Browsing by Author "Yang, C"
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- ItemAnnealing-induced strengthening and stabilization in ultrafine-grained Al and Al–Mg alloys prepared by rapid powder consolidation(Elsevier, 2022-01-26) Zhou, DS; Bu, YF; Muránsky, O; Geng, HW; Sun, BH; Yang, C; Zhang, DLAnnealing usually softens Al–Mg based alloys due to grain coarsening. This work shows that annealing induces strengthening in bulk ultrafine-grained Al and Al-(2.5, 5 and 7.5) at.% Mg samples fabricated by mechanical alloying and rapid powder extrusion. Experimental investigation of the microstructure of the annealed samples reveals that the annealing promotes in-situ formation of nanoscale dispersoids which strongly suppresses grain growth and recrystallization. The in-situ formed nanodispersoids warrant high thermal stability of the ultrafine-grained matrix microstructure and improve the strength of the as-extruded samples while maintaining their good ductility. The present findings offer an exciting pathway in developing thermally stable ultrafine-grained Al–Mg based alloys with a notable combination of high strength and good ductility. © 2021 Elsevier B.V
- ItemCorrosion performance of Ni-16%wt.Mo-X%wt.SiC alloys in FLiNaK molten salt(Elsevier, 2018-10-01) Yang, C; Muránsky, O; Zhu, HL; Karatchevtseva, I; Holmes, R; Avdeev, M; Jia, YY; Huang, HF; Zhou, XTThe corrosion performance of Ni-16%wt.Mo-X%wt.SiC (X = 0.5, 1.5, 2.0, 2.5 and 3.0) alloys prepared via mechanical alloying followed by consolidation using spark plasma sintering (SPS) from pure Ni, Mo and SiC powders is investigated. Corrosion testing at 650 °C/200 h in FLiNaK molten salt showed that increasing the volume fraction of SiC in the initial Ni-Mo-SiC powder mixture leads to formation of large amount of Mo2C precipitates, which readily dissolve into FLiNaK molten salt. Hence, only the corrosion resistance of NiMo-SiC alloys with a low SiC content (<2 wt.%) is comparable to that of Hastelloy-N® alloy. © 2018 Elsevier Ltd. All rights reserved.
- ItemThe effect of grain size and dislocation density on the tensile properties of Ni-SiCNP composites during annealing(Springer Nature, 2016-02-12) Yang, C; Huang, HF; Thorogood, GJ; Jiang, L; Ye, XX; Li, ZJ; Zhou, XTThe grain size refinement, enhancement of mechanical properties, and static recrystallization behavior of metallic nickel-silicon carbide nano-particle (Ni-3wt.%SiCNP) composites, milled for times ranging from 8 to 48 h have been examined. One set of Ni-SiCNP composite samples were annealed at 300 °C for 250 h, while the other set of samples were maintained at room temperature for control purposes (reference). The electron backscatter diffraction results indicate that the grain size of the annealed Ni-SiCNP composite was refined due to grain restructuring during static recrystallization. The x-ray diffraction results indicate that low-temperature annealing effectively reduced the density of dislocations; this can be explained by the dislocation pile-up model. Additionally, the tensile tests indicated that the annealed Ni-SiCNP composite had a significant increase in strength due to an increase of the Hall–Petch strengthening effect with a slight increase in the total elongation. The decrease of dislocation pile-up in the grain interiors and the increase in grain boundary sliding are assumed to be the main mechanisms at play. The relationship between the microstructural evolution and the variation of tensile properties is examined in this study. © 2016 ASM International. Published by Springer Nature.
- ItemThe effect of milling time on the microstructural characteristics and strengthening mechanisms of NiMo-SiC alloys prepared via powder metallurgy(Multidisciplinary Digital Publishing Institute, 2017-04-06) Yang, C; Muránsky, O; Zhu, HL; Thorogood, GJ; Avdeev, M; Huang, HF; Zhou, XTA new generation of alloys, which rely on a combination of various strengthening mechanisms, has been developed for application in molten salt nuclear reactors. In the current study, a battery of dispersion and precipitation-strengthened (DPS) NiMo-based alloys containing varying amounts of SiC (0.5–2.5 wt %) were prepared from Ni-Mo-SiC powder mixture via a mechanical alloying (MA) route followed by spark plasma sintering (SPS) and rapid cooling. Neutron Powder Diffraction (NPD), Electron Back Scattering Diffraction (EBSD), and Transmission Electron Microscopy (TEM) were employed in the characterization of the microstructural properties of these in-house prepared NiMo-SiC DPS alloys. The study showed that uniformly-dispersed SiC particles provide dispersion strengthening, the precipitation of nano-scale Ni3Si particles provides precipitation strengthening, and the solid-solution of Mo in the Ni matrix provides solid-solution strengthening. It was further shown that the milling time has significant effects on the microstructural characteristics of these alloys. Increased milling time seems to limit the grain growth of the NiMo matrix by producing well-dispersed Mo2C particles during sintering. The amount of grain boundaries greatly increases the Hall–Petch strengthening, resulting in significantly higher strength in the case of 48-h-milled NiMo-SiC DPS alloys compared with the 8-h-milled alloys. However, it was also shown that the total elongation is considerably reduced in the 48-h-milled NiMo-SiC DPS alloy due to high porosity. The porosity is a result of cold welding of the powder mixture during the extended milling process. © This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
- ItemHelium ion irradiation behavior of Ni-1wt.%SiCNP composite and the effect of ion flux(Elsevier, 2015-12) Zhou, XL; Huang, HF; Xie, R; Thorogood, GJ; Yang, C; Li, ZJ; Xu, HJSilicon carbide nanoparticle-reinforced nickel metal (Ni–SiCNP composite) samples were bombarded by helium ions with fluences of 1 × 1016 and 3 × 1016 ions/cm2 at two different fluxes. The microstructural and mechanical changes were characterized via TEM and nanoindentation. Nano-scaled helium bubbles in the shape of spheres were observed in the samples irradiated at high flux and polygons at low flux. The number of helium bubbles increased with the fluence, whereas their mean size remained unaffected. In addition, the nanohardness of the damage layer also increased as the fluence increased. In addition this study suggests that a higher flux results in a higher number of smaller helium bubbles, while showing no obvious effect on the irradiation-induced hardening of the materials. © 2015 Elsevier B.V
- ItemImpact of pre-existing crystal lattice defects on the accumulation of irradiation-induced damage in a C/C composite(Elsevier, 2022-06) Wang, ZY; Muránsky, O; Zhu, HL; Wei, T; Zhang, Z; Ionescu, M; Yang, C; Davis, J; Hu, G; Monroe, P; Windes, WA carbon-fibre reinforced carbon-matrix (C/C) composite was irradiated with 30 MeV C6+ ions to a peak damage of ∼25 dpa. Ion irradiation-induced microstructural changes were mainly studied using Raman spectroscopy. The irradiation-induced crystal lattice defect accumulation in the C/C composite was compared with a reference of PCIB graphite (nuclear-grade). It shows that a high concentration of pre-existing crystal lattice defects in the studied C/C composite have a significant impact on the unexpectedly high disordering of the crystal lattice observed along the entire ion range. In comparison, PCIB graphite with much less pre-existing crystal lattice defects behaves in a more predictable manner with the irradiation damage accumulated in a narrow high dpa region. We rationalised that a large number of pre-existing crystal lattice defects in the C/C composite lead to a stronger electron-phonon coupling and play an important role on the formation of stable crystal lattice defects due to electronic energy loss during ion irradiation. The present results have implications for the development of C/C composites for radiation-tolerant applications, in terms of the crystal lattice defect elimination in the as-manufactured microstructure. Additionally, this investigation identifies a fundamental knowledge gap in the electronic energy loss effect on the irradiation damage produced in carbon-based materials at intermediate ion energies. © 2022 Elsevier B.V.
- ItemInvestigating bulk mechanical properties on a micro-scale: micro-tensile testing of ultrafine grained Ni–SiC composite to determine its fracture mechanism and strain rate sensitivity(Elsevier, 2020-03-15) Xu, A; Yang, C; Thorogood, GJ; Bhattacharyya, DIn this study, in-situ micro-tensile testing technique was used to investigate the mechanical properties of ultrafine grained Ni-3wt% SiC composite the size effect on the mechanical properties of the ultrafine grained Ni-3wt% SiC composite, and to further reveal the reasons for the low ductility of the bulk Ni-3wt%SiC composite. Dog-bone micro-tensile samples were manufactured using a Focused Ion Beam (FIB) milling machine to 15 μm length with a cross sectional area of 5 μm by 5 μm. The micro-tensile samples are pulled in tension at a quasi-static strain rate of 0.000087/s (LSR) and a relatively faster strain rate of 0.011/s (HSR). Analysis of experimental stress-strain plots for the LSR tests measured yield stress, ultimate tensile stress and modulus values that approach values previously reported for bulk/macro-level tensile tests. However, the elongation and fracture energy at the micro-level is approximately half that at the bulk scale. This discrepancy is attributed to the presence of unwanted carbon and silicon oxide impurities ∼1.5 μm in diameter which act as stress concentrators especially given their large size relative to the width of the tensile specimens. The composition of these impurities was validated by transmission electron microscopy, and they seem to be the most likely cause of low ductility of the Ni-3wt% SiC composite. In all, the study undertaken here was able to replicate mechanical properties observed at the macro scale as well as reproduce a strain rate effect. Furthermore, the failure mode of Ni-3wt% SiC composite was identified and analysed in detail. Crown Copyright © 2019 Published by Elsevier B.V
- ItemInvestigating bulk mechanical properties on a micro-scale: micro-tensile testing of ultrafine grained Ni–SiC composite to determine its fracture mechanism and strain rate sensitivity(The Minerals, Metals & Materials Society, 2020-02-25) Bhattacharyya, D; Xu, A; Yang, C; Thorogood, GJIn this study, in-situ micro-tensile testing technique was used to investigate the mechanical properties of ultrafine grained Ni-3wt% SiC composite the size effect on the mechanical properties of the ultrafine grained Ni-3wt% SiC composite, and to further reveal the reasons for the low ductility of the bulk Ni-3wt%SiC composite. Dog-bone micro-tensile samples were manufactured using a Focused Ion Beam (FIB) milling machine to 15 μm length with a cross sectional area of 5 μm by 5 μm. The micro-tensile samples are pulled in tension at a quasi-static strain rate of 0.000087/s (LSR) and a relatively faster strain rate of 0.011/s (HSR). Analysis of experimental stress-strain plots for the LSR tests measured yield stress, ultimate tensile stress and modulus values that approach values previously reported for bulk/macro-level tensile tests. However, the elongation and fracture energy at the micro-level is approximately half that at the bulk scale. This discrepancy is attributed to the presence of unwanted carbon and silicon oxide impurities ∼1.5 μm in diameter which act as stress concentrators especially given their large size relative to the width of the tensile specimens. The composition of these impurities was validated by transmission electron microscopy, and they seem to be the most likely cause of low ductility of the Ni-3wt% SiC composite. In all, the study undertaken here was able to replicate mechanical properties observed at the macro scale as well as reproduce a strain rate effect. Furthermore, the failure mode of Ni-3wt% SiC composite was identified and analysed in detail.
- ItemOn development of NiMo-SiC alloys via powder metallurgy for the use in molten salt environment(Engineers Australia, 2017-11-27) Yang, C; Muránsky, O; Zhu, HL; Avdeev, M; Huang, HF; Huai, P; Zhou, XTA new generation of alloys, which rely on a combination of various strengthening mechanisms, has been developed for application in molten salt environment, namely in future molten salt reactors (MSR), and concentrating solar power (CSP) plants. In the current study, a battery of NiMo-based alloys containing varying amounts of SiC (0.5-2.5 wt%) were prepared by mechanical alloying from Ni-Mo-SiC powder mixture, The mechanical alloying was followed by spark plasma sintering and rapid cooling. Neutron Powder Diffraction (NPD), Electron Back Scattering Diffraction (EBSD) and Transmission Electron Microscopy (TEM) were employed in the characterization of the microstructural properties of these in-house prepared NiMo-SiC alloys. The present study shows that uniformly-dispersed SiC particles provide dispersion strengthening, the precipitation of nano-scale Ni3Si nano-precipitates provides precipitation strengthening, and the solid-solution of Mo in the Ni matrix provides solid-solution strengthening. In addition, formed Mo2C particles limit the grain growth of NiMo matrix thus further increasing the strength of these NiMo-SiC via Hall-Petch strengthening. As a result, these newly developed NiMo-SiC alloys possess superior strength in comparison to conventional forged NiMo alloys. However, it is shown that the cold welding of powders during the mechanical alloying leads to porosity, which might then lead to reduced ductility.© 2017 Engineers Australia
- ItemOn the origin of strengthening mechanisms in Ni-Mo alloys prepared via powder metallurgy(Elsevier, 2017-01-05) Yang, C; Muránsky, O; Zhu, HL; Thorogood, GJ; Huang, HF; Zhou, XTA new class of materials, which rely on the dispersion strengthening of SiC particles in addition to precipitation strengthening by nano-precipitates is being developed for the application in molten salt nuclear reactors. A battery of dispersion and precipitation strengthened (DPS) NiMo-based alloys containing varying amount of SiC (0.5–2.5 wt.%) was prepared via a mechanical alloying (MA) route followed by spark plasma sintering (SPS), rapid cooling, high-temperature annealing and water quenching. Lab X-ray Diffraction (XRD), Electron Back Scattering Diffraction (EBSD), and Transmission Electron Microscopy (TEM) were employed in the microstructural characterization of this new type of alloys. It is shown that the NiMo matrix of these alloys is effectively reinforced by dispersion of SiC from the initial powder mixture and nano-Ni3Si precipitates, which precipitated during the sintering/annealing process. Furthermore, the matrix is strengthened by solid-solution of Mo in Ni. As a result, these newly developed NiMo alloys take advantage of dispersion, precipitation and solid solution strengthening, which leads to their superior mechanical properties. © 2016 Elsevier Ltd
- ItemSynthesis, structure and conductivity of BaIn0.8Mn0.2O3 − δ(Elsevier, 2014-04-01) Yang, C; Shu, T; Zhang, H; Dong, J; Zhiwen, S; Xiong, C; Sihai, Y; Guobao, L; Liao, F; Lin, JGreen BaIn0.80Mn0.20O2.70 (S1) has been synthesized by solid-state reaction under high temperature, and black BaIn0.80Mn0.20O2.60 (RS1) is obtained by treating S1 under vacuum at 500 °C. They were characterized by powder X-ray and neutron diffraction, selected area electron diffraction, magnetic measurement, and impedance spectrum. S1 and RS1 crystallize in Cmcm (a = 5.9722(3), b = 5.9664(3), c = 8.4511(4) Å) and P21/c (a = 5.9328(7), b = 5.9445(11), c = 16.8154(14) Å, β = 90.02(2)°), respectively. Oxide ion vacancies are confirmed to exist in S1 and RS1 by the neutron diffraction data. © 2014, Elsevier B.V.