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Browsing by Author "Wei, T"

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Atomic 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, HJ
The 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.
A 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, K
Titanium 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.
Corrigendum 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, HJ
The 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.
Crack initiation and crack growth assessment of a high pressure steam chest
(Elsevier, 2011-01) Payten, WM; Wei, T; Snowden, KU; Bendeich, PJ; Law, M; Charman, D
Extensive cracking had occurred in a number of high pressure steam chests. An assessment was undertaken based on the R5 British Energy methodology to assess the components for both creep–fatigue damage initiation and crack growth analysis to determine fitness for purpose. The analysis determined that the remaining base rupture endurance life of the component was greater then 1 million hours, however, due to the start-up and shutdown ramp rates, creep–fatigue damage greater then unity has occurred leading to crack initiation in a number of locations. These cracks were confirmed during internal inspection of the steam chest. A subsequent crack growth analysis determined that the component could safely be returned to service for the expected future life of the station. © 2011, Elsevier Ltd.
Development of ion and neutron irradiation capabilities at ANSTO in structural materials
(Materials Australia and the Australian Ceramic Society, 2018-11-29) Wei, T
Not available
The 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, M
The 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.
Effect 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, AK
Aluminum 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.
The 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, JJ
The 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.
Effect of tellurium (Te4+) irradiation on microstructure and associated irradiation-induced hardening
(IOP Publishing, 2021-04) Huang, HF; Liao, JZ; Lei, GH; Muránsky, O; Wei, T; Ionescu, M
The GH3535 alloy samples were irradiated using 15-MeV Te4+ ions at 650 °C to a dose of 0.5, 3.0, 10, and 20 dpa, respectively. The Te atoms distribution and microstructure evolution were examined by electron probe microanalysis (EPMA) and transmission electron microscopy (TEM). The nano-indenter was then used to measure the nano-hardness changes of samples before and after irradiation. TEM results showed the formation of dislocation loops in the irradiated samples. Their mean diameters increase with the increase of irradiation dose and tends to be saturated when irradiation dose exceeds 10 dpa. The ratio of yield strength increments calculated by dispersed barrier hardening (DBH) model is basically consistent with that of nano-hardness increments measured by nano-indenter. In addition, the relationship between the nano-hardness increments and dpa for the GH3535 alloy irradiated by Te ions has been revealed in the study. © 2021 Chinese Physical Society and IOP Publishing Ltd
Exploring the influence of pH on the structural intricacies of uranium oxide hydrates containing both Cd(ii) and K(i) ions
(Royal Society of Chemistry, 2023-05-28) Ablott, TA; Lu, KT; Wei, T; Zhang, YJ
We report the synthesis of two new dual-cation uranium oxide hydrate (UOH) materials, containing both Cd2+ and K+ ions, along wxrith their characterisation by means of single-crystal X-ray diffraction and a range of other structural and spectroscopic techniques. The materials were found to differ in structures, topology and uranium to cation ratios, with the layered UOH-Cd crystallising in a plate morphology and containing a U : Cd : K ratio of 3 : 1.5 : 1. Conversely, the framework-type UOF-Cd incorporates much less Cd, with a U : Cd : K ratio of 4.4 : 0.2 : 1 and is found as needle-like crystals. A common feature in both structures is the presence of β-U3O8 type layers with a distinct uranium centre which lacks the expected uranyl bonds, highlighting the importance of the β-U3O8 layer in the subsequent self-assembly and preferential formation of a variety of structural types. Most importantly, by exploiting the additional flexibility provided by monovalent cation species (i.e., K+) as secondary metal cations to synthesise these novel dual-cation materials, this work highlights the potential for broadening the scope of viable synthetic UOH phases towards furthering the understanding of these systems in their roles as alteration products in the surrounds of spent nuclear fuel in deep geological repositories. © The Authors - Open Access CC BY Licence
Impact 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, W
A 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.
An investigation of LnUO4 (Ln = Dy and Ho): structures, microstructures, uranium valences and magnetic properties
(Elsevier, 2021-09-12) Lu, KT; Zhang, YJ; Wei, T; Zhang, ZM; Avdeev, M; Zheng, RK
The phase formation, structures, microstructures, uranium valences and magnetic properties of LnUO4 (Ln = Dy and Ho) were investigated. Although sintering of the precursors in argon at 1450 °C for seven days and 1400 °C for six hours both resulted in the desired phase, sintering at higher temperature for longer duration led to the formations of well crystalized lanthanide monouranates with much better homogeneity. Cubic fluorite structures were determined using X-ray diffraction data, which was confirmed with transmission electron microscopy and Raman spectroscopy. The nature of pentavalent uranium was verified with a combination of diffuse reflectance and X-ray photoelectron spectroscopies. The magnetic suseptability measurements revealed that they are paramagnetic with no long-range magnetic orders, likely due to the extensive short-range oxygen defects. Overall the improved structural and spectroscopic understandings of LnUO4 have implications in nuclear materials especially for potential accident tolerance fuels and spent fuel management. Crown Copyright © 2021 Published by Elsevier Ltd.
Irradiation 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, K
A 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.
Materials surveillance program for the OPAL research reactor
(European Nuclear Society, 2007-03-11) Harrison, RP; Carr, DG; Wei, T; Stathers, PA
The OPAL research reactor has recently achieved full power and will begin normal operation in the early part of 2007. One aspect of the design of OPAL has been the inclusion of a surveillance program for the materials used in the reactor core regions. These materials are exposed to a high neutron flux and their properties, such as tensile strength, fracture toughness and physical dimensions (through radiation-induced growth), are expected to change through the life of the reactor. Estimates of these changes have been obtained from literature data and have been accommodated in the design. However, data at the operating temperature of OPAL is limited. In order to guarantee safe operation of these materials, a surveillance program was developed during the detailed design phase of the project. The program involves the placement of miniature samples in high flux regions close to the reactor core. These samples will be removed at intervals and will be subjected to extensive mechanical testing to determine any changes compared with samples in the unirradiated condition. Additional samples will be sectioned from other high-fluence components that will be removed well before the 40 year design life. © The Authors
Microstructural design for thermal creep and radiation damage resistance of titanium aluminide alloys for high-temperature nuclear structural applications
(Elsevier, 2014-10) Zhu, HL; Wei, T; Carr, DG; Harrison, RP; Edwards, L; Seo, DY; Maruyama, K; Dargusch, MS
Microstructure plays an important role in strengthening of metallic materials. Various microstructures can be developed in titanium aluminide (TiAl) alloys, which can enable different combinations of properties for various extreme environments in advanced nuclear systems. In the present paper the mechanisms for microstructural strengthening and the effects of various microstructural features on thermal creep and radiation damage resistance of TiAl alloys are reviewed and compared. On the basis of the results, the evidence-based optimum microstructure for the best combination of thermal creep and radiation damage resistance of TiAl alloys is proposed. The heat treatment processes for manufacturing the optimal microstructure are also discussed. © 2014, Elsevier Ltd.
New methods of mass spectrometry based on an Electron Cyclotron Resonance ion source
(Australian Institute of Physics, 2006-12-05) Hotchkis, MAC; Josh, M; Waring, CL; Wei, T
We are investigating the use of multiply-charged atomic ions for measuring isotopic ratios by mass spectrometry. With multiply-charged ions, molecular interferences are reduced or eliminated, as small molecules generally cannot exist as multiply-charged ions. The Electron Cyclotron Resonance Ion Source (ECRIS) provides a highly efficient means for the production of beams of multiply-charged atomic ions [1]. We have built a compact ECRIS at ANSTO for this work. Applications include the measurement of radiocarbon in small mass samples, as an alternative to Accelerator Mass Spectrometry (AMS). In our method for radiocarbon [3], the same two principles that enable AMS to work are used, but in reverse order. Molecular interferences are eliminated in the first stage of the spectrometer system, by producing high charge state ions directly from an ECRIS. 14N interference is eliminated in the second stage, by converting the beam to negative ions in a charge exchange cell. In another application of the ECRIS, we are using it with a single magnetic sector analyser to determine stable isotopic ratios such as 13C/12C and 18O/16O. Measurements of these and other stable isotopes are widely used in geo- and bio-sciences, where either natural variations are studied or isotopic tracers are used. Conventional isotope ratio mass spectrometers use molecular ions (such as CO2+) to determine such ratios. In our method, 2+ atomic ions are selected, thereby eliminating possible molecular interferences and resolving mass ambiguities that exist with the conventional molecular ion method. [1] R. Geller, Electron Cyclotron Resonance Ion Sources and ECR Plasmas, IOP, Bristol, 1996. [2] R. Middleton, in Proc. First Conf. on Radiocarbon Dating with Accelerators, H.E. Gove (ed.), Rochester, USA, 1978. [3] M.A.C. Hotchkis and T. Wei, 10th International Conference on AMS, Sept 5-10 2005, Berkeley, USA.
Pyrochlore glass‐ceramics fabricated via both sintering and hot isostatic pressing for minor actinide immobilization
(John Wiley & Sons, Inc., 2020-03-19) Zhang, YJ; Zhang, ZM; Wei, T; Kong, L; Kim, YJ; Gregg, DJ
Pyrochlore glass‐ceramics (GCs) have been investigated with samples fabricated via both sintering and hot isostatic pressing (HIPing) of a mixed oxide precursor. It has been demonstrated that sintering at 1200°C in air is necessary to obtain well‐crystallized pyrochlore crystals in a sodium aluminoborosilicate glass through a one‐step controlled cooling. The crystallization, structure, and microstructure of Eu2Ti2O7 pyrochlore as the major phases in residual glass were confirmed with X‐ray diffraction (XRD), scanning electron microscopy‐energy dispersive spectroscopy, transmission electron microscopy, and Raman spectroscopy. The structures of major Eu2Ti2O7 pyrochlore and minor [Eu4.67O(SiO4)3] apatite in both sintered and HIPed samples were refined using synchrotron XRD data. While the processing atmosphere did not appear to affect the cell parameter of the main pyrochlore phase, very small volume expansion (~0.3%) was observed for the minor apatite phase in the HIPed sample. In addition, static leaching of the HIPed sample confirmed that pyrochlore GCs are chemically durable. Overall, pyrochlore GCs prepared via both sintering and HIPing with the Eu partitioning factor of ~23 between ceramics and the residual glass are suitable waste forms for minor actinides with processing chemicals. © 1999-2020 John Wiley & Sons, Inc.
Radiation effects on microstructure and hardness of a titanium aluminide alloy irradiated by helium ions at room and elevated temperatures
(Elsevier B.V., 2015-04) Wei, T; Zhu, HL; Ionescu, M; Dayal, P; Davis, J; Carr, DG; Harrison, RP; Edwards, L
A 45XD TiAl alloy possessing a lamellar microstructure was irradiated using 5MeV helium ions to a fluence of 5×1021ionm−2 (5000appm) with a dose of about 1dpa (displacements per atom). A uniform helium ion stopping damage region about 17μm deep from the target surface was achieved by applying an energy degrading wheel. Radiation damage defects including helium-vacancy clusters and small helium bubbles were found in the microstructure of the samples irradiated at room temperature. With increasing irradiation temperature to 300°C and 500°C helium bubbles were clearly observed in both the α2 and γ phases of the irradiated microstructure. By means of nanoindentation significant irradiation hardening was measured. For the samples irradiated at room temperature the hardness increased from 5.6GPa to 8.5GPa and the irradiation-hardening effect reduced to approximately 8.0GPa for the samples irradiated at 300°C and 500°C. © 2015 Elsevier B.V.
Small punch test of LC4/SiCP metal matrix composites
(Trans Tech Publications, 2010-09-17) Mak, J; Wuhrer, R; Humphries, SR; Booth, N; Heness, G; Yeung, WY; Wei, T; Qin, JN; Ouyang, QB; Zhang, D
There have been growing demands of high performance metal matrix composites in advanced engineering applications in virtue of their high specific strengths. This paper is to report an assessment of the mechanical properties of LC4/SiCp metal matrix composites using an innovative testing technique, small punch test. The composite materials of this study were produced by stir casting method with particulate reinforcements of 7wt.% and 14wt.% of SiC respectively. Small punch testing was performed on the LC4 base alloy and the two composites materials. The small punch test is a relatively new mechanical testing technique capable of utilizing small disk-shaped samples to determine the mechanical properties of the test materials. In this study, the equivalent fracture strain, εqf of the LC4/SiCp MMCs was characterised and compared with the base alloy. The fracture mechanism of the test samples was examined using scanning electron microscopy. © Trans Tech Publications Ltd.
A solution for estimating the tensile yield strength from small specimens
(ASTM Compass, 2013-05-24) Mak, J; Wei, T; Wuhrer, R; Yeung, WY; Heness, G; Zhang, D
The small punch test is an innovative test that utilises small disc-shaped specimens to assess the mechanical behaviour of materials. The main advantage is the relatively small specimen size. In this article, a modified analytical solution for the small punch maximum bend strength is proposed that is based on classical plate theory. A clear linear relationship is observed between the tensile yield strength σYS and the small punch maximum bend strength σy for both alloys and metal matrix composites. © ASTM International.

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