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《应用陶瓷进展》2013,112(6):265-271
AbstractRefractories produced from mixes of Egyptian dolomitic magnesite with talc and low cost Chinese bauxite have been assessed as potential substitutes for the high temperature basic refractory bricks currently used in steelmaking and other industries. Fifteen batches of different compositions were prepared by firing for 2 h up to 1580° C. Six samples were selected for further investigation on the basis of their phase composition and densification parameters. The mineralogical composition and microstructure, pore size distribution, and mechanical and refractory properties of these samples were investigated. All six samples consisted mainly of MgO and MA spinel refractory phases, plus some calcium silicates and aluminoferrite phases. The latter phases contribute to densification during firing by promoting liquid phase formation. Most samples showed high refractoriness under load, good spalling resistance, better mechanical properties than current refractories, and compact microstructure. It is concluded that these new refractories are good candidate materials for the production of shaped linings for industrial kilns and furnaces. 相似文献
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《Science & Technology of Welding & Joining》2013,18(4):357-362
AbstractThe study on the vertical and horizontal spot vibration welding of Inconel 690 alloy was carried out to observe the dendrite morphologies and estimate the temperature gradient G and growth rate R under different vibration conditions. The purpose is to further understand the mechanism of microstructure changes under vibration. Based on different temperature distributions along vertical and horizontal directions in the centre of a melting pool, it is found that vertical and horizontal vibrations induce the divergence of the nucleates site and grain growth rate then affect the grain morphologies. Vertical vibration welding creates a coarse dendrite structure with sturdy secondary and tertiary dendrite arms, and the X-ray diffraction (XRD) profile of this structure shows a strong (200) peak. Horizontal vibration welding results in grain refinement and a relatively disordered structure, which is reflected by its low XRD intensity. The study shows that vibration affects the weld structure by improving nucleates and changing growth rate. 相似文献
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《Journal of Adhesion Science and Technology》2013,27(2-3):175-182
In this paper metallization of a liquid crystal polymer (LCP) substrate by physical vapor deposition (PVD) is described. Pretreatment of LCP substrates with oxygen-containing plasma improves the adhesion strength between the PVD copper layer and substrate. When a nickel interlayer was used, the adhesion was improved further. Still higher adhesion was also achieved with appropriate bias used during deposition of the nickel interlayer by PVD. Even after 1000 cycles of thermal shock the adhesion strength of Cu/Ni on LCP pretreated with oxygen plasma was still high. 相似文献
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《Science & Technology of Welding & Joining》2013,18(1):1-11
AbstractThe present paper evaluates the solderability of three discontinuously reinforced aluminium matrix composites. The tested composites were an aluminium alloy of the 2000 series (AA2014) reinforced with different percentages of silicon carbide particles (6, 13, and 20 vol.-% respectively). A similar study was carried out on the unreinforced aluminium alloy for comparative purposes. Three low temperature filler alloys of the Zn–Al system were used for soldering. Drop formation tests were performed to evaluate the wettability of the molten filler alloys and sample joints (single overlap specimens) were produced to determine solder penetration in the joint clearance. Microstructural studies of the joints were carried out to determine the effects of the solid reinforcement particles on molten pool behaviour and solidification mechanisms. 相似文献
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《应用陶瓷进展》2013,112(5):239-242
AbstractA new method for bonding blocks of Si3N4 has been developed that produces bonds whose maximum service temperature is equal to the temperature used during the bonding process. In the present paper a system consisting of blocks of Si3N4 coated with a preceramic film containing a fine dispersion of silicon and a thin layer of germanium powder has been investigated to determine the effect of the thickness of the germanium film. The maximum service temperature is not determined by the melting point of the germanium since the germanium forms a higher melting point solid solution with the silicon in the film. Control of the thickness of the germanium film is found to be critical as a thicker layers results in lower strength bonds owing to differences in thermal expansion, and the maximum service temperature is lower owing to the lower liquidus temperature of the leaner Ge–Si solid solution. This technique has potential applications in fuel cells as a result of the small differences in thermal expansion coefficients and firing shrinkage in fuel cell materials, thus allowing successful fabrication and joining of monolithic solid oxide fuel cells (MSOFCs) with few defects. 相似文献
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《金属精饰学会汇刊》2013,91(6):303-304
AbstractThe electrochemical reduction of Bi2S3 films deposited using the successive ionic layer adsorption and reaction method in a Bi(III) solution with a sulphidation agent Na2S was investigated in Ni2+ free background and Ni2+ containing electrolytes at different pH. This investigation was carried out by means of cyclic voltammetry, electrochemical quartz crystal microbalance and X-ray photoelectron spectroscopy. It has been established that during the reduction of a bismuth sulphide film in the Ni2+ free background solution the electrode mass decreases due to Bi2S3 film reduction to metallic Bi and the transfer of sulphide ions into the bulk of the solution. At pH=3, the Bi2S3 film reduces under the potential region from –0·2 to –0·4 V, while at pH=4 and 5 from –0·4 to –0·6 V. The processes occurring during the reduction of Bi2S3 film in the Ni2+ containing electrolyte depend on the electroreduction medium. At pH=3, the reduction of Bi2S3 film to metallic Bi and Ni2+ ions occurs simultaneously under the potential region of the cathodic current peak (–0·2 to –0·4 V). When pH is 4 or 5, the increase in electrode mass is caused by the incorporation of Ni2+ ions into the bismuth sulphide film with their partial reduction to the metallic or close to metallic state with the occurrence of structural changes in the film. 相似文献
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《International Journal of Cast Metals Research》2013,26(1-4):54-57
AbstractIn the development of turbine blades, solidification structures have progressed from equiaxed to directionally solidified (DS) and then to single crystal (SX). The transition from DS to SX was achieved by introducing a grain selector which consists of two parts: a starter block referring to the grain orientation optimisation and a spiral part to ensure that only one grain can eventually survive and grow into the blade. With emphasis on the spiral selector, the microstructure evolution and grain competitive growth is visualised using a coupled macroscale ProCAST and mesoscale cellular automaton finite element (CAFE) model in this study. To improve the efficiency of the spiral grain selector and to save cost in casting, the effects of spiral geometries on the grain selection are investigated. Simulation results reveal that the spiral becomes more efficient in grain number selection with a smaller spiral thickness (d T) and a larger spiral diameter (d S). 相似文献
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《Science & Technology of Welding & Joining》2013,18(6):472-482
AbstractIn the present study, the effects of stray grain formation and thermomechanical stresses on solidification cracking in welds of single crystal Ni-base superalloys have been investigated. Welds were made in an asymmetric crystallographic orientation under three different processing conditions. As welding speed and power increased, stray grain formation became extensive, but only on one side of the weld. Solidification cracking also became more extensive and occurred mostly along the stray grain boundaries. The three welding processes have been simulated using the finite element method (FEM). The calculation results showed that thermomechanical stresses increase with welding speed and power, leading to increased susceptibility to cracking. These results agree well with experimental observations. 相似文献
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《International Journal of Cast Metals Research》2013,26(6):422-429
AbstractA new heat conductor (HC) technique was developed to minimise stray grain formation arising from the geometrical effect during single crystal solidification of superalloys. Graphite is recommended as HC material because of its excellent thermophysical properties. Computer simulation and temperature measurements have shown that this technique is able to produce a clear improvement of thermal condition in the critical region of the components. Both the extent and the period of undercooling at the platform extremity significantly decreased. Structural investigation revealed a notable reduction in stray grain quota, providing evidence for the effectiveness of the HC technique for improving the quality of single crystal components. 相似文献