Browsing by Author "Yan, K"

Now showing 1 - 18 of 18
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    Defect 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, KD
    After 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.
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    Deformation mechanisms of twinning-induced plasticity steels: in situ synchrotron characterization and modeling
    (Elsevier, 2010-03) Yan, K; Carr, DG; Callaghan, MD; Liss, KD; Li, HJ
    The 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.
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    Direct, time-resolved in-situ observation of dynamic recyrstallization and related phenomena in the bulk of zirconium alloy
    (Australian Institute of Physics, 2009-02-04) Liss, KD; Garbe, U; Schambron, T; Almer, JD; Li, HJ; Yan, K; Dippenaar, RJ
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    Dynamic recovery and recrystallization during hot-working in an advanced TiAl alloy
    (Carl Hanser Verlag, 2011-01-01) Schmoelzer, T; Liss, KD; Rester, M; Yan, K; Stark, A; Reid, M; Peel, MJ; Clemens, H
    Intermetallic TiAl alloys are light-weight high-temperature materials and intended to partly replace Ni based alloys in jet engines. Due to difficult forming operations, component prices are high and limit the possible field of application. During hot-working, recovery and recrystallization effects determine the microstructural evolution and thereby the mechanical properties of the finished part as well as its behavior during deformation. To study the occurring experiments with high-energy X-rays were conducted. By means of this method, the dominating processes were identified. The results were validated through electron back scatter diffraction experiments. © 2011 CARL HANSER VERLAG
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    From single grains to texture
    (Wiley-VCH Verlag GmbH & Co. KGaA, 2009-10) Yan, K; Liss, KD; Garbe, U; Daniels, JE; Kirstein, O; Li, HJ; Dippenaar, RJ
    Structural materials, such as metals, ceramics, and their composites are most often polycrystalline. The nature, morphology, and composition of their microstructure determine in large measure the mechanical properties of the final product, and the art to design novel materials is to find particular arrangements which make them harder, more shock absorbing, heat resistant, or self-recovering upon damage and aging. The understanding of the basic processes and their interplay in a polycrystalline structure are most important for improved simulation of plastic deformation and to predict their thermo-mechanical behavior. © 2009, Wiley-VCH Verlag GmbH & Co. KGaA
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    From the single grain to texture
    (Australian Institute of Physics, 2009-02-06) Yan, K
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    In situ observation of dynamic recrystallization in the bulk of zirconium alloy
    (Wiley-VCH Verlag Berlin, 2009-08) Liss, KD; Garbe, U; Li, HJ; Schambron, T; Almer, JD; Yan, K
    Dynamic recrystallization and related effects have been followed in situ and in real time while a metal undergoes rapid thermo-mechanical processing. Statistics and orientation correlations of embedded/bulk material grains were deduced from two-dimensional X-ray diffraction patterns and give deep insight into the formation of the microstructure. Applications are relevant in materials design, simulation, and in geological systems. © 2009, Wiley-VCH Verlag Berlin
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    In situ study of dynamic recrystallization and hot deformation behavior of a multiphase titanium aluminide alloy
    (American Institute of Physics, 2009-12-01) Liss, KD; Schmoelzer, T; Yan, K; Reid, M; Peel, MJ; Dippenaar, RJ; Clemens, H
    Hot-compression tests were conducted in a high-energy synchrotron x-ray beam to study in situ and in real time microstructural changes in the bulk of a beta-solidifying titanium aluminide alloy. The occupancy and spottiness of the diffraction rings have been evaluated in order to access grain growth and refinement, orientation relationships, subgrain formation, dynamic recovery, and dynamic recrystallization, as well as phase transformations. This method has been applied to an alloy consisting of two coexisting phases at high temperature and it was found that the bcc beta-phase recrystallizes dynamically, much faster than the hcp alpha-phase, which deforms predominantly through crystallographic slip underpinned by a dynamic recovery process with only a small component of dynamic recrystallization. The two phases deform to a very large extent independently from each other. The rapid recrystallization dynamics of the beta-phase combined with the easy and isotropic slip characteristics of the bcc structure explain the excellent deformation behavior of the material, while the presence of two phases effectively suppresses grain growth. © 2009, American Institute of Physics
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    In-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, KD
    The 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.
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    Martensitic 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, RJ
    The 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.
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    On the atomic anisotropy of thermal expansion in bulk metallic glass
    (Wiley-Blackwell, 2011-09-01) Qu, DD; Liss, KD; Yan, K; Reid, M; Almer, JD; Wang, Y; Liao, XZ; Shen, J
    Glass transition temperature and plastic yield strength are known to be correlated in metallic glasses. We have observed by in situ synchrotron high energy X-ray diffraction anisotropy of the thermal expansion behavior in the nearest neighbor and second nearest neighbor atomic distances in the building blocks of Zr-Cu-Ni-Al based bulk metallic glass, leading inevitably to shear. Mechanical yielding of the latter on the atomic scale leads to the glass transition and the increase of the free volume. These experimental results uncover the mechanism, how glass transition and yield strength are linked. © 2011, Wiley-Blackwell.
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    On the compression behavior of an austenitic Fe-18Mn-0.6C-1.5Al twinning-induced plasticity steel
    (Wiley, 2013-06-20) Peng, CT; Callaghan, MD; Li, HJ; Yan, K; Liss, KD; Ngo, TD; Mendis, PA; Choi, CH
    High manganese austenitic TWIP steels are of great potential in the field of transportation-related industries owing to their exceptional combination of strength and ductility. A series of compression experiments were conducted on a Fe–18Mn–0.6C–1.5Al alloy at various strain rates (from 1.0 × 10−2 to 6.4 × 103 s−1) and total strains (≈15 and ≈20%) with a Gleeble 3500 thermo-mechanical simulator and a Split Hopkinson Pressure Bar system. Under compressive deformation, results showed this alloy possessed excellent strain-hardening behavior, attributed to the occurrence of mechanical twinning during deformation. The prevailing deformation mechanism was observed to be twinning, which was substantiated by microstructural analyses, as well as phase identification and evolution of crystallographic texture. Copyright © 1999-2020 John Wiley & Sons, Inc.
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    Phase transition and ordering behavior of ternary Ti-Al-Mo alloys using in-situ neutron diffraction
    (HANSER eLibrary, 2011-06-01) Kabra, S; Yan, K; Mayer, S; Schmoelzer, T; Reid, M; Dippenaar, RJ; Clemens, H; Liss, KD
    Neutron diffraction has been used for in-situ. investigations to elucidate the phase transformation behavior of two Mo-containing TiAl alloys with compositions of Ti-44Al-3Mo and Ti-44Al-7Mo (in at.%). Five different phases are present in these alloys. These include three ordered phases at room temperature, namely alpha(2), beta(0) and gamma and two disordered phases, alpha and beta, which occur at higher temperatures. The sequence of the three phase transformations in each alloy has been determined. The phase transformation and disordering/ordering temperatures were determined on heating and cooling from the diffracted peak intensities. The neutron experiments are particularly sensitive to the order disorder transitions in TiAl alloys, which are compared with the overall phase fractions obtained from previous high energy X-ray diffraction. Hysteresis and undercooling effects are observed for the various phase transformations and depend on the nature of atomic rearrangements. © 2011 Carl Hanser Verlag GmbH & Co. KG
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    Physical thermo-mechanical simulation of magnesium: an in-situ diffraction study
    (Elsevier, 2014-04-17) Liss, KD; Yan, K; Reid, M
    Time-resolved, two-dimensional synchrotron high-energy X-ray diffraction has been utilized for the in-situ investigation of the microstructural evolution of magnesium, during heating and during plastic deformation at various temperatures. Throughout static heating of the as-extruded material, first recovery, then recrystallization and finally grain growth occurred with increasing temperature. Grain rotation was observed during grain growth of the static heated samples. Subsequent plastic deformation, through compression, at lower temperatures revealed the activated deformation systems. At room temperature, extension-twinning flips the crystallite orientations abruptly from the extrusion to the compression fiber texture. In contrast, at elevated temperatures, twinning is negligible and the texture reorientation progresses in a gradual steady-state flow regime, ending in a tilted basal texture with a tilt angle depending on the degree of deformation. The methodology described herein offers parametric studies related to microstructural and deformation processes in an unprecedented way. © 2014, Published by Elsevier B.V.
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    Specimen-size dependency and modelling of energy evolution during high-temperature low-cycle fatigue of pressure vessel steel
    (Elsevier Ltd., 2011-08-01) Callaghan, MD; Humphries, SR; Law, M; Ho, M; Yan, K; Yeung, WY
    High-temperature low-cycle fatigue testing was conducted on pressure vessel steel using standard and miniature specimen sizes and the fatigue toughness required for macrocrack propagation was investigated. A definite specimen-size dependency was observed for both the threshold cumulative plastic strain energy and cycles required for macrocrack propagation, which was explained to be influenced by geometric conditions. An analytical modelling prediction was developed that accounted for specimen-size dependency and was successfully applied to predict fatigue toughness to macrocrack propagation. (C) 2011 Acta Materialia Inc.
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    Structural origins for the high plasticity of a Zr-Cu-Ni-Al bulk metallic glass
    (Pergamon-Elsevier Science Ltd, 2012-09-11) Qu, DD; Liss, KD; Sun, YJ; Reid, M; Almer, JD; Yan, K; Wang, Y; Liao, XZ; Shen, J
    The structural origins for the high plasticity of a Zr(53)Cu(18.7)Ni(12)Al(16.3) (at.%) bulk metallic glass are explored. Under plastic flow conditions, in situ synchrotron high-energy X-ray diffraction reveals that the atomic strain saturates to the closest packing in the longitudinal direction of the applied load while atoms yield in the transverse plane. Scanning electron microscopy investigation reveals that global plasticity benefits from abundant shear band multiplication and interactions. Atomic level flows are seen to accompany profuse shear bands. The plasticity enhancement of this metallic glass benefits from such atomic level flows. Atomic level flow facilitates the activation of shear transformation zones that further self-assemble to promote shear band multiplication. On the other hand, it also mitigates the shear band propagation that prevents catastrophic shear band extension. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. © 2012, Elsevier Ltd.
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    Thermo-mechanical processing in a synchrotron beam
    (Elsevier, 2010-11-25) Liss, KD; Yan, K
    Well collimated, high energy X-rays of 90 keV from synchrotron sources have been used to study metals undergoing plastic deformation in situ, in real time and in the bulk of the materials. The spottiness of the Debye–Scherrer rings, showing reflections from individual crystallites, is analyzed to obtain grain statistics, mosaic spread and grain orientation. Upon cold deformation, coarse grained materials show fingerprints of subgrain formation, grain rotation, grain refinement and the evolution from a single grain into the asymptotic texture. Lattice strain, its partition and anisotropy can be simultaneously revealed. Heating of metals under continuous load drives the observation through the regimes of phase transformation and grain relationships therein, grain coarsening, dynamic recovery and dynamic recrystallization. Examples on copper, magnesium, twinning induced plasticity steel, zirconium alloy and titanium aluminium intermetallics are shown. © 2010, Elsevier Ltd.
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    Variability of poisson's ratio and enhanced ductility in amorphous metal
    (Wilye-V C H Verlag GMBH, 2013-05-01) Liss, KD; Qu, DD; Yan, K; Reid, M
    Ductile bulk metallic glass of composition 53.0Zr–18.7Cu–12.0Ni–16.3Al (at%) is plastically deformed under uniaxial compression and observed in situ by synchrotron high-energy X-ray diffraction. The diffraction patterns reveal the induced atomic strain is orientation dependent. At the onset of plastic deformation, the atomic strain in the compression direction saturates to a close-nearest-neighbor distance while atoms relax in the transverse direction. The ever increasing transverse atomic strain expresses in an augmentation of the apparent Poisson's ratio up to ν = 0.5, which is consistent with volume conservation. Contradicting phenomena from linear mechanics, such as the non-vanishing shear modulus at ν = 0.5 can be explained by the non-affine character of the deformation, giving rise to characteristics of a localized martensitic phase transformation. The findings explain the often-reported phenomena such as, the high Poisson's ratio values found in metallic glasses, the partially liquid character of the structure, the free volume increase and the Bauschinger effect. © 2013, Wiley-VCH Verlag GmbH & Co. KGaA