Browsing by Author "Carr, DG"
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- ItemCombined in situ neutron diffraction and acoustic emission of twin nucleation & twin growth in extruded ZM20 Mg alloy(Trans Tech Publications, 2009-11-10) Muránsky, O; Barnett, MR; Carr, DG; Vogel, SC; Oliver, ECIn the present work in situ neutron diffraction and acoustic emission were used concurrently to study deformation twinning in two ZM20 Mg alloys with significantly different grain sizes at room temperature. The combination of these techniques allows differentionation between the twin nucleation and the twin growth mechanisms. It is shown, that yielding and immediate post-yielding plasticity in compression is governed primarily by twin nucleation, whereas the plasticity at higher strains is governed by twin growth. The current results further suggest that yielding by twinning happens in a slightly different manner in the fine-grained as compared to the coarse-grained alloy. © Trans Tech Publications Ltd
- 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.
- ItemDefect dynamics in polycrystalline zirconium alloy probed in situ by primary extinction of neutron diffraction(American Institute Physics, 2013-02-13) Kabra, S; Yan, K; Carr, DG; Harrison, RP; Dippenaar, RJ; Reid, M; Liss, KDAfter alpha+beta-zirconium has fully transformed into beta-phase upon heating, the intensities of all beta-Zr Bragg reflections decrease simultaneously as a function of time. It is shown that this effect represents a transition from the kinematic to the dynamic theory of diffraction due to the ever increasing crystal perfection driven by thermal recovery of the system. The best fitting coherent crystallite size of 30 mu m and other microstructural features are verified by in situ laser scanning confocal microscopy. This effect of primary extinction in neutron diffraction has been employed to further investigate the crystal perfection kinetics. Upon further heating, crystal recovery is identified as a process of dislocation annihilation, suffering from lattice friction. Upon cooling, precipitating alpha-Zr induces strain into the perfect beta-crystallites, re-establishing the kinematic diffraction intensities. An Avrami analysis leads to the estimations of nucleation time, consumption of nucleation sites and lower-dimensional growth. Such technique bears great value for further investigation on all metal systems annealed close to the melting temperature. © 2013, American Institute of Physics.
- ItemDeformation mechanisms of twinning-induced plasticity steels: in situ synchrotron characterization and modeling(Elsevier, 2010-03) Yan, K; Carr, DG; Callaghan, MD; Liss, KD; Li, HJThe plastic deformation behavior of twinning-induced plasticity steels of composition Fe-25Mn-3Si-3Al are investigated by means of in situ synchrotron high-energy X-ray diffraction and compared to self-consistent simulations. It is the first time the alternating interaction of {1 1 1} <1 1 0> slip and {1 1 1} <1 1 2> twinning have been directly observed in situ while undergoing uniaxial tension. The deformation texture is determined mainly by dislocation gliding, while deformation twinning impedes the reinforcement of texture. © 2010, Elsevier Ltd.
- ItemEffect of double ion implantation and irradiation by Ar and He ions on nano-indentation hardness of metallic alloys(Elsevier, 2013-07-01) Dayal, P; Bhattacharyya, D; Mook, WM; Fu, EG; Wang, YQ; Carr, DG; Anderogluc, O; Mara, NA; Misra, A; Harrison, RP; Edwards, LIn this study, the authors have investigated the combined effect of a double layer of implantation on four different metallic alloys, ODS steel MA957, Zircaloy-4, Ti–6Al–4V titanium alloy and stainless steel 316, by ions of two different species – He and Ar – on the hardening of the surface as measured by nano-indentation. The data was collected for a large number of indentations using the Continuous Stiffness Method or “CSM” mode, applying the indents on the implanted surface. Careful analysis of the data in the present investigations show that the relative hardening due to individual implantation layers can be used to obtain an estimate of the relative hardening effect of a combination of two separate implanted layers of two different species. This combined hardness was found to lie between the square root of the sum of the squares of individual hardening effects, (ΔHA2 + ΔHB2)0.5 as the lower limit and the sum of the individual hardening effects, (ΔHA + ΔHB) as the upper limit, within errors, for all depths measured.© 2013, Elsevier B.V.
- ItemEffect of welding thermal cycle on the microstructure of Zircaloy-4(International Institute of Welding, 2009-07-16) Thorogood, KJ; Li, HJ; Carr, DG; Harrison, RP; Nolan, DZirconium and its alloys are important materials commonly utilised in the nuclear industry, primarily due to their low neutron absorption cross-section and excellent corrosion resistant properties. Zircaloy-4 is one of the most widely used nuclear grade zirconium alloys and contains primary alloying elements of tin, iron, chromium and oxygen. Typical applications include structural core components and fuel cladding. Fully welded structures such as heavy water reflector vessels have been fabricated from Zircaloy-4. Although the structure-property relationships of Zircaloy-4 parent metal and weld metal is well understood, there is limited understanding of the same relationship for the narrow weld heat-affected zone. The work reported in this paper is an investigation of the influence of the weld thermal cycles on the microstructure and texture of Zircaloy-4 heat-affected zone material. Discrete regions within the heat-affected zone were simulated using a thermo-mechanical simulator (Gleeble 3500). Peak temperatures of the thermal cycles studied were 1000,1200, 1400 and 1600°C. Weld simulation has been shown to produce a volume of material sufficient for analysis and which represents the individual sub-zones. © 2010, International Institute of Welding
- ItemIn situ neutron diffraction investigation of deformation twinning and pseudoelastic-like behaviour of extruded AZ31 magnesium alloy(Elsevier, 2009-06) Muránsky, O; Carr, DG; Šittner, P; Oliver, ECIn situ neutron diffraction has been used to investigate the deformation twinning and untwinning during cyclic uniaxial straining of hydrostatically extruded AZ31 magnesium alloy. The development of the internal stresses and microstructure in the polycrystalline alloy when twinning takes place is explained on the basis of the two pairs of parent {10.0}||, {11.0}|| and twin {00.2}||, {10.3}|| grain families. The experimentally observed pseudoelastic-like behaviour in stress–strain cycles is interpreted as being due to the activation of reversal twinning processes during loading–unloading cycles. It is proposed that the driving force for the observed untwinning is the existence of high tensile stresses in favourably oriented grains which result from significant twinning activity prior to unloading from the peak stress. © 2009, Elsevier Ltd.
- ItemIn-situ characterization of lattice structure evolution during phase transformation of Zr-2.5Nb(Wiley-Blackwell, 2011-09-01) Yan, K; Carr, DG; Kabra, S; Reid, M; Studer, AJ; Harrison, RP; Dippenaar, RJ; Liss, KDThe alpha-beta phase transformation behavior of Zr-2.5Nb (in mass%) has been characterized in real time during an in situ neutron diffraction experiment. The Zr-2.5Nb material in the current study consists, at room temperature, of alpha-Zr phase (hcp) and two beta phases (bcc), a Nb rich beta-Nb phase and retained, Zr rich, beta-Zr(Nb) phase. It is suggested that this is related to a quench off the equilibrium solubility of Nb atoms in the Zr bcc unit cells. Vegard's law combined with thermal expansion is applied to calculate the composition of the beta-phase, which is compared with the phase diagram, revealing the system's kinetic behavior for approaching equilibrium. © 2011, Wiley-Blackwell.
- ItemInvestigation of deformation twinning in a fine-grained and coarse-grained ZM20 Mg alloy: combined in situ neutron diffraction and acoustic emission(Elsevier, 2010-03) Muránsky, O; Barnett, MR; Carr, DG; Vogel, SC; Oliver, ECNeutron diffraction and acoustic emission were used in a single in situ experiment in order to study the deformation twinning of two ZM20 Mg alloys with significantly different grain sizes at room temperature. The combination of these two techniques facilitates the distinction between twin nucleation and twin growth. It is shown that yielding and immediate post-yielding plasticity in compression along the extrusion direction is governed primarily by twin nucleation, whereas plasticity at higher strains is presumably governed by twin growth and dislocation slip. It is further shown that, in the fine-grained alloy, collaborative twin nucleation in many grains dominates yielding, whereas twin nucleation in the coarse-grained alloy is progressive and occurs over a larger strain range. In addition, it is shown that, despite twin nucleation stresses increasing with decreasing grain size, roughly the same overall volume fraction of twins is formed in both fine and coarse parent grains. This confirms the difficulty of the alternative deformation modes and suggests a negligible suppressive effect of grain size on twinning in the case of the strongly textured fine-grained alloy. The current results also show that twins in the coarse-grained alloy are born less relaxed with respect to surrounding polycrystalline aggregate than those in the fine-grained alloy. This is believed to lead to lower reversal stresses acting on twin grains in the coarse-grained alloy upon unloading and thus to less untwinning and thus to a smaller pseudoelastic-like hysteresis. © 2010, Elsevier Ltd.
- 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.
- ItemMartensitic phase transformation and deformation behavior of Fe–Mn–C–Al twinning-induced plasticity steel during high-pressure torsion(Wiley Online Library, 2014-02-05) Yan, K; Bhattacharyya, D; Lian, Q; Kabra, S; Kawasaki, M; Carr, DG; Callaghan, MD; Avdeev, M; Li, HJ; Wang, Y; Liao, XZ; Langdon, TG; Liss, KD; Dippenaar, RJThe transformation between the face centered cubic austenitic and hexagonal close-packed martensitic phases during high-pressure torsion processing was observed in a Fe–Mn–C–Al twinning-induced plasticity steel. This phase transformation was not found in the same material processed by unidirectional compressive and tensile deformation. Initiated by the high-pressure loading, the martensite phase initially increased with torsional strain but diminished subsequently. Texture evolution of the austenitic phase was compared with the ideal texture distribution of face-centered cubic materials after shear deformation.© 2014, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- ItemMaterials surveillance program for the OPAL research reactor(European Nuclear Society, 2007-03-11) Harrison, RP; Carr, DG; Wei, T; Stathers, PAThe 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
- ItemMeasurement of fracture toughness of hydrided Zircaloy - 4.(The Institute of Materials Engineering Australasia Ltd., 2004) Callaghan, MD; Yeung, WY; Ripley, MI; Carr, DGZircaloy-4 is a zirconium alloy that will be used for construction of many of the core components in the replacement research reactor at Lucas Heights. The fracture toughness of the alloy and its radiation-induced reduction over the 40 year planned life of the reactor is an important mechanical property for this application. This study aims to simulate the radiation-induced reduction in fracture toughness by hydriding Zircaloy-4. A range of fracture toughnesses is required to calibrate the sub-size Charpy and small punch (SP) surveillance specimens that will be irradiated over the life of the reactor against standard J1C fracture toughness specimens. Pieces of Zircaloy-4 plate were hydrided in a vessel at a temperature of 520°C, at different pressures for either 10 or 22 hours. Final hydrogen concentrations between 25 wt% ppm and 380 wt% ppm hydrogen were obtained under gaseous atmosphere. The fracture toughness of the hydrided Zircaloy-4 was assessed using sub-size 2.5 mm-thick Charpy, three-point bend J1C and SP tests. The results were correlated to determine the relationship between the J-integral fracture toughness, Charpy impact energy and equivalent fracture strain (εqf) from the SP tests. It was found that as hydrogen concentration and hydride formation increased, the fracture toughness of the alloy generally decreased. The results show there to be a useful relationship between fracture toughness and εqf measured for the SP tests.
- ItemMicrostructural 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, MSMicrostructure 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.
- ItemOptimisation of mixed hardening material constitutive models for weld residual stress simulation using the NeT task group 1 single bead on plate benchmark problem.(American Society of Mechanical Engineers (ASME), 2009-07-26) Smith, MC; Nadri, B; Smith, AC; Carr, DG; Bendeich, PJ; Edwards, LA single weld bead deposited on a flat plate is a deceptively simple problem that is in practice a challenge for both measurement and prediction of weld residual stresses. Task Group 1 of the NeT collaborative network has examined this problem in an extensive programme of measurement and simulation extending from 2002 to 2008. As a result, the NeT bead on plate forms an ideal benchmark problem for the development of weld residual stress simulation techniques. One of the conclusions of NeT Task Group 1 is that the most accurate predictions of weld residual stresses in austenitic steels are achieved using mixed isotropic-kinematic material constitutive models. However, the use of these models can require both extensive materials data, and compromises in fitting either the monotonic or cyclic responses. This paper reports a detailed matrix of sensitivity studies aimed at optimising the behaviour of mixed hardening models in welding simulation, using the Lemaitre-Chaboche formulation in the ABAQUS finite element code. Predicted stresses and strains in the NeT bead on plate specimen are compared with the extensive database of residual stress measurements. Further studies examine sensitivity to the handling of high temperature inelastic strains, using a novel two-stage annealing functionality implemented within ABAQUS. The results show that, overall, the most accurate predictions are made if the Lemaitre-Chaboche parameters are optimised to fit the monotonic response over the first 2% of plastic strain. However, further improvements in prediction could be achieved if the constitutive model were capable of independently fitting both the monotonic and saturated cyclic response of the material.
- ItemRadiation 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, LA 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.
- ItemRadiation-induced growth in zircaloy-4(International Group On Research Reactors, 2005-09-12) Harrison, RP; Carr, DG; Kim, YS; Boccanera, L; Ripley, MI; Stathers, PA; Humphries, SRNot available
- ItemSensitivity of predicted weld residual stresses in the NeT task group 1 single bead on plate benchmark problem to finite element mesh design and heat source characteristics(American Society of Mechanical Engineers (ASME), 2009-07-26) Bendeich, PJ; Smith, MC; Carr, DG; Edwards, LA single weld bead deposited on a flat plate is a deceptively simple problem that is, in practice, a significant challenge for both measurement and prediction of weld residual stresses. Task Group 1 of the NeT collaborative network has examined this problem in an extensive programme of measurement and simulation extending from 2002 to 2008. Thus, the NeT bead on plate forms an ideal benchmark problem for the development of weld residual stress simulation techniques. It is often difficult to separate the influence of different analysis variables in a large collaborative study such as NeT Task Group 1. This paper examines sensitivity to mesh design, element type, and heat source characteristics in a closely controlled study using several different mesh designs, element types (both tetrahedral and hexahedral), and heat sources, but the same material constitutive model and finite element analysis code. It complements a companion paper that varies material constitutive models. A dedicated heat source modelling tool with a semi-automatic interface to the ABAQUS finite element code has been used to vary the heat source characteristics, thus facilitating rapid and controlled sensitivity studies without the need for bespoke heat source coding within ABAQUS.
- ItemStructural integrity verification of a primary circuit pump flywheel for the OPAL Research Reactor(International Group On Research Reactors, 2005-09-12) Carr, DG; Harrison, RP; Payten, WMThe flywheels on nuclear reactor coolant pump motors provide inertia to ensure a slow decrease in coolant flow in the event of loss of power; thus preventing fuel damage due to the reduced coolant flow. During operation at normal speed, a flywheel has sufficient kinetic energy to produce high-energy missiles and excessive vibration of the coolant pump assembly if the flywheel should fail. The structural integrity of a large steel flywheel to be used in the primary cooling circuit of the OPAL research reactor at Lucas Heights was evaluated according to the requirements of the US Nuclear Regulatory Commission guide RG 1.14. This guide was developed for nuclear power plants where significant over-speeds in pumps are possible. In the OPAL reactor at ANSTO such pump over-speeds are not possible, however, the code was used to demonstrate the incredibility of failure of the flywheel and consequently a guillotine failure of the primary cooling system pipework.
- ItemStructural integrity verification of a primary circuit pump flywheel for the OPAL Research Reactor(Insitute of Materials Engineering Australasia Ltd, 2006) Carr, DG; Harrison, RP; Payten, WMThe flywheels on nuclear reactor coolant pump motors provide inertia to ensure a slow decrease in coolant flow in the event of loss of power; thus preventing possible fuel damage due to the reduced coolant flow. During operation at normal speed, a flywheel has sufficient kinetic energy to produce high-energy missiles and excessive vibration of the coolant pump assembly if the flywheel should fail. It is thus important to evaluate the fracture properties of the material to ensure it can withstand the applied stress. The structural integrity of a large steel flywheel to be used in the primary cooling system of the OPAL research reactor at Lucas Heights was evaluated according to the requirements of the US Nuclear Regulatory Commission guide RG 1.14. The guide was developed for nuclear power plants where significant over-speeds in pumps are possible. In the OPAL reactor at ANSTO such pump over-speeds are not possible, however, the code was used to demonstrate the incredibility of failure of the flywheel. An experimental program determined the fracture toughness and tensile properties of the flywheel material; thick section AS 3678 Grade 350 plate. Revision 4 of the well-validated British Energy R6 defect assessment procedure was used to analyse the critical speed and crack length for the flywheel using the two-component failure assessment diagram which considers brittle fracture and plastic collapse. The results of the evaluation are presented in this paper, and illustrate what can be accomplished through the application of modern methods of integrity assessment.