Papers by Author: Lin Geng

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Authors: Lin Geng, Bin Xu, Y.T. Li, Ai Bin Li, Gui Song Wang
Abstract: (α+β)/β phase transformation temperature of a TC11 titanium alloy was confirmed to be 1035°C, which was obtained by three methods including the calculation method, differential scanning calorimetry and metallographic techniques. Based on this result, annealing treatments below and above the (α+β)/β phase transformation temperature were carried out, and the microstructure of the TC11 alloys before and after annealing treatment was analyzed by SEM. The result showed that conventional annealing below 1035°C does not change the Widmanstaten structure of TC11 alloy, though the thickness of α lamellar structure becomes thicker with increasing the annealing temperature. The microstructure of the TC11 alloy treated by annealing above the α+β/β transformation temperature is non-uniform because of the different forming temperature and growing duration of α phase in the TC11 alloy.
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Authors: Hong Yu Xu, Lin Geng, Qing Chang Meng
Abstract: In this paper, pure aluminum and Al-Cu (1%, 3% and 5% mass.) alloy matrix composites reinforced with 40Vol% Al2O3-SiO2 sort fiber were fabricated by Squeeze-casting technique. Microstructure and tensile properties of the composites were investigated by means of SEM, EPMA, TEM and tensile tests. It was found from the experimental results that when pure aluminum, which was added into Cu elements, is used as matrix, chemical reaction occurred at the interface between amorphous SiO2 and matrix due to the Cu element diffusion and enrichment towards the sort fiber surface. Results indicated that with the increasing of Cu content the ultimate tensile strength decreased firstly then increased continuously.
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Authors: Guo Jian Cao, Lin Geng, Yong Liang Guo, Masaaki Naka
Abstract: In this work, Ni-Al-Ti-B composite powders with Ni: Al: Ti: B atom ratio of 5.7: 1.9:1:1 were prepared by using mechanical activation (MA) method. The MA processes were performed by vibration ball mill in a water-cooled chamber for 30 h. The ball-to-powder weight ratio was 10:1. In order to reduce the oxidation of the powders during milling process, ball milling was performed under an Argon atmosphere. The evolution of morphology and microstructure of Ni-Al-Ti-B composite powders were examined at different milling stages using scanning electron microscope and X-ray diffraction. Distribution of powders size was analyzed and the results showed that there were three stages for the change of powders size: (1) at the first stage, powders size increased due to more welding than fracture of the powders within 2h of MA, (2) at the second stage, particle size continuously decreased until 16h of MA due to more fracturing than welding, and (3) after 16h of MA, the particle size remained constant when welding and fracture reached an equilibrium. Calculation results according to Scherrer equation from X-ray pattern showed that the effective grain size continuously decreased with MA time. X-ray diffraction pattern confirmed that the formation of Ni and Ti solid solution during MA process of the Ni-Al-Ti-B composite powders.
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Authors: Q.W. Wang, Y.C. Feng, Guo Hua Fan, Gui Song Wang, Lin Geng
Abstract: In this paper, the milling process of WO3 and aluminum particles is studied. Influences of rotate rate, milling time and ball-to-powder weight ratio on the morphology and grain size of the particles are studied by scanning electronic microscope and X-ray diffraction techniques. Al particle size decreases firstly and then increases with increasing milling time, while Al grain size decreases gradually as the milling time increases. WO3 particle is distributed uniformly in Al particles after milling for 9h, and has no marked change as further extension of milling time. With increasing the ball-to-powder weight ratio and rotate rate, both particle size and grain size of Al decreases. milling parameters have almost no effect on the grain size of the WO3 particles.
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Authors: Ai Bin Li, Qing Yuan Meng, Lin Geng, Guo Jian Cao, Wen Bin You, Yi Wu Yan
Abstract: The effect of temperature on strain softening behavior of composites with small misaligned whiskers is investigated. The results show that the temperature affects the matrix and whisker mechanical behavior and corresponding composite deformation behavior. With increasing temperature, the whisker rotation angle increases, but their breakage decreases. Meanwhile elevating temperature not only reduces the matrix flow stress and work hardening rate, but also decreases load transfer from the matrix to the whiskers and stress induced by the whisker rotation and breakage.It is found that during hot compression, strain softening behavior of composites decreases as temperature increases.
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Authors: Lin Geng, Yi Wu Yan
Abstract: The coefficients of thermal expansion (CTEs) of the 20 vol% SiCp/Al composites fabricated by powder metallurgy process were measured and examined from room temperature to 450°C The SiC particles are in three nominal sizes 5μm, 20μm and 56μm. The CTEs of the SiCp/Al composites were shown to be apparently dependent on the particle size. That the larger particle size, the higher CTEs of the composites, is thought to be due to the difference in original thermal residual stresses and matrix plasticity during thermal loading. The thermal conductivity of the composites also increases with particle size increasing.
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Authors: Guo Hua Fan, Lin Geng, Zhen Zhu Zheng, Guo Jian Cao, Yu Jie Feng, Yan Kun Liu
Abstract: In this paper, a BaPb0.6Ce0.4O3 (BPCO)/Al matrix composite with a good anti-radiation property was fabricated by hot pressing in air for the first time. Differential scanning calorimeter (DSC) and Thermal Gravimetric (TG) analysis of the compacted blended powders were performed in air to study the oxidation behavior, by which the hot-pressing parameters were determined. Transmission electron microscope (TEM) images and X-ray diffraction pattern showed that there was an incomplete reaction between aluminum alloy matrix and BPCO particles during fabrication process. Compared with the aluminum alloy matrix, the X-ray and γ-ray absorption abilities of the composite were increased by 68.05% and 46.63%, respectively.
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Authors: Yi Wu Yan, Lin Geng, Ai Bin Li, Guo Hua Fan
Abstract: By incorporating the Taylor-based nonlocal theory of plasticity, the finite element method (FEM) is applied to investigate the effect of particle size on the deformation behavior of the metal matrix composites. In the simulation, the two-dimensional plane strain and random distribution multi-particles model are used. It is shown that, at a fixed particle volume fraction, there is a close relationship between the particle size and the deformation behavior of the composites. The yield strength and plastic work hardening rate of the composites increase with decreasing particle size. The predicted stress-strain behaviors of the composites are qualitative agreement with the experimental results.
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