Browsing by Author "Zhou, XT"
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- 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/).
- ItemMolten FLiNaK salt infiltration into degassed nuclear graphite under inert gas pressure(Elsevier B.V., 2015-04-01) He, ZT; Gao, L; Qi, W; Zhang, BL; Wang, X; Song, JL; He, XJ; Zhang, C; Tang, H; Holmes, R; Xia, HH; Zhou, XTInfiltration of molten FLiNaK salt into degassed nuclear graphite samples under inert gas pressure was studied. The weight gain of different grades (2020, 2114, IG-110, NBG-8, G1 and G2) of nuclear graphite during infiltration with different pressures was measured. Molten salt infiltration was compared with mercury intrusion porosimetry where it was found that mercury infiltration was a useful predictor of the threshold pressure and infiltration volume per gram graphite for molten salt infiltration. The distribution and morphology of salt in the graphite were observed by scanning electron microscopy, with very little difference between the molten salt content at the center and edge of samples for samples infiltrated at pressure higher than the threshold pressure. Increased molten salt infiltration with increased pressure resulted from the occupation of smaller pores and full occupation of the larger irregular pores. The similarity of weight gain between molten salt infiltration equilibrated at 20 and 100 h showed 20 h was adequate to obtain equilibrium. © 2014 Elsevier Ltd.
- 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