Browsing by Author "Buslaps, T"

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    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
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    Elastoplastic deformation and damage process in duplex steel studied using synchrotron and neutron diffraction
    (Scientific.Net, 2017-08-22) Zhao, YC; Joncour, LL; Baczmański, A; François, M; Wroński, S; Panicaud, B; Gadalińska, E; Braham, C; Buslaps, T; Paradowska, AM
    In the present work, the mechanical behavior of phases in duplex steel during tensile test was studied. Special interest was taken in the analysis of damage process just before failure. In this aim two diffraction methods: in-situ time of flight neutron diffraction and X-ray synchrotron diffraction were applied. Using diffraction data, the slip mechanism on crystallographic planes during plastic deformation was investigated. In the case of aged UR45N steel, it was found that significant softening caused by damage process was initiated in the ferritic phase. The lattice strains measured in situ by two above mentioned diffraction methods were compared with prediction of the self-consistent model. © 2021 by Trans Tech Publications Ltd.
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    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.
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    In situ high-energy X-ray diffraction study and quantitative phase analysis in the α+γ phase field of titanium aluminides
    (Elsevier, 2007-12) Yeoh, LA; Liss, KD; Bartels, A; Chladil, HF; Avdeev, M; Clemens, H; Gerling, R; Buslaps, T
    Quantitative atomic structure and phase analysis in the titanium aluminide intermetallic system of composition Ti–45Al–7.5Nb–0.5C (at.%) was conducted in situ by use of high-energy X-ray diffraction from a synchrotron and evaluated using the Rietveld method, implementing a model for atomic order in the α-phase which describes the order to disorder transition α2→α at the eutectoid temperature. The order parameter exhibits unexpected behavior and is entangled with the competition of different kinetic processes. © 2007, Elsevier Ltd.
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    In situ synchrotron high-energy x-ray diffraction analysis on phase transformations in Ti-Al alloys processed by equal-channel angular pressing
    (Wiley-Blackwell, 2009-11) Liss, KD; Whitfield, RE; Xu, W; Buslaps, T; Yeoh, LA; Wu, XL; Zhang, DL; Xia, KN
    Mixtures of 47-Al and 53-Ti powders (atomic %) have been consolidated using back pressure equal-channel angular pressing starting with both raw and ball-milled powders. In situ synchrotron high-energy X-ray diffraction studies are presented with continuous Rietveld analysis obtained upon a heating ramp from 300 K to 1075 K performed after the consolidation process. Initial phase distributions contain all intermetallic compounds of this system except Al, with distribution maxima in the outer regions of the concentrations (α-Ti, TiAl3). Upon annealing, the phase evolution and lattice parameter changes owing to chemical segregation, which is in favour for the more equilibrated phases such as γ-TiAl, α(2)-Ti3Al and TiAl2, were followed unprecedentedly in detail. An initial δ-TiH2 content with a phase transition at about 625 K upon heating created an intermediate β-Ti phase which played an important role in the reaction chain and gradually transformed into the final products. © 2009, Wiley-Blackwell.
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    In-situ characterization of phase transformations and microstructure evolution in a γ-TiAl based alloy
    (The Minerals, Metals & Materials Society (TMS), 2008-06-01) Liss, KD; Bartels, A; Clemens, H; Stark, A; Buslaps, T; Phelan, D; Yeoh, LA
    Phase diagrams and microstructures of titanium aluminides are rather complex and, so far, little data were observed in-situ at elevated temperatures. We report on two-dimensional high energy X-ray diffraction and complementary laser scanning confocal microscopy to characterize the appearing phases and to follow the phase evolution in-situ and in real time. As an example, the microstructure evolution of a quenched γ-TiAl alloy, consisting of α2-Ti3Al grains at room temperature, has been followed in both reciprocal and direct space as a function of temperature up to 1400°C. At 700 – 800°C extremely fine γ-laths are formed in α2-grains occurring through an oriented rearrangement of atoms. Streaks linking reflections of both phases testify from coherent lattice and orientation gradients in the transforming crystallite. At temperatures around the eutectoid temperature recrystallization effects and the γ->α phase transition take place leading to grain refinement.
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    In-situ study of phases and microstructures of titanium aluminides
    (Australian Institute of Physics, 2006-12-04) Liss, KD; Yeoh, LA; Bartels, A; Clemens, H; Phelan, D; Buslaps, T
    The phase diagrams and microstructures of titanium aluminides are rather complex and little or no data were observed during in-situ experiments at elevated temperatures up to 1400 °C, where different processes compete, such as recovery, phase transitions, recrystallization, twinning, crystallite growth, segregation and more. Two-dimensional high energy X-ray diffraction is a powerful method to characterize the phase composition and modern synchrotron sources are strong enough to follow the evolution of the material in real time. Besides texture relations as well as grain and phase correlations, we followed the coherent transition from the alpha to the gamma phase and vice versa. A streak of diffuse scattering appears in reciprocal space bridging reciprocal lattice points of both phases and disappears after the transition completed. This proves, that the phase transition is a well ordered process. Furthermore, the system has been observed in a Laser Scanning Confocal Microscope in situ and in real time, relating the micro structure to the diffraction pattern. Fine laths of the lamellar alpha/gamma grains are created during the phase transition and coarsen as a function of time. The unique combination of the two complementary in-situ techniques was used for the first time and reveals novel, consistent information on a phase transformation in a real solid.
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    Phase fractions, transition and ordering temperatures in TiAl-Nb-Mo alloys: an in- and ex-situ study.
    (Elsevier, 2010-08) Schmoelzer, T; Liss, KD; Zickler, GA; Watson, IJ; Droessler, LM; Wallgram, W; Buslaps, T; Studer, AJ; Clemens, H
    Intermetallic γ-TiAl based alloys of the TNM™ alloy family attain their excellent processing characteristics by a high β-phase content present at hot-working temperatures. Subsequent to hot-working the β-phase content is decreased by a heat treatment step performed at temperatures where the β-phase fraction exhibits a minimum. In this study, in- and ex-situ experiments were conducted on three alloys with different contents of β/β0 stabilizing elements. The course of phase fractions as a function of temperature as well as phase transition temperatures were determined by means of in-situ high-energy X-ray diffraction experiments. Additionally, dynamic scanning calorimetry investigations were performed to obtain complementary data on the transition temperatures. Quantitative metallography was conducted on heat treated and quenched specimens to acquire additional information on the dependence of the phase fractions on temperature. By neutron diffraction experiments the ordering temperatures of the constituent phases were determined. It was shown that the experiments yielded consistent results which differ significantly from ThermoCalc simulations for which a commercial TiAl database was used. The differences between the experimental results and the thermodynamic predictions are discussed. © 2010, Elsevier Ltd.
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    Precipitation, recovery, phase transition and recrystallization processes of massively transformed TiAI scrutinized by ex- and in-situ high-energy X-ray diffraction
    (Australian Institute of Physics, 2005-01-31) Liss, KD; Bystrzanowski, S; Bartels, A; Buslaps, T; Clemens, H; Gerling, R; Schimansky, FP; Stark, A
    High-energy synchrotron radiation above 100 keV is a novel and sophisticated probe to access the volume properties of materials. A Debye-Scherrer method is shortly presented for the measurements of textures, strain and composition. Low density, high specific yield strength, good oxidation resistance and good creep properties at elevated temperatures make intermetallic γ-TiAl-based alloys top candidates as structural materials for advanced jet and automotive engines as well as for future hypersonic vehicles. The mechanical properties depend strongly on composition, thermo mechanical processing and subsequent heat treatments. The present study examines the recrystallization processes of a massively transformed specimen of Ti45AI46Nb9 upon a heat ramp from room temperature to 1400 deg C. The registered Debye-Scherrer rings are rich of features relating to thermal expansion, phase changes, domain and phase coherences, chemical separation and much more which will be regarded in detail.
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    Towards the thermodynamic equilibrium of titanium aluminides after consolidation by back pressure equal channel angular pressing
    (ARC Centre of Excellence for Design in Light, 2007-12) Xu, W; Wu, X; Whitfield, R; Liss, KD; Buslaps, T; Yeoh, LA; Zhang, DL; Xia, K
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    Two dimensional high energy x-ray powder diffraction
    (Australian Institute of Physics, 2006-12-04) Yeoh, LA; Liss, KD; Buslaps, T
    High-energy synchrotron radiation (around 100 keV) combined with a two-dimensional detector boasts the advantage of high penetration power for bulk studies of materials and simple setup geometries. Typically, the diffraction pattern is obtained for a several millimeter thick sample using a transmission geometry setup and the resulting concentric Debye-Scherrer rings are recorded on a flat detector. The radii of the rings and their intensities reflect the structure and phase composition of the sample and the ring morphology can be evaluated, revealing grain statistics. Grain correlations across phase boundaries or domain relations can also be identified and sometimes a local reciprocal lattice of a crystallite can be mapped. Furthermore, anisotropies in intensity and ring radius reveal texture and lattice strain, respectively. Data acquisition times for these patterns range from below a second to few minutes, allowing for in-situ registration during temperature cycles, resulting in a huge amount of individual diffraction patterns which have to be evaluated. As a result, algorithms need to be scripted to automate and batch-process the data evaluation. Currently code is being written in SCILAB, a public available software package, to extract the 1D pattern and other parameters for further analysis with greater efficiency. This method can also be extended to the study of many other processes; such as thermo-mechanical deformation in light metals, like titanium aluminides, magnesium, oxidation layers from steel processing and amorphous materials to mention a few.