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961.
N. C. Sheng J. D. Liu T. Jin X. F. Sun Z. Q. Hu 《Metallurgical and Materials Transactions A》2013,44(4):1793-1804
The microstructural evolution and bonding behavior of transient liquid phase (TLP) bonded joints for single-crystal superalloy samples with a 300-μm-wide gap have been investigated. The results show that at the initial stage, the interface grows with a cellular structure. With the increase of time, the length and numbers of the cellular structures decrease. At the final stage, the interface evolves with a planar manner. The gradient of B ahead of the liquid/solid interface exists and becomes sharper from the initial to the final analyzed from the electron probe microanalysis (EPMA) results. Inevitably, isolated grain forms during the evolution of the interface and the growth rate of isothermal solidification zone (ISZ) changes through the whole bonding process, and these both deviate from the traditional TLP bonding models. The mechanisms of the formation of the isolated grain boundaries and the reasons for the deviation of the solidification rate are discussed. Also, some effective methods to avoid the formation of isolated grain boundaries in the ISZ are proposed. 相似文献
962.
A kaolin containing 31 wt.% halloysite and a relatively pure kaolin were selected to study the effects of halloysite on the dissolution behavior of precursors and the formation of geopolymers. The Al and Si concentrations in the leached solutions were studied by inductively coupled plasma-optical emission spectrometry (ICP-OES). The reaction process of metakaolin–activator mixtures was monitored by isothermal conduction calorimetry (ICC) while the reaction products were examined by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and mercury intrusion porosity (MIP). Results showed that the halloysite containing kaolin and its metakaolin possessed higher Si and Al dissolution rate than the purer kaolin and its metakaolin. When mixed with sodium silicate activator at 20 °C, the presence of halloysite in kaolin led to a higher geopolymerization rate of metakaolin as reflected by the heat evolution rate. The presence of halloysite improved the reactivity of metakaolin but did not change the geopolymerization pathway under 20 °C air curing and 80 °C steam curing conditions. The products from the two metakaolins had a similar XRD characteristic (i.e. a typically amorphous diffraction). Only a minor difference in the pore distribution and the porosity was found between those products from the two sources of metakaolins. 相似文献
963.
964.
J. X. Hou C. W. Zhan X. L. Tian X. C. Chen Yong-Suk Kim Heeman Choe 《Metallurgical and Materials Transactions A》2012,43(11):4023-4027
The temperature-dependent viscosity and X-ray diffraction (XRD) patterns of a Cu65Sn35 melt were investigated at high temperatures. The viscosity of the melt changed discontinuously at about 1283?K (1010?°C). An XRD analysis of the Cu65Sn35 melt revealed no obvious changes in the correlation radius, whereas the coordination number increased abruptly at a similar temperature with that mentioned previously, i.e., 1283?K (1010?°C) during the cooling process. The results indicate a redistribution of atoms in the nearest environment. The structural transition at the higher temperature was attributed to a change of combination mode of nearest atoms in the short-range order cluster of the Cu65Sn35 melt. 相似文献
965.
The microstructures of the in-situ Mg-based bulk-metallic-glass (BMG) matrix composites synthesized by the copper-mold casting are inhomogeneous, and the optimized mechanical properties are usually realized through alloy composition design. In this article, Mg-based BMG matrix composites containing uniform flake-shaped precipitates with a fixed composition of Mg70Cu8.33Ni8.33Gd8.33Zn5 were synthesized by the Bridgman solidification. Adjusting the withdrawal velocities controlled the size and volume fractions of the precipitates in the composites, and large plasticity was obtained by controlling the cooling condition only. Thus, the Bridgman solidification is an effective way not only to fabricate the homogeneous BMG matrix composites but also to tailor and optimize their mechanical properties. 相似文献
966.
M. Morales M.E. Navarro X.G. Capdevila J.J. Roa M. Segarra 《Ceramics International》2012,38(5):3713-3722
A simple gel-casting method was successfully combined with the spray-coating technique to manufacture graded anode-supported micro-tubular solid oxide fuel cells (MT-SOFCs) based on samaria-doped ceria (SDC) as an electrolyte. Micro-tubular anodes were shaped by a gel-casting method based on a new and simple forming technique that operates as a syringe. The aqueous slurry formulation of the NiO–SDC substrate using agarose as a gelling agent, and the effect of spray-coating parameters used to deposit the anode functional layers (AFLs) and electrolyte were investigated. Furthermore, pre-sintering temperature of anode substrates was systematically studied to avoid the anode–electrolyte delamination and obtain a dense electrolyte without cracks, after co-sintering process at 1450 °C. Despite the high shrinkage of substrate (~70%), an anode porosity of ~37% was achieved. MT-SOFCs with ~2.5 mm of outer diameter, 370 μm thick substrate, 20 μm thick AFLs and 15 μm thick electrolyte were successfully obtained. The use of AFLs with 30:70 and 50:50 wt% NiO–SDC allowed to obtain a continuous gradation of composition and porosity in the anode–electrolyte interface. 相似文献
967.
Y.T. Pei D. Martinez-Martinez J.P. van der Pal X.L. Bui X.B. Zhou J.Th.M. De Hosson 《Acta Materialia》2012,60(20):7216-7225
This paper focuses on the frictional behavior of flexible diamond-like carbon (DLC) film-coated hydrogenated nitrile butadiene rubber. By making use of the substantial thermal mismatch between DLC film and rubber substrate, a dense network of cracks forms in the DLC films and contributes to flexibility. The influence of the size of DLC film microsegments on the frictional performance is studied. The effect of viscoelasticity of the rubber substrate on the frictional behavior of the DLC film-coated system is scrutinized by tribo-tests and theoretical analysis. The importance of adhesive and hysteresis contributions to friction is revealed, and an overarching model is presented. 相似文献
968.
A numerical method for fragmentation is presented that combines the finite element method with the impulse-based discrete element method (impulse-based FDEM). In contrast to existing methods, fragments are not represented as a conglomeration of spheres; instead, their shapes are represented using solid modeling techniques, and are the result of multiple fracture growth. Fracture growth within each three-dimensional fragment is controlled by stress intensity factors computed using the finite element method and the reduced virtual integration technique. Non-convex fragment interaction and movement is modeled using impulse dynamics, rather than a penalty-based method. Collisions leading to fracture are handled individually by propagating pre-existing internal flaws and cracks. The method utilizes decoupled geometry and mesh representation, and local failure and propagation criteria. Fractures that reach volume boundaries lead to further fragmentation. The approach is demonstrated by the fragmentation of a sphere, which exhibits a velocity-dependent fragment size distribution. The distribution is characterized by a two-parameter Weibull distribution, an emergent property of the simulation. Results are in good agreement with experimental data. 相似文献
969.
This paper proposes an integrated method for preventive maintenance and inventory control of a production line, composed of n machines (n?≥?1) without intermediate buffers. The machines are subject to failures and an age-dependent preventive maintenance policy is used. Approximate analytical results are proposed for the one machine case. Simulation software is used to model and simulate the behaviour of the production line of n machines under various maintenance and inventory control strategies. A methodology combining the simulation and genetic algorithms is proposed jointly to optimize maintenance and inventory control policies. Results are compared with the analytical solutions. 相似文献
970.
Metallic glass-based chiral nanolattice: Light weight,auxeticity, and superior mechanical properties
Metallic glasses (MGs) possess large elastic limit and high strength, but unfortunately they are of limited commercial utility due to their macroscopic brittle nature. Here, we report that a chiral nanolattice can be used to design large-scale MGs with negative Poisson’s ratio, large elastic deformation capability, extensive hardening, and large ductility. Furthermore, the mechanical behaviors of the metallic glass chiral nanolattice (MGCN) can be significantly altered through changing the thickness and length of the ligaments in the nanolattice. An exceptional combination of high strength and ductility is observed for MGCN with thin and long ligaments, wherein the sample density is only twice that of water. The deformation mechanism that characterizes the chiral topology is a combination of rotation of the nodes with bending and extension of the ligaments, leading to the extraordinary mechanical behaviors. The present study not only offers a potential solution to mitigating the brittleness of MGs, but also provides some guidelines in designing large-scale MG meta-materials for prospective applications in the fields of acoustics and energy absorption. 相似文献