Papers by Author: Qing Liu

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Authors: Xin Lu Li, Wei Liu, Andrew Godfrey, Qing Liu
Abstract: A 10 Tesla magnetic field was applied during annealing of cold-rolled high purity Ni at 300°C for 2 hours, with samples aligned at various different angles to the magnetic field direction. The effect of the magnetic field annealing on the cube texture evolution and the microstructural development was investigated by use of electron backscatter pattern (EBSP) analysis in the scanning electron microscope. The results show that both the cube texture evolution and the grain size are affected by the application during annealing of a high strength magnetic field, and that the effect varies as a function of the angle between the sample normal and the magnetic field direction. The cube texture volume fraction resulting from 2 hours annealing increases with increasing angle between the field direction and the sample normal direction, though in nearly all cases lower cube volume fractions were obtained compared to annealing without a magnetic field. The average size for all grains and for just cube-oriented grains both decrease with decreasing cube texture fraction, suggesting that the presence of a magnetic field either leads to enhanced recrystallization nucleation, or to a retardation of grain growth after recrystallization.
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Authors: Kun Li, Andrew Godfrey, Wei Liu, Qing Liu
Abstract: A pure Ni single crystal of Cube orientation (001)/[100] have been deformed by reversible cold rolling to a reduction of 98% following an initial extrusion treatment. The microstructure in the as-deformed samples and in partly recrystallized specimens have been characterized in the scanning electron microscope using electron backscattered diffraction (EBSD). Line scans along the normal direction across the sample thickness show some evidence for a macroscopic pattern of subdivision. The EBSD measurements show that the deformed sample is characterized by large jumps in orientation between alternating S and Br orientations, related by misorientation angles of 50°~60°. In part of the sample a background cumulative change in orientation is seen, though local large change in orientation are also still seen. In annealed samples it is found that the orientations of the new grains
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Authors: Jia Jiang, Andrew Godfrey, Qing Liu
Abstract: In order to improve the formability of magnesium alloys at low temperatures, a thorough understanding of the twinning behaviour is required. Cylindrical samples were compressed uniaxially from room temperature to 250oC, with the compression axis parallel to the transverse direction (TD) of a hot-rolled Mg-3Al-1Zn sheet. Twinning was investigated by use of orientation maps constructed from electron backscattered diffraction (EBSD) data. Tensile twinning was observed at all temperatures. In some grains two twin variants were observed. For each twin the specific twinning variant among the 6 possible twinning systems was identified by consideration of the twinning rotation. The twinning was then investigated by comparing the specific twin variant with the calculated Schmid factors for all 6 possible twin variants. In cases of grains that are completely reoriented by two twin variants it is possible to back-calculate the initial grain orientation by considering all possible twin rotations for both of the twin variants. It was found that the operative twin variants where those with the highest Schmid factors.
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Authors: Xiao Ling Li, Wei Liu, Andrew Godfrey, Qing Liu
Abstract: The influence of an electric field on the annealing of high purity (99.999%) cold rolled nickel has been investigated. Annealing was carried out for 2 hours at temperatures between 300oC and 800oC with and without an electric field of strength 2.0KVcm-1. The microstructure and fraction of cube texture resulting were characterized using electron backscattering pattern (EBSP) technique. Annealing in an electric field leads to somewhat smaller average values of the cube fraction and grain sizes compared to annealing without an electric field. The highest temperature (800oC) annealing in an electric field results in microstructures with a lower fractional twin boundary length.
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Authors: H.S. Chen, Andrew Godfrey, Qing Liu
Abstract: The effect of orientation noise in EBSP data on measurement of percolation threshold values has been investigated by use of computer simulated microstructures. A 2-D Monte Carlo Potts model run on a square lattice of size 200 x 200 was used to generate a microstructure containing approximately 150 grains. Orientations were then assigned to each of these grains to generate single texture component microstructures of differing texture tightness (“model” data). In order to simulate the effect of orientation noise on the experimental data, the orientation at each point in the 200 x 200 grid was adjusted in a manner consistent with experimental observations of the effect of orientation noise. The model data represent therefore an underlying real grain structure, and the noise-adjusted data represent the orientation map that would be measured using EBSP analysis at a given orientation noise level. The misorientation angle q70% at which 70% of the grains were percolatively connected was then determined for both the ideal data and for the orientation noise adjusted data. A comparison of the two allows calibration of the extent to which percolation data may be incorrectly estimated by EBSP measurements.
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Authors: J. Jiang, Andrew Godfrey, Qing Liu
Abstract: The hexagonal crystal structure of AZ31 results in a very high mechanical anisotropy and a poor formability of this alloy. In order to address these problems the influence of twinning, slip and dynamic recrystallization (DRX) on the microstructure and texture evolution during compression of AZ31 has been studied over a range of temperatures. Cylindrical samples were tested uniaxially in compression from room temperature to 350oC, with the compression axis parallel to either the normal direction (ND) or the transverse direction (TD) of the hot-rolled sheet from which the samples were cut. The microstructure was characterized using electron backscattered diffraction (EBSD) analysis. Extensive twinning was only observed in the TD samples at all temperatures. The effect of the difference in twinning and slip between the TD and ND samples on the mechanism of dynamic recrystallization has also been investigated. For this, the grains formed during DRX were identified by their appearance in EBSD orientation maps and the orientations of these grains determined.
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Authors: Fu Sheng Pan, Jian Peng, Ai Tao Tang, Jing Zhang, Qing Liu, Z. Xiao Guo
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Authors: Yu Bin Zhang, Andrew Godfrey, Mark A. Miodownik, Wei Liu, Qing Liu
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Authors: Feng Xiang Lin, Andrew Godfrey, Qing Liu
Abstract: The dependence on the grain orientation of the alignment of planar dislocation boundaries in plastically deformed metals has been investigated by examining grains of S orientation ({123}<63-4>) in cold-rolled polycrystalline aluminum. For the ideal S orientation the {111} slip plane associated with the highest resolved shear stress lies either at +40° or -40° to the rolling direction in the longitudinal section, with two S variants corresponding to each case. Boundary traces in S orientation grains in the rolled sample were examined by the combined use of electron channeling contrast imaging and electron backscatter diffraction orientation mapping. In each case the +/- sense of the observed planar boundary traces matched that of the {111} slip plane with the highest resolved shear stress showing that the alignment of the boundaries is predominantly controlled by crystallographic rather than macroscopic considerations.
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