Papers by Keyword: Microstructure

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Authors: Byeong Ho Kim, Kyung Chul Park, Sung Hak Lee, Yong Ho Park, Ik Min Park
Abstract: The fracture behavior of Mg-5Al-1Zn and Mg-5Al-1Zn-3Sn alloy was investigated by direct observation of microfracture process using an in-situ loading stage installed inside a scanning electron microscope chamber. Crack was initiated at the interface of Mg/second-phase particles or second-phase particles. Fracture of the alloys was predominantly dimple or/and quasi-cleavage failure. The improvement of what could be explained by mechanisms of blocking of crack or shear band propagation, formation of multiple shear bands, crack blunting and shear band branching.
177
Authors: Yu Wang, Hong Li, Ying Guo Yang, Geng Wu Ji, Kong Chao Shen, Hao Liang Sun, Jiong Li, Zheng Jiang, Fei Song
Abstract: The beta-phase of Zn4Sb3 has been regarded as a very promising thermoelectric material since middle nineties, owing to its unique merit: intermediate temperature region (200-400 °C), made of cheap, non-toxic and abundant elements and high thermoelectric property. However, the thermal stability of Zn4Sb3 seems to be an inherent obstacle for the practical application during the working temperatures. Herein, magnesium doped Zn-Sb semiconductor (Mg0.04Zn3.96Sb3) was investigated thoroughly in-situ during thermal annealing up to 600 K, whilst both microstructure and electronic structures were recorded via the combination of synchrotron-based two dimensional X-ray diffraction techniques and the X-ray photoemission spectroscopy. While the time-resolved grazing incidence XRD reveals the preserved crystal structures during thermal annealing to 600 K, XPS measurement demonstrate the robustness of electronic structures. On basis of these findings, it was concluded in the end that the doping of magnesium significantly improves the thermal stability of zinc-antimonite compounds and introduces minor influence on the electronic structure of Zn-Sb alloy. Our study may propose an effective approach towards the wild application of Zn4Sb3 related thermoelectric materials.
178
Authors: Jian De Han, Gang Hua Pan, Wei Sun
Abstract: Environmental Scanning Electron Microscope (ESEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to in situ observation microstructure character changes of hardened cement paste due to carbonation. Three types water-to-cement ratio of 0.53, 0.35 and 0.23 were research. When w/c=0.53, Carbonation enlarged the cracks, and some calcium carbonate spots appear on the calcium hydroxide crystals. When w/c=0.35, less cracks appear, and some white flocculent calcium carbonated appear on the calcium hydroxide crystals than above w/c=0.53 cement paste. When w/c=0.23, the microstructure character before and after carbonation have distinct changes, and some cracks become small or disappeared. Unhydrated cement clinkers continue to hydrate reactions and there are many white SiO2•nH2O (silica gel) after C-S-H gel carbonation in cement paste matrix.
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Authors: Fei Cao, Fen Fen Yang, Xue Jian Wang, Hui Jun Kang, Ya Nan Fu, Tong Min Wang
Abstract: Synchrotron X-ray radiography was used to in situ study the diffusion behavior and microstructural evolution of Al/Cu bimetal. The interface diffusion, dendritic/eutectic growth and the formation of intermetallic compounds around the Al/Cu bimetal interface were analyzed. During the isothermal diffusion process, a liquefied transition zone at the interface with a concentration gradient was formed when the Cu concentration exceeded eutectic composition of Al-Cu alloy. During the solidification of transition zone, the growth sequence of α-Al dendrites and eutectic structure were mainly dominated by the variation of Cu concentration and thermal field according to the temperature of the liquidus line of the equilibrium phase diagram. Finally, the transition zone around the interface were identified to be I (α-Al), II (Al+Al2Cu), III (Al2Cu) and IV (Al2Cu, AlCu and Al4Cu9), respectively.
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Authors: C. M. Hefferan, S. F. Li, J. Lind, Ulrich Lienert, Anthony D. Rollett, R.M. Suter
Abstract: We have used high energy x-ray diffraction microscopy (HEDM) to study annealing behavior in high purity aluminum. In-situ measurements were carried out at Sector 1 of the Advanced Photon Source. The microstructure in a small sub-volume of a 1 mm diameter wire was mapped in the as-received state and after two differential anneals. Forward modeling analysis reveals three dimensional grain structures and internal orientation distributions inside grains. The analysis demonstrates increased ordering with annealing as well as persistent low angle internal boundaries. Grains that grow from disordered regions are resolution limited single crystals. Together with this recovery behavior, we observe subtle motions of some grain boundaries due to annealing.
447
Authors: Jing Wang, Yi Chao Ding, Hong Cheng, Yi San Wang
Abstract: TiC particulates reinforced iron matrix surface composite was produced by cast technique and in-situ synthesis technique. The surface composite was investigated from thermodynamics, microstructure, wear-resistance and oxidation-resistance. The results show TiC particles whose volume fraction is about 40% exhibit fine size in iron matrix on the surface composite. An excellent metallurgy-bond is observed between the surface composite and the gray iron. Fe-TiC surface composite shows good oxidation-resistance at 900°C and great wear-resistance under condition of dry sliding.
80
Authors: Yan Feng Liang, Jing En Zhou, Sheng Quan Dong, Tong Yang
Abstract: Al-4.5 wt. % Cu matrix composites reinforced with in situ SiC particles were synthesized using direct reaction synthesis (DRS). The microstructure and tensile properties of the in situ composites were examined by optical microscopy (OM) and transmission electron microscopy (TEM). The results showed that the in situ SiC particles could be obtained through the appropriate control of the fabrication parameters. The heat released by the formation of TiC effectively promoted the formation of SiC. The size of the in situ SiC particles in the matrix was about 0.2 μm.
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Authors: Lin Zong, Zheng Jun Liu
Abstract: The in-situ ceramic phases reinforced Fe-based surface coating had been produced by prepared high-carbon ferrochromium, ferrovanadium and graphite power on 20g steel through plasma transferred arc weld-surfacing process(PTA). The microstructure and properties were investigated by means of optical microscopy(op), scanning electron microscopy(SEM), X-ray diffraction(XRD) and microhardness meter. The results showed that the substrate and the coating formed good metallurgical bonding.The microstructure of coating consists of primary M7C3 carbide and eutectic structures[M+γ′+M7C3+VC]. The primary hexagonal (Fe,Cr,V)7C3 with larger size evenly distributed in coating and the fine VC particles were globular shape. The microhardness appeared reasonable distribution from substrate to the top ,which ensured that the materials had good abrasive wear resistance.
518
Authors: Fang Zhou, Hui Yao Yang, Liang Hua He
Abstract: A Fe-based composite coating reinforced with in situ synthesized TiC-TiB2 particles was successfully fabricated on Q235A by laser cladding with mixture powder of TiO2, Al, B4C, C and Fe55 as precursors. The microstructure and mechanical properties of coating were investigated. The results show that the main phases of coating are TiB2, TiC, (Fe,Cr)7C3 and α-Fe. TiC particles show the shape of block, TiB2 particles exhibit the shape of strip. Compared with the Q235A, the microhardness of the composite coating improved drastically.
162
Authors: Ping Luo, Shi Jie Dong, Zhi Xiong Xie, Wei Yang, An Zhuo Yangli
Abstract: TiC-TiB2 composite ceramics were successfully fabricated via planetary ball milling of 72 mass% Ti and 28 mass % B4C powders, followed by low temperature sintering process at 1200°C. The microstructure of the ball-milled powder mixtures and composite ceramics were characterized by Differential thermal analysis equipment (DTA), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The results showed that the ball-milled powder mixtures (Ti and B4C powders) were completely transformed to TiC-TiB2 composite ceramics as the powders were milled for 60 h and sintered at 1200°C for 1 h. The formation mechanism of the TiC-TiB2 composite was discussed. The high energy ball milling and necessary sintering for the powder mixtures plays an important role in the formation of the composites.
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