Browsing by Author "Li, X"
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- ItemDynamical mechanism of phase transitions in a-site ferroelectric relaxor (Na1/2Bi1/2)TiO3(Australian Institute of Physics, 2016-02-02) Deng, GC; Danilkin, SA; Imperia, P; Li, X; Zhao, XB; Luo, HQ
- ItemIn-situ diffraction studies related to thermo-mechanical processes in metals and alloys(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Liss, KD; Li, X; Dippenaar, RJBoth neutron and synchrotron high-energy X-rays have penetrating power into metals, and intensities are competitive for ex- and in-situ studies of thermo-mechanical processes. They bear great potential in order to speed up materials design by orders of magnitude. The present contribution will enhance novel pioneering experiments on selected metal systems and showcase the complementarity between neutrons and X-rays and to other in-situ techniques, such as the Laser Confocal Scanning Microscope. Neutrons bear the advantage of averaging over larger volumes and therefore, are less dependent on grain statistics, leading to good, quantitative phase analysis and texture measurements. Phase evolutions are studied upon application of high temperature and high pressure. The neutron contrast, different to X-rays has been employed to investigate order-disorder transitions in titanium-aluminides. Moreover, dynamical theory of diffraction leads to the study of the smallest distortions and their kinetics at high temperature in zirconium and titanium alloys. Synchrotron X-rays allow t focusing on a small number of crystallites, showing up traces of grain evolution in reciprocal space, such as grain rotation, grain growth, phase correlations, dynamic recovery and decrystallization such as in a Materials Oscilloscope.
- ItemIn-situ studies of γ-based Ti-Al alloys using synchrotron x-ray and neutron diffraction(Australian Institute of Physics, 2017-02-02) Li, X; Liss, KD; Dippenaar, RJBecause of their low density, good strength, corrosion resistance and high service temperature γ-based titanium aluminides are being considered as materials of choice in the aerospace and automobile industry. In our study, we focus on a series of interesting γ-based Ti-Al alloys with respect to the lattice evolution of Ti-45Al-7.5Nb-0.25C (at. %) during heating under a pressure of 10 GPa followed by synchrotron radiation; order-disorder transitions and shortrange-order in polysynthetic twinned Ti-Al single crystals using neutron scattering and phase transformation and texture evolution of high pressure torsion samples of Ti-45Al-7.5Nb by using complementary X-ray and neutron diffraction. Lattice parameter evolution can be separated into four contributions: thermal expansion, composition, order parameter and pressure. Diffuse scattering at reciprocal lattice positions provides evidence of short-range order, even in the disordered phase at very high temperature. Structural and atomic disorder is largely introduced by severe plastic deformation. These findings are fundamental to develop an improved understanding of the complex phase transformations. We report our first results of experiments performed under extremely high-pressure, relevant to advanced manufacturing processes.
- ItemNeutron and x-ray studies of TiAl-Nb intermetallics undergone high-pressure torsion(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Li, X; Dippenaar, RJ; Kawasaki, M; Liss, KDHigh-pressure torsion is a severe-plastic-deformation technique rendering the bulk metallic material into an ultrafine microstructure. Not only the application of high pressure in the 6 GPa range bears potential for phase transformation, moreover huge plastic shear strains of 10 to 100 is achieved by torsion processing. In a first study, pellets of y-based Ti-45Al-7.5Nb have been processed under 6 GPa at room temperature, (i) with pressure loading and unloading only, (ii) with 5 turns of torsion and (ii) 10 turns. The material, which usually is brittle and hard to deform, was successfully processed and showed ductility under these conditions. First investigations by neutron and X-ray diffraction are presented, emphasizing the complementarity of both kinds of quantum beams. While X-rays determine the overall structure, such as close-packing, neutrons are particularly sensitive to the order parameter in the constituting y-TiAl and a2-Ti3Al intermetallic phases. It is found that the atomic order decreases on larger amount of processing. Also structural transformations regarding the atomic packing take place. These preliminary examinations open routes for physical understanding and recovery of the occurring crystallographic transformation and microstructural arrangements.
- ItemSmall angle neutron scattering on critical polymer clusters formed with tetra-armed prepolymers(International Conference on Neutron Scattering, 2017-07-12) Li, X; Hirosawa, K; Sakai, T; Gilbert, EP; Shibayama, MSol-gel transition is one of phenomena classified to percolation transition. Percolation has been extensively investigated in 1970s – 1990s both experimentally and theoretically. By tuning the concentrations and ratio of monomers and crosslinkers, one can synthesize various critical clusters on the verge of percolation. However, most of the previous studies only focused on one critical conditions (one monomer concentration and one crosslinker ratio). Recently, we succeeded in preparation of critical polymer clusters by cross-end-coupling multi-arm prepolymers, which shows less side-reactions and generates critical polymer clusters with good reproducibility. In this presentation, we revisit this old problem by using well-tuned polymer network clusters at various critical conditions, discuss the structure of critical polymer clusters, and demonstrate some applications.