Browsing by Author "Wu, BT"

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    Effects of post heat treatment on the microstructure and mechanical properties of wire arc additively manufactured Hastelloy C276 alloy
    (Elsevier, 2021-07) Qiu, ZJ; Wu, BT; Wang, ZY; Wexler, D; Carpenter, K; Zhu, HL; Muránsky, O; Zhang, JR; Li, HJ
    Post-processing is often inevitable for most additively manufactured components in order to improve material properties and product quality. In this study, the influence of post-heat treatments (PHTs) at 871 °C and 1177 °C on the microstructure and mechanical properties of a nickel-base Hastelloy C276 alloy prepared using wire arc additive manufacturing (WAAM) were investigated. The results showed that after a PHT at 871 °C, the as-built alloy was strengthened due to the formation of a large amount of Mo-rich nano-sized μ phase in the interdendritic areas. This was at the expense of a significant ductility loss. In contrast, no μ phase precipitates were observed after PHT at 1177 °C. Furthermore, the 1177 °C treatment led to the dissolution of the Mo-rich p phase which was present in the as-built sample, increased solid-solution strengthening, and improvements in both strength and ductility concurrently. This study enables an improved understanding of post-processing-microstructure-property inter-relationships for Hastelloy C276 alloy prepared by WAAM, providing guidelines for further microstructure optimization through PHT to improve the material's mechanical properties. © 2021 Elsevier Inc.
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    Microstructural characterisation and hardness assessment of wire arc cladded Hastelloy C276 on creep resistant steel P91
    (Elsevier, 2022-07) Wu, BT; Qiu, ZJ; Dong, BS; Muránsky, O; Zhu, HL; Wang, ZY; Pan, ZX; Li, HJ
    A new structure with nickel-based Hastelloy C276 alloy cladding on creep resistant steel P91 was developed in this study for nuclear applications. The microstructure, including precipitation and grain size, boundaries, orientation and hardness distribution of cladding structures with/without post heat treatment were explored using a range of microscopy techniques and hardness testing. The results show that the as-cladded structure exhibits highly hierarchical heterogeneity, which is mainly related to the remarkably coarse-grained microstructure in the heat-affected zone on the steel side, and typically columnar dendrites formed on the Hastelloy side. After tempering heat treatment, the specimen exhibits re-orientated grains and homogenized microstructure. Meanwhile, the ratio of high angle grain boundaries (HAGBs) in steel regions significantly increases, and the hardness values turn even distribution. This study achieves a sound metallurgical bonding between two structural materials and offers insights into the development of dissimilar metal components with in-site specific properties. © 2022 The Author(s). Published by Elsevier B.V.
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    On the development of pseudo-eutectic AlCoCrFeNi2.1 high entropy alloy using Powder-bed Arc Additive Manufacturing (PAAM) process
    (Elsevier, 2021-01-20) Dong, BS; Wang, ZY; Pan, ZX; Muránsky, O; Shen, C; Reid, M; Wu, BT; Chen, XZ; Li, HJ
    A new Powder-bed Arc Additive Manufacturing (PAAM) processing which includes on-line remelting of deposited material has been developed for the manufacturing of high entropy alloys (HEAs) based on an existing AlCoCrFeNi2.1 pseudo-eutectic system. The remelting process is typically applied in the arc melting process to improve the homogeneity of prepared material. We investigated the microstructure and mechanical properties of produced AlCoCrFeNi2.1 HEA after applying a remelting process (1, 3, and 6 times) on each deposited layer. The results show the formation of the pseudo-eutectic microstructure, which consists of relatively large columnar grains of the dominant FCC phase (~90 wt%) and fine dendritic grains of the minor BCC phase (~10 wt%). The applied layer-remelting process shows negligible effects on the phase fractions and their compositions, however, it significantly degraded the tensile strength and ductility of prepared alloys. Particularly, the ductility of the alloy reduced dramatically from about 27% after one time layer-remelting to only about 3% after 3 times layer-remelting. This is rationalised by the significant localisation of thermally induced plasticity caused by repeated remelting of deposited material. We also show that this thermally induced plasticity leads to an increased amount of local misorientation in both constitute phases, which suggests an increased amount of stored dislocations in the microstructure. Despite the potentially strain hardening due to this accumulation of the thermally induced plasticity, the appreciable growth and constrained dendritic morphology of BCC grains that developed after remelting play a prevailing role on the materials strength, which limit the interfacial strengthening of the eutectic microstructure and consequently result in the loss of the tensile strength. The obtained results will assist in the further development and microstructure optimisation of novel HEAs using powder-based additive manufacturing processes. © 2021 Elsevier B.V.