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Browsing by Author "Liss, KD"

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Anisotropy in the thermal expansion of uranium silicide measured by neutron diffraction
(Elsevier, 2018-09) Obbard, EG; Johnson, KD; Burr, PA; Lopes, DA; Liss, KD; Griffiths, GJ; Scales, N; Middleburgh, SC
In-situ neutron diffraction patterns were collected for a sample of as-cast U3Si2 during heating to 1600 °C. Anomalous changes were observed above 1000 °C, including the formation of a new diffraction peak not belonging to P4/mbm U3Si2, unequal changes in the peak intensities and onset of anisotropic lattice expansion. The large data-set enabled derivation of a function-fitted isotropic thermal expansion coefficient to high precision, in close agreement with previous dilatometry results but reducing linearly with temperature over the studied interval. Anisotropy in the instantaneous lattice thermal expansion corresponded to anomalies reported by White et al. (2015) at a similar temperature. © Elsevier B.V
Charge-order melting in charge-disproportionated perovskite CeCu3Fe4O12
(Americal Chemical Society, 2014-10-21) Yamada, I; Etani, H; Hayashi, N; Mizumaki, M; Ueda, S; Abe, H; Liss, KD; Studer, AJ; Ozaki, T; Mori, S; Takahashi, R; Irifune, T
A novel quadruple perovskite oxide CeCu3Fe4O12 has been synthesized under high-pressure and high-temperature conditions of 15 GPa and 1473 K. (57)Fe Mössbauer spectroscopy displays a charge disproportionation transition of 4Fe(3.5+) → 3Fe(3+) + Fe(5+) below ∼270 K, whereas hard X-ray photoemission and soft X-ray absorption spectroscopy measurements confirm that the Ce and Cu valences are retained at approximately +4 and +2, respectively, over the entire temperature range measured. Electron and X-ray diffraction studies reveal that the body-centered cubic symmetry (space group Im3̅, No. 204) is retained at temperatures as low as 100 K, indicating the absence of any types of charge-ordering in the charge-disproportionated CeCu3Fe4O12 phase. The magnetic susceptibility and neutron powder diffraction data illustrate that the antiferromagnetic ordering of Fe ions is predominant in the charge-disproportionated CeCu3Fe4O12 phase. These findings suggest that CeCu3Fe4O12 undergoes a new type of electronic phase in the ACu3Fe4O12 series and that the melting of the charge-ordering in CeCu3Fe4O12 is caused by the substantial decrease in the Fe valence and the resulting large deviation from the ideal abundance ratio of Fe(3+):Fe(5+) = 1:1 for rock-salt-type charge-ordering. © 2014, American Chemical Society.
The contribution of high-energy x-rays and neutrons to characterization and development of intermetallic titanium aluminides
(Wiley-Blackwell, 2011-08-01) Schmoelzer, T; Liss, KD; Staron, P; Mayer, S; Clemens, H
Abstract Intermetallic γ-TiAl based alloys are a novel class of lightweight structural materials that exhibit excellent high-temperature strength while having low density. These properties make them ideal candidates for replacing dense Ni base alloys currently used in the temperature range from 550 to 750 °C. Therefore, extensive research activities were conducted during the last 20 years to make this innovative class of materials fit for service. In this task, diffraction methods have been an important tool for promoting the development of TiAl alloys. The ability to perform experiments in situ and to determine phase fractions even in cases where two phases are present in ultrafine lamellar structures are only two examples for applications in which diffraction methods are indispensable. In this work, a review is given concerning the use of diffraction methods in the development of TiAl alloys. Different methods are introduced and highlighted by examples. This review lists the advantages of diffraction experiments and critically discusses the limits of the individual methods.© 2011, Wiley-Blackwell.
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.
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.
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
Not available
Directional atomic rearrangements during transformations between the α- and γ- phases in titanium aluminides
(Wiley-VCH Verlag Berlin, 2008-04) Liss, KD; Stark, A; Bartels, A; Clemens, H; Buslaps, T; Phelan, D; Yeoh, LA
Making movies in-situ at glowing temperatures up to 1300°C through a microscope (false color image) and from two-dimensional X-ray diffraction (movie frames) reveal the lattice correlations, gradients and intermediate structures during phase transformations in titanium aluminide. A quenched, α2-rich γ-based TiAl first approaches its equilibrium by α2 → γ on a heating ramp, disorders α2 → α and then evolves reversely γ → α, which are morphologically different processes. © 2008, Wiley-VCH Verlag Berlin
Do Q!
(Australian Institute of Physics, 2009-02-05) Liss, KD
Why bother with reciprocal space, if my instrument measures just the diffraction angle? What is behind the synonyms of Reciprocal Space, Q-space, K-space, G-space, Momentum Space and why is it important? X-ray and neutron powder diffraction patterns can be displayed as a function of many independent quantities, such as scattering angle 2θ, lattice spacing d, neutron time of flight τ, energy E, wavelength λ, wave vector k, radius R on a 2-dimensional diffraction image and so on. In most of the cases, experimentalists plot data just against the independent quantity in which their instrument operates without thinking further. This has been escalated with the tradition of X-ray measurements on Cu-Kα tubes to the extreme, that whole evaluation programs work in 2θ only and powder diffraction databases even store patterns in 2θ of Cu-Kα, the profile matching programs re-calculating patterns measured at different wavelengths to this scale. Beamlines at the world's brightest synchrotron sources have been built on Cu-Kα energies for this reason and only slowly, after ten years of the operation of such facilities, the community realizes that other wavelengths may be of advantage. At the end of the chain peer referees and journal editors have become reluctant to authors presenting on this arbitrary scale. So why bother ? - Because: • reciprocal space is the NATURAL space diffraction takes place; • reciprocal space is LINEAR and symmetries can be identified by eye; • the representation directly reflects crystal SYMMETRY; • the representation is INDEPENDENT of the instrument geometry and type of radiation (electrons, neutrons, X-rays, light, atoms...) • the representation is INDEPENDENT of the wavelength used; presentations and publications would become directly COMPARABLE; reciprocal space is WIDELY USED outside the powder diffraction community; modern instruments with 2D detectors DO NOT WORK in 2θ space; The contribution will point out these issues and animate for a lively discussion.
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
ECHIDNA - getting OPAL’s high resolution powder diffractometer into operation
(Australian Institute of Physics, 2006-12-05) Liss, KD; Hunter, BA; Hagen, ME; Noakes, TJ
A new powder diffractometer aiming for high angular and thus high reciprocal space resolution is being constructed within the Neutron Beam Instrumentation Project at the upcoming Australian Neutron Source OPAL near Sydney. The expected neutron flux at the sample can be expected more than 107 n/s. With an array of 128 position sensitive detectors, each equipped with a 30 cm high Söller collimator of 5 arc min acceptance this instrument will range below the highest performances of its kind. In addition to classical applications in powder diffraction, the quasi two-dimensional detector will be used for rapid texture measurements where high separation of peaks is necessary. Even single crystal reciprocal space mapping will be envisaged [1]. The poster compiles an overview of the installation and commissioning of the new instrument. Neutrons are planned to be available from August 2006 and first experimental data be available for the conference. [1] K.-D. Liss, B. Hunter, M. Hagen, T. Noakes, S. Kennedy: "ECHIDNA - The new high-resolution powder diffractometer being built at OPAL", Physica B, accepted (2006)
Echidna—the new high-resolution powder diffractometer being built at OPAL
(The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Liss, KD; Hunter, BA; Hagen, ME; Noakes, TJ; Kennedy, SJ
A new powder diffractometer, named Echidna, aiming for high angular and thus high reciprocal space resolution is being constructed within the Neutron Beam Instrumentation Project at the upcoming Australian Neutron Source OPAL near Sydney. The neutron flux at the sample can be expected to be more than 107 n/s. With an array of 128 position sensitive detectors, each equipped with a 30 cm high Soeller collimator of 5 arc min acceptance this instrument will have one of the highest performances of its kind. In addition to classical applications in powder diffraction, the quasi two-dimensional detector will be used for rapid texture measurements where high separation of peaks is necessary. Even single crystal reciprocal space mapping will be envisaged. The poster compiles an overview of the design, status of the project and potential research to be achieved. © The Authors
Echidna—the new high-resolution powder diffractometer being built at OPAL
(Elsevier B. V., 2006-11-15) Liss, KD; Hunter, BA; Hagen, ME; Noakes, TJ; Kennedy, SJ
A new powder diffractometer aiming for high angular, and thus high reciprocal space, resolution is being constructed within the Neutron Beam Instrumentation Project at the upcoming Australian Neutron Source OPAL, near Sydney. The neutron flux at the sample can be expected to be up to 107 n/cm2/s. With an array of 128 position sensitive detectors, each equipped with a 30 cm high Söller collimator of 5 arc min acceptance this instrument will have one of the highest performances of its kind. In addition to classical applications in powder diffraction, the quasi two-dimensional detector will be used for rapid texture measurements, where high separation of peaks is necessary. Even single crystal reciprocal space mapping is envisaged. The article compiles an overview of the design, status of the project and potential research activities. Crown Copyright © 2006 Published by Elsevier B.V
Evolution of composition and grain correlations upon phase transitions and micro-structural rearrangement processes followed in-situ by high energy x-ray diffraction
(Materials Australia, 2007-07-03) Liss, KD; Yeoh, LA; Clemens, H; Chladil, HF; Bartels, A; Stark, A; Buslaps, T
Two-dimensional powder diffraction using high-energy synchrotron x-rays is a powerful tool for bulk studies of materials and a short introduction of its advantages is given here.
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
Growth of bainitic ferrite and carbon partitioning during the early stages of bainite transformation in a 2 mass% silicon steel studied by in situ neutron diffraction, TEM and APT
(International Union of Crystallography, 2016-01-08) Timokhina, IB; Liss, KD; Raabe, D; Rakha, K; Beladi, H; Xiong, XY; Hodgson, PD
In situ neutron diffraction, transmission electron microscopy (TEM) and atom probe tomography (APT) have been used to study the early stages of bainite transformation in a 2 mass% Si nano-bainitic steel. It was observed that carbon redistribution between the bainitic ferrite and retained austenite at the early stages of the bainite transformation at low isothermal holding occurred in the following sequence: (i) formation of bainitic ferrite nuclei within carbon-depleted regions immediately after the beginning of isothermal treatment; (ii) carbon partitioning immediately after the formation of bainitic ferrite nuclei but substantial carbon diffusion only after 33 min of bainite isothermal holding; (iii) formation of the carbon-enriched remaining austenite in the vicinity of bainitic laths at the beginning of the transformation; (iv) segregation of carbon to the dislocations near the austenite/ferrite interface; and (v) homogeneous redistribution of carbon within the remaining austenite with the progress of the transformation and with the formation of bainitic ferrite colonies. Bainitic ferrite nucleated at internal defects or bainite/austenite interfaces as well as at the prior austenite grain boundary. Bainitic ferrite has been observed in the form of an individual layer, a colony of layers and a layer with sideplates at the early stages of transformation. Copyright © International Union of Crystallography
High energy synchrotron x-rays: a tool for bulk investigations in physics and materials science
(Australian Institute of Physics, 2005-01-31) Liss, KD
High energy X-rays between 30 keV and 1 MeV, as provided by modern synchrotron sources like the ESRF and HASYLAB at DESY, bear the advantage of deep penetration into most materials. Even heavy element compositions can be accessed in their volume. The range of applications is huge and spreads from nuclear physics to the characterization of a metal deformation under industry-related conditions. This presentation compiles an overview of my experience with the most common instrumental techniques and selected applications. Triple axis diffractometry can be used for highest resolution purposes on single crystal characterization, even under heavy and dense sample environments. Thus artificial or ultrasonic superlattices can be characterized as well as structural changes around different kinds of phase transitions. Time resolved studies can be performed stroboscopically from a sub-nanosecond to a second time scale and are presented. Modern two-dimensional detectors are used to obtain rapid overviews in reciprocal space. Whole sets of Debye-Scherrer rings are registered onto the detector, their diameters and eccentricities or their intensity distribution along the rings relating to anisotropic strain or texture measurements, respectively. Imaging techniques such as topography, radiography and computed tomography allow to seize direct information in real space. Combinations of the different techniques will play a most important issue in the design of future beamlines and a flux estimate for a potential Australian beamline is given.
Hydrostatic compression behavior and high-pressure stabilized β-phase in γ-based titanium aluminide intermetallics
(Multidisciplinary Digital Publishing Institute, 2016-07-15) Liss, KD; Funakoshi, K; Dippenaar, RJ; Higo, Y; Shiro, A; Reid, M; Suzuki, H; Shobu, T; Akita, K
Titanium aluminides find application in modern light-weight, high-temperature turbines, such as aircraft engines, but suffer from poor plasticity during manufacturing and processing. Huge forging presses enable materials processing in the 10-GPa range, and hence, it is necessary to investigate the phase diagrams of candidate materials under these extreme conditions. Here, we report on an in situ synchrotron X-ray diffraction study in a large-volume press of a modern (α2 + γ) two-phase material, Ti-45Al-7.5Nb-0.25C, under pressures up to 9.6 GPa and temperatures up to 1686 K. At room temperature, the volume response to pressure is accommodated by the transformation γ → α2, rather than volumetric strain, expressed by the apparently high bulk moduli of both constituent phases. Crystallographic aspects, specifically lattice strain and atomic order, are discussed in detail. It is interesting to note that this transformation takes place despite an increase in atomic volume, which is due to the high ordering energy of γ. Upon heating under high pressure, both the eutectoid and γ-solvus transition temperatures are elevated, and a third, cubic β-phase is stabilized above 1350 K. Earlier research has shown that this β-phase is very ductile during plastic deformation, essential in near-conventional forging processes. Here, we were able to identify an ideal processing window for near-conventional forging, while the presence of the detrimental β-phase is not present under operating conditions. Novel processing routes can be defined from these findings. © 2016, The Authors
In and ex situ investigations of the β-phase in a Nb and Mo containing gamma-TiAl based alloy.
(Elsevier, 2008-06) Clemens, H; Chladil, HF; Wallgram, W; Zickler, GA; Gerling, R; Liss, KD; Kremmer, S; Guther, V; Smarsly, W
In β-stabilized Ti-43Al-4Nb-1Mo-0.1B alloy (composition in atomic percent) the correlation between the occurrence of β-phase and temperature was analyzed experimentally and compared to thermodynamic calculations. Results from in situ high-energy X-ray diffraction, texture measurements, heat treatments, scanning electron microscopy, and temperature-dependent flow stress measurements were used to study the evolution of the β-phase with temperature. Thermodynamic calculations based on the CALPHAD method were applied to correlate the phases developed in the β-solidifying TiAl based alloy under investigation. This alloy is characterized by an adjustable β-phase volume fraction at temperatures where hot-work processes such as forging and rolling are conducted. Due to a high volume fraction of β-phase at elevated temperatures the hot-extruded alloy can be forged under near conventional conditions. © 2008, Elsevier Ltd.
In situ characterization of a Nb and Mo containing γ-TiAl based alloy using neutron diffraction and high-temperature microscopy
(Wiley-VCH Verlag Berlin, 2009-11) Watson, IJ; Liss, KD; Clemens, H; Wallgram, W; Schmoelzer, T; Hansen, TC; Reid, M
In recent times, novel titanium aluminides containing the bcc β-phase at high temperatures are being developed for improved hot-working capabilities, however, predictions of the phase diagrams are merely uncertain. Here we present in-situ neutron studies, which are particularly sensitive to the atomic disorder in the ordered phases. Complementary laser scanning confocal microscopy is employed for in-situ microstructural investigations. © 2009, Wiley-VCH Verlag Berlin
In situ diffraction experiments for the investigation of phase fractions and ordering temperatures in Ti-44 at% Al-(3-7) at% mo alloys
(Wiley, 2011-04-01) Schmoelzer, T; Mayer, S; Sailer, C; Haupt, F; Guther, V; Staron, P; Liss, KD; Clemens, H
Being a strong beta stabilizer, Mo has gained importance as an alloying element for so-called beta/gamma-TiAl alloys. Intermetallic TiAl-based alloys which contain a significant volume fraction of the body-centered cubic beta-phase at elevated temperatures have proven to exhibit good processing characteristics during hot-working. Unfortunately, the effect of Mo on the appearing phases and their temperature dependence is not well known. In this work, sections of the Ti-Al-Mo ternary phase diagram derived from thermodynamic calculations as well as experimental data are presented. The phase transition temperatures stated in these phase diagrams are compared with the results of high-temperature diffraction studies using high-energy synchrotron radiation. Additionally, the disordering temperature of the beta(o)-phase is determined. © 1999-2020 John Wiley & Sons, Inc.

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