Progresses in Fracture and Strength of Materials and Structures

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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.
679
Authors: Zhong Hua Li, Qing Wang, Dong Li Sun, Li Ping Zhang
Abstract: The effects of hydrogen on the microstructure and hot deformation behavior of Ti-6Al-4V alloy were studied, and the differences of microstructure and high temperature compressive behavior between the specimens hydrogenised various time at 700 oC and with the same hydrogen contents were analyzed. The results showed that the addition of hydrogen decreases the deformation resistance of Ti-6Al-4V alloy at high temperature. The flow stresses of specimens with the same hydrogen content declined as the prolongation of hydrogenating time. The microstructure observation indicated that stick-type microstructure was obtained in Ti-6Al-4V alloy annealed at 700 oC for 2 hours. Hydrogenation at 700 oC for 2 hours resulted in fine α plate in β transformed microstructure. When the hydrogenation time was prolonged to 6 hours, the volume fraction of newly-formed α plates increased and the prior α plates became coarser.
683
Authors: Yan Dong Yu, De Liang Yin, Bao You Zhang
Abstract: Cavity growth is a typical microstructure feature in superplastic forming (SPF) of materials. Substantial growth and interlink of cavities in superplastic deformation usually lead to reduction in elongation, even to failure. Consequently, it is necessary to investigate the mechanism and model of cavity growth. In this paper, experimental studies on cavity growth were carried out by means of superplastic tension of ZK60 magnesium alloys. Scanning electronic microscope (SEM) was employed for observation of fractography. Experimental cavity radius and volume fraction were determined by optical microscopy and corresponding picture-based analysis software. It is found that, the fractured surfaces after a superplastic elongation have a mixed characteristic of intergranular cavities and dimples. Further, the cavity growth is identified to follow a exponentially increasing mode.
687
Authors: Dan Yang Zhu, Liang Zhen, Chen Lin, Wen Zhu Shao
Abstract: This paper presents the high temperature deformation behavior of 7075 aluminum alloy after T6 heat treatment by using electron tensile test machine with a temperature range of 230 - 440 °C, strain rate of 0.01 s-1, deformation of 50 % and 100 %, respectively. The morphology of the fractured surfaces, dislocation and change of sub-grains before and after the tensile test were investigated by using scanning electron microscope (SEM) and electron back scattering diffraction (EBSD) technique. The results show that the fracture mechanism of 7075 aluminum alloy was ductile rupture. The thermal deformation of the 7075 aluminum alloy showed the steady-state flow characteristics, and the flow stress decreased with the increase of deformation temperature. Orientation angle offset of the grain boundary decreased with the increasing of the deformation at 440 °C, indicating that the continuous dynamic recrystallization occurred inside the 7075 aluminum alloy.
691
Authors: Qi Nian Shi, Wei Hao Xiong
Abstract: By the test of Al-Li-Cu-Mg-Zr Alloy’s mechanical property and microstructure in various kinds of extrusion technology, the effect of extrusion processing parameter on the structure and property of the alloy was analyzed, and the parameter’s range for obtaining proper compromise of strength and toughness was discussed.
695
Authors: Qi Nian Shi, Wei Hao Xiong, Sheng Guo Liu
Abstract: The influence of aging process on microstructures and mechanical properties of a rapid solidification Aluminum-Lithium alloy has been analyzed in this paper. The results show that the better aging process is as follows: heating to 170oC for 4 hours and then followed by a final aging at about 190 oC for 18 hours. A lot of fine participated second phase such as δ′ in matrix and a narrow participation free band make alloy’s good performance.
699
Authors: Zhan Cheng, Andrew Godfrey, Yu Bin Zhang, Wei Liu, Qing Liu
Abstract: Polycrystalline nickel (99.999% purity) cold-rolled to a reduction of 96% has been given a two-step annealing treatment consisting of a pre-annealing at 180 °C or 220 °C for 2 hours, followed by a final annealing at 300 °C for 10 minutes. The changes in microstructure and texture during annealing have been followed using electron backscatter diffraction orientation measurements taken on the longitudinal section of the samples. The results suggest that pre-annealing at low temperature can enhance the formation recrystallized grains of cube orientation. Based on an analysis of the experimental data, possible reasons for the enhancement as a result of pre-annealing in the formation of cube orientation grains are discussed.
703
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
707
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.
711
Authors: Jian Peng, Rong Shen Liu, Ding Fei Zhang, Cheng Meng Song
Abstract: The microstructures and mechanical properties of Mg-Zn-Zr-Y alloy extruded bar with different heat treatment processes were investigated, including solution treatments of 400 oC, 450 oC and 500 oC for 3 hours followed by 170 oC×24h aging treatment, and solely aging treatments of 160 oC, 180 oC for 24hours without solution after extruding. By comparing the grain size, strength and elongation of the samples, the heat treatment processes for extruded products with high strength and with medium strength were recommended.
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