Browsing by Author "Phelan, D"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- ItemDirectional 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, LAMaking 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
- ItemIn-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, LAPhase 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.
- ItemIn-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, TThe 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.