation. The results show that by producing parts without any rotation a quite unique crystallographic orientation can be achieved. The grain structure primarily consisted of large 〈101〉 oriented grains, that were separated by thin bands of small 〈100〉 oriented grains with respect to the building direction. As rotation was added these bands were eliminated. Samples that were produced without any rotation generated the highest tensile strength (527 ± 5.4 MPa), yield strength (449 ± 2.4 MPa) and ductility (58 ± 1.3%). The lowest mechanical properties were obtained for samples that were produced using a scan rotation of 67° with the tensile strength of 485 ± 4.8 MPa, yield strength of 427 ± 5.4 MPa and ductility of 50 ± 1.3%. This indicates that cell orientation and crystallographic orientation plays an essential role in the tensile properties of 316L parts produced by laser powder bed fusion (L-PBF). © 2020 Elsevier Inc.