Browsing by Author "Dong, BS"

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    Development of a new powder-bed arc additive manufacturing approach for producing high entropy alloys
    (Australian Nuclear Science and Technology Organisation, 2021-11-26) Dong, BS; Muránsky, O; Zhu, Hl; Muránsky, O; Wang, ZY; Reid, M; Li, HJ
    High entropy alloys (HEAs) have gained significant attention over the past decade from both academic and industrial communities due to their unique design concept and promising properties. The manufacturing of this emerging material with desired properties remains challenging. Most of previous work utilized conventional vacuum arc melting and casting methods for producing HEAs. However, the disadvantage of typical casting microstructure, columnar dendrite and serious chemical segregation, causes serious deterioration to their mechanical properties. A new powder-bed arc additive manufacturing (PAAM) has been developed at the University of Wollongong for producing HEAs. This approach, with a high level of flexibility for controlling the forming process and the characteristic rapid solidification, enables the tailoring of the microstructure through the process control and the effective reduction of the chemical segregation in these compositionally complexed alloys. Additionally, compared with the laser and electron beam based additive manufacturing, PAAM is advantageous for higher production rate hence it is promising in industrial applications for producing bulk components in shorter period. The production of a eutectic AlCoCrFeNi2.1 HEA using this new PAAM approach will be presented to demonstrate its capability. The characterisation work shows that the produced AlCoCrFeNi2.1 samples have a lamellar microstructure consisting of the soft but ductile face-centered cubic (FCC) phase as well as the hard body-centered-cubic (BCC) phase. The material demonstrates a remarkable combination of excellent ultimate tensile strength (719 MPa) and ductility (elongation ~27%). The current work has demonstrated that the developed PAAM process is promising for producing HEA components with desired properties. © The Authors
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    Development of a new powder-bed arc additive manufacturing approach for producing high entropy alloys
    (Materials Australian and The Australian Ceramic Society, 2022-06-01) Dong, BS; Wang, ZY; Pan, Z; Li, HJ
    High entropy alloys (HEAs) have gained significant attention over the past decade from both academic and industrial communities due to their unique design concept and promising properties. The manufacturing of this emerging material with desired properties remains challenging. A new powder-bed arc additive manufacturing (PAAM) has been developed at the University of Wollongong for producing HEAs. This approach, with a high level of flexibility for controlling the forming process and the characteristic rapid solidification, enables the tailoring of the microstructure through the process control and the effective reduction of the chemical segregation in these compositionally complexed alloys. Additionally, compared with the laser and electron beam based additive manufacturing, PAAM is advantageous for higher production rate hence it is promising in industrial applications for producing bulk components in shorter period. The production of a eutectic AlCoCrFeNi2.1 HEA using this new PAAM approach will be presented to demonstrate its capability. Then, the FeCr0.4V0.3Ti0.2Ni1.3 HEA with low neutron cross-section is successfully designed and fabricated in this system. The good tensile properties of this novel HEA make it become a potential candidate as a structural material in the future nuclear industry.
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    Low neutron cross-section FeCrVTiNi based high-entropy alloys: design, additive manufacturing and characterization
    (OAE Publishing, 2022-01-13) Dong, BS; Wang, ZY; Zhu, HL; Muránsky, O; Qiu, ZJ; Shen, C; Pan, ZX; Li, HJ
    The development of high-entropy alloys (HEAs) based on the novel alloying concept of multi-principal components presents opportunities for achieving new materials with desired properties for increasingly demanding applications. In this study, a low neutron cross-section FeCrVTiNi-based HEA was developed for potential nuclear applications. A face-centred cubic (FCC) HEA with the nominal composition of FeCr0.4V0.3Ti0.2Ni1.3 is proposed based on the empirical thermodynamic models and the CALculation of PHAse diagrams (CALPHAD) calculation. Verifications of the predictions were performed, including the additive manufacturing of the proposal material and a range of microstructural characterizations and mechanical property tests. Consistent with the prediction, the as-fabricated HEA consists of a dominant FCC phase and minor Ni3Ti precipitates. Moreover, significant chemical segregation in the alloy, as predicted by the CALPHAD modelling, was observed experimentally in the produced dendritic microstructure showing the enrichment of Ni and Ti elements in the interdendritic regions and the segregation of Cr and V elements in the dendritic cores. Heterogenous mechanical properties, including microhardness and tensile strengths, were observed along the building direction of the additively manufactured HEA. The various solid solution strengthening effects, due to the chemical segregation (in particular Cr and V elements) during solidification, are identified as significant contributing factors to the observed mechanical heterogeneity. Our study provides useful knowledge for the design and additive manufacturing of compositionally complex HEAs and their composition-microstructure-mechanical property correlation. © The Author(s) 2022
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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.