Browsing by Author "Zhu, HL"
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- ItemAtomic origins of radiation-induced defects and interfacial strengthening in additively manufactured titanium aluminide alloy irradiated with Kr-ions at elevated temperature(Elsevier, 2019-04-04) Zhu, HL; Qin, MJ; Aughterson, RD; Wei, T; Lumpkin, GR; Ma, Y; Li, HJThe irradiation microstructure of the additively manufactured titanium aluminide (TiAl) alloy subjected to in situ transmission electron microscope (TEM) irradiation with 1 MeV Kr ions at the elevated temperature of 873K was investigated. Triangle and large hexagon shaped volume defects were observed within the γ-TiAl phase in the TEM images of the irradiated microstructure. High resolution TEM images and composition analyses revealed the volume defects were vacancy-type stacking fault tetrahedrals (SFTs). Molecular dynamic simulations showed that the increased diffusion coefficient at the elevated temperature promoted the movement and aggregation of vacancies, leading to the formation and growth of SFTs in the irradiated FCC γ phase. The lamellar interfaces in the irradiation microstructure were more effective for acting as strong sinks to absorb the primary point defects and defect clusters at the elevated temperature. The initial defects at the interfaces of the additively manufactured TiAl alloy enhanced the sink strength of the material and greatly refined SFTs near the lamellar interfaces. © 2019, The Authors.
- ItemThe characterisation and formation of novel microstructural features in a Ti−Nb−Zr−Mo−Sn alloy manufactured by Laser Engineered Net Shaping (LENS)(Elsevier, 2021-01) Zhu, HL; Wang, ZY; Muránsky, O; Davis, J; Yu, S; Kent, D; Wang, G; Dargusch, MSNovel microstructural features were found in the Ti−Nb−Zr−Mo−Sn alloy manufactured by Laser Engineered Net Shaping (LENS). Examination of the microstructure showed that the fabricated sample exhibits a layered morphology with arced deposit boundaries. Novel distributions and morphologies of various phases including β, α, α'' and ω were detected in the LENS-manufactured part which substantially differ to conventionally processed alloy counterparts. The β grains and subgrains spread over multiple deposits and layers, aligned to the build direction, forming a complex network microstructure comprising large highly textured columnar grains aligned to β phase <001> orientations. The α precipitates have needle-like shapes and are widely distributed across a majority of the deposited layers, whereas the nanoscale ω particles were present in regions absent of α precipitation. Localised, massively transformed α'' phase with a very long and curved rod-like shape and substantial surface defects was identified. The formation of these novel microstructural features is investigated and discussed in the context of the characteristics of the LENS fabrication process. The microstructures are attributed to the complex thermal history in the unique deposit-by-deposit and layer-by-layer method employed during LENS additive manufacturing in conjunction with the complex precipitation behaviours exhibited by TiNb-based alloys. The characteristics and formation mechanisms of the LENS-manufactured Ti−Nb−Zr−Mo−Sn alloy microstructures revealed here provide a basis to optimize LENS and post-LENS heat treatment processes to optimize microstructures for improved performance. © 2020 Elsevier B.V
- ItemA comparison of microstructural strengthening for thermal creep and radiation damage resistance of titanium aluminide alloys(Elsevier, 2013-07-01) Zhu, HL; Wei, T; Carr, DG; Harrison, RP; Edwards, L; Seo, DY; Maruyama, KTitanium aluminide (TiAl) alloys were initially developed for moderate temperature (600–850 °C) applications in the aerospace and automotive industries because they have high specific strength, low density, good corrosion, oxidation and creep resistance at elevated temperatures [1]. TiAl alloys have also received much attention as potential candidate materials for high temperature nuclear structural applications because of excellent radiation resistance and low neutron activation [2], [3], [4] and [5]. Moreover, the microstructure of TiAl alloys can be developed to be more complex than the up-to-now reported microstructures of other advanced structural materials. Various microstructures allow different combinations of properties for various extreme environments in advanced nuclear systems. The effects of microstructural features on creep behaviour of TiAl alloys have been intensively investigated over the last two decades [6], [7] and [8]. However, the effects of microstructural features on irradiation behaviour of TiAl alloys have rarely been studied. In the present short note, the microstructural strengthening for thermal creep and irradiation damage of TiAl alloys is compared. This provides useful guidance for further experiment work necessary to understand the irradiation behaviour of TiAl alloys. © 2013, Elsevier B.V.
- ItemCorrigendum to ‘Atomic origins of radiation-induced defects and the role of lamellar Interfaces in radiation damage of titanium aluminide alloy irradiated with Kr-ions at elevated temperature’ [Acta Mater. 172 (2019) 72–83](Elsevier, 2020-09-15) Zhu, HL; Qin, MJ; Aughterson, RD; Wei, T; Lumpkin, GR; Ma, Y; Li, HJThe authors regret that the scale bars in Figure 8(c) BF-STEM and 8(d) HAADF-STEM for volume defects near the γ/γ lamellar interfaces in the Kr-ion irradiated microstructure of the TiAl alloy irradiated at 873 K are mislabelled. The authors would like to apologise for any inconvenience caused. © 2020 Acta Materialia Inc. Published by Elsevier Ltd.
- 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.
- ItemDepth control of ferromagnetism in FePt3 films by ion-irradiation(International Conference on Neutron Scattering, 2017-07-12) Causer, GL; Cortie, DL; Zhu, HL; Ionescu, M; Mankey, GJ; Klose, FThe roadmap which outlines storage technology of magnetic hard disk drives predicts storage densities above 5 Tb/in2 to be realised by isolated, individually addressable ferromagnetic (FM) bits of <10 nm in lateral dimension. In principle, artificially patterned structures of this type can be manufactured by x-ray, ion-and electron-beam lithography. However, there may be alternative solutions for obtaining these regular, nanoscale patterns of isolated FM dots. Our proposal is to locally transform a non-magnetic layer into a pattern of geometrically defined FM islands. Such a phase transition could be initiated by locally changing some physical parameter of the layer, such as its strain state or chemical composition leading to ferromagnetism. Here, we present a chemical order (paramagnetic) to chemical disorder (FM) phase transition stimulated by He+ irradiation of a FePt3 thin film. This talk will present preliminary work focussing on depth profiling the ion-beam induced FM order. By controlling the energy (15 keV) and fluence (2x1016 ions/cm2) of the ion-beam, we show ferromagnetism can be locally induced into the upper-half volume of the initially chemically well-ordered 280 nm FePt3 film. Polarised neutron reflectometry was used to investigate the depth dependence of the layer averaged ion-beam induced FM moment within the thin film. Data analysis of the Kiessig fringes observed in the reflectivity post-irradiation suggest the FM / nonmagnetic interface is atomically sharp. The resulting bilayer structure was found to be homogenous in chemical composition but heterogeneous in both chemical and magnetic orders.
- ItemDepth-profiling magnetic interfaces formed intrinsically in FePt3 by ion-beams(American Physical Society, 2018-03-07) Causer, GL; Cortie, DL; Zhu, HL; Ionescu, M; Mankey, GJ; Wang, XL; Klose, FUsing ion-beams to locally modify material properties is rapidly gaining momentum as a technique of choice for the fabrication of magnetic nano-elements because the method provides the capability to nano-engineer in 3D, which is important for many future spintronic technologies. The precise definition of the resulting element shape is crucial for device functionality. In this work, the intrinsic sharpness of a magnetic interface formed by nano-machining FePt3 films using He+ irradiation is investigated. Through careful selection of the irradiating ion’s energy and fluence, ferromagnetism is locally induced into a fractional volume of a paramagnetic (PM) FePt3 film by modifying the chemical order parameter. Using a combination of magnetometry, transmission electron microscopy and polarised neutron reflectometry it is demonstrated that the interface over which the PM to ferromagnetic modulation occurs is confined to a few atomic monolayers only. Using density functional theory, the mechanism for the ion-beam induced magnetic transition is elucidated and shown to be caused by an intermixing of Fe and Pt atoms in anti-site defects above a threshold density.
- ItemThe effect of applied stress on the high-temperature creep behaviour and microstructure of NiMoCr Hastelloy-N® alloy(Elsevier, 2021-05) Zhu, HL; Muránsky, O; Wei, T; Davis, J; Budzakoska-Testone, E; Huang, HF; Drew, MThe high-temperature creep behaviour and microstructural evolution of Hastelloy-N® was investigated using miniaturised creep samples tested under vacuum at 973 K (700 °C) and stresses of 100 MPa and 165 MPa. The higher applied stress reduced the creep life of the alloy sevenfold, and the creep mechanism at 165 MPa was predominately dislocation-creep while the creep mechanism at 100 MPa was a combination of dislocation creep, diffusion creep and grain boundary sliding. The post-creep microstructure examination using Electron Back-Scatter Diffraction (EBSD) technique showed significantly larger number of Low-Angle Grain Boundaries (LAGBs) and Geometrically-Necessary Dislocations (GNDs) formed during creep at 165 MPa than at 100 MPa. On the other hand, the microstructure of the sample tested at 100 MPa revealed more pronounced precipitation of secondary carbides along High-Angle Grain Boundaries (HAGBs) due to the longer exposure to high temperature. The precipitation of secondary carbides along grain boundaries resulted in grain boundary embrittlement and the promotion of intergranular cracking, which then resulted in low strain-to-failure in the low-stress creep test sample. In addition, it is shown that the prolonged exposure to the elevated temperature lead to Cr depletion from the matrix, reducing solid solution strengthening during creep. © 2021 Acta Materialia Inc. Published by Elsevier B.V.
- ItemEffect of extrusion profile on surface microstructure and appearance of aluminum extrusions with different Fe contents(Springer, 2013-02-21) Zhu, HL; Wei, T; Couper, MJ; Dahle, AKAluminum alloy extrusions with variations in profiles and Fe-rich particles were produced using different extrusion dies and iron contents. A microstructural examination of the extrusion surface shows that the extrusion profile and iron content have a great effect on the size and number of Fe-rich particles, grain size, texture, and fraction of high-angle grain boundaries due to varying localized plastic deformation and temperature in the extrudate. After etching and anodizing, surface imperfections such as grain boundary grooves that influence the final surface appearance are formed on the extrusion surfaces. The severity of grain boundary grooves is found to be directly linked to the number of Fe-rich particles. Hence, the extrusion profile has a dramatic influence on surface imperfections and the appearance of the final anodized extrusions through its effect on the surface microstructure. © 2013, TMS.
- ItemThe effect of microstructure and welding-induced plasticity on the strength of Ni–Mo–Cr alloy welds(Elsevier, 2021-06) Danon, AE; Muránsky, O; Zhu, HL; Wei, T; Flores-Johnson, EA; Li, ZJ; Kruzic, JJThe mechanical performance of a Ni–Mo–Cr (GH3535) alloy weldment, produced using a matching filler metal, was assessed and compared to the surrounding parent metal. Ambient-temperature mechanical characterisation included hardness testing, small punch testing and uniaxial tensile testing, while a crystal plasticity finite element model was used to assess the impact of crystallographic texture on the mechanical properties. Despite the similar chemical composition, the weld metal exhibited superior strength and ductility to that of the parent metal. The higher strength was primarily attributed to the high dislocation density in the weld metal imbued by the welding-induced thermo-mechanical loading. In contrast, the ductility difference was attributed to M6C carbide stringers in the parent metal that initiated fracture at lower strains when compared to the weld metal, with the latter containing finer, well-dispersed M6C carbides. © 2021 Acta Materialia Inc. Published by Elsevier B.V.
- 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/).
- ItemEffects 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, HJPost-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.
- ItemEtching behavior of aluminum alloy extrusions(SpringerLink, 2014-10-16) Zhu, HLThe etching treatment is an important process step in influencing the surface quality of anodized aluminum alloy extrusions. The aim of etching is to produce a homogeneously matte surface. However, in the etching process, further surface imperfections can be generated on the extrusion surface due to uneven materials loss from different microstructural components. These surface imperfections formed prior to anodizing can significantly influence the surface quality of the final anodized extrusion products. In this article, various factors that influence the materials loss during alkaline etching of aluminum alloy extrusions are investigated. The influencing variables considered include etching process parameters, Fe-rich particles, Mg-Si precipitates, and extrusion profiles. This study provides a basis for improving the surface quality in industrial extrusion products by optimizing various process parameters. © 2014, The Minerals, Metals & Materials Society.
- ItemFormation of streak defects on anodized aluminum extrusions.(Springer, 2010-05) Zhu, HL; Zhang, XQ; Couper, MJ; Dahle, AKStreaking is a common surface defect on anodized extrusions of 6xxx series soft alloys. Very often, the defects only become apparent after anodizing, which makes it difficult to identify their root cause. In industry practice, a trial-and-error method has been taken to reduce the intensities of the streak defects, greatly increasing the fabrication cost. This paper describes the formation mechanism of various streak defects on the basis of a literature review and experimental results. This provides a basis for developing effective measures for preventing the formation of these defects for the extrusion industry. © 2010, Springer. The original publication is available at www.springerlink.com
- ItemHigh-temperature corrosion of helium ion-irradiated Ni-based alloy in fluoride molten salt(Elsevier, 2015-02-01) Zhu, HL; Holmes, R; Hanley, TL; Davis, J; Short, KT; Edwards, LA comparison of the effect of helium-ion-radiation damage on a Ni–Mo–Cr–Fe alloy exposed to high-temperature (750 °C) corrosion in eutectic LiF–NaF–KF molten salt has been made. Microstructural examination showed that both the corroded-only and irradiated and corroded samples exhibit the characteristics of intergranular corrosion. However, helium ion irradiation introduces defects such as helium bubbles and cavities into the microstructure, greatly increasing intragranular corrosion of the irradiated sample. The thickness of the remaining corrosion zone for the irradiated sample was much greater than that for the unirradiated sample. © 2014 Elsevier Ltd.
- 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.
- ItemIrradiation behaviour of α2 and γ phases in He ion implanted titanium aluminide alloy(Elsevier, 2014-07-01) Zhu, HL; Wei, T; Blackford, MG; Short, KT; Carr, DG; Harrison, RP; Edwards, L; Seo, DY; Maruyama, KA Ti–45Al–2Nb–2Mn + 0.8 vol.% TiB2 (at.%) alloy with fully lamellar microstructure consisting of hexagonal-close-packed (hcp) α2 and face-centred-tetragonal (fct) γ phases was irradiated by implanting helium ions to different fluences. Microstructural examination showed that helium cavities are formed in both the α2 and γ phases after He-ion irradiation. However, the helium cavities and their size change with fluence are much larger in the α2 phase than those in the γ phase, indicating that the γ phase exhibits better tolerance to the He-ion irradiation than the α2 phase. Since α2 and γ phases have different crystal structures, they possess differences in helium solubility and interstitial migration. These differences are responsible for the variation in radiation damage behaviour between the two phases. © 2014, Elsevier Ltd.
- ItemLow 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, HJThe 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
- ItemMagnetic interface phenomena in nano-architectures and their applications(Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-19) Causer, GL; Cortie, DL; Zhu, HL; Kostylev, M; Ionescu, M; Mankey, GJ; Wang, XL; Klose, FInterfaces between heterostructure components in nanoscale films play important roles in communicating low-dimensional phenomena and act as anchor points for the direct control and tunability of device performance. In this talk I will give an overview of our group’s recent investigations into the occurrence of magnetic interface phenomena in low-dimensional thin-film systems which have conceivable utility in future condensed-matter technologies. First, the magnetic interface quality of an FePt3 nano-magnet formed via ion-induced chemical disorder will be analysed [1]. Here, neutron and electron measurements used in combination with density functional theory calculations reveal a rather counterintuitive result which could prove beneficial towards the development of ultra-high density magnetic recording devices. In a second study, the layer-averaged static magnetisation and macroscopic magneto-dynamic behaviours of a Co/Pd bilayer during hydrogen-gas cycling are analysed. To perform this characterisation, we first had to develop and commission an original sample environment which innovatively combines polarised neutron reflectometry and microwave spectroscopy [2]. The Co/Pd interface is found to feature tailorable magnetic surface anisotropy in the presence of hydrogen gas – the mechanism of which could act as a safety switch in next-generation vehicles powered by hydrogen.
- ItemMicrostructural 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, HJA 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.