The fracture of the functionally graded thermal barrier coating (TBC) under the thermal loads is a key for the engineering application of this kind of materials. In the previous studies, the functionally graded TBC is...
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(纸本)0878499709
The fracture of the functionally graded thermal barrier coating (TBC) under the thermal loads is a key for the engineering application of this kind of materials. In the previous studies, the functionally graded TBC is usually simplified into a laminate by homogenizing the material of each interlayer as an isotropic layer. Nevertheless, this method is a macro equivalent method, which neglected the microstructure characteristics of materials. In this paper, the computational micromechanics method (CMM) is employed to study the fracture problem of the functionally graded TBC with the interface crack. Essentially, CMM is a finite element analytical method based on the real microstructure of materials, which combines the digital image processing technique, the auto mesh generation technique with the finite element method. Firstly, the microstructure photos of the functionally graded TBC are required. Secondly, the digital image processing technique and the auto mesh generation technique are used to construct the finite element model. Finally, the finite element method is utilized for the fracture analysis of the functionally graded TBC under the thermal shock loads. Moreover, the problem is also analyzed using the macro equivalent method and the results from the two methods are compared. The temperature field obtained using CMM is basically consistent with the one obtained from the macro equivalent method and the influences of the interface crack on the temperature fields are limited in a local region. But results of the driving forces for the crack propagation, J-integrals, from the two methods are quite different. Comparing with the CMM results, J-integrals from the macro equivalent method are smaller. It means that the macro equivalent method tends to underestimate the driving force of the interface crack. On the other hand, the prediction of the critical location of the interface crack from the two methods is also different. Since the influence of the microstructure
A new approach to produce superfine WC-Co powder by direct reduction and carbonization is proposed. Water-soluble salts containing W and Co were used as raw materials. Tungsten and cobalt oxide powder （CoWO4/WO3） wa...
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A new approach to produce superfine WC-Co powder by direct reduction and carbonization is proposed. Water-soluble salts containing W and Co were used as raw materials. Tungsten and cobalt oxide powder （CoWO4/WO3） was first formed by a spray-pyrolysis technique, which was then mixed with carbon black and converted to WC-Co composite powder at 950℃ for 4 h in N2 atmosphere. The resulting powder has a particle size of 100-300 nm.
The need for WC-Co with improved properties, particularly increased hardness and strength combined with increased ductility and toughness, has focused attention on the development of grades with finer and finer-graine...
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The need for WC-Co with improved properties, particularly increased hardness and strength combined with increased ductility and toughness, has focused attention on the development of grades with finer and finer-grained powders and cemented carbides. The aim of this study is to determine the sintering temperature of nanocomposite WC-6Co (wt.%) sample by using an optical microscope under high temperature and a DSC / TG apparatus. The WC-Co sample was prepared from nanocomposite powder by hot-press-sintering at the determined sintering temperature. The phase structure of the powder and sintered samples was investigated. The SEM imaging was performed on fracture surfaces of sintered samples. The density and the HRA of sintered samples were also measured.
Ti2AlC bulk material with a few amounts of secondary phase Ti3AlC2 was synthesized by in-situ hot pressing TiC/Ti/Al powder mixtures at 1400°C. The synthesis process of Ti2AlC was analyzed based on the XRD patter...
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Ti2AlC bulk material with a few amounts of secondary phase Ti3AlC2 was synthesized by in-situ hot pressing TiC/Ti/Al powder mixtures at 1400°C. The synthesis process of Ti2AlC was analyzed based on the XRD patterns of samples prepared at different temperatures and different soaking time by hot pressing. Results show that Ti reacts with Al to form intermediate phase TiAl at high temperature and then TiAl reacts with TiC forming Ti2AlC. The reaction speed is very fast at the early stage and most Ti2AlC appears during this period. At final stage, TiC and TiAl is very few, reaction speed is slow and secondary phase Ti3AlC2 comes out. Ti2AlC particles synthesized at different temperatures have different microstructure.
Magnetic CoNiWP thin films were prepared by electroless deposition on NiTi shape memory alloy. The effects of electroless deposition time on the micrograph and the magnetic properties of films were investigated by SEM...
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Magnetic CoNiWP thin films were prepared by electroless deposition on NiTi shape memory alloy. The effects of electroless deposition time on the micrograph and the magnetic properties of films were investigated by SEM and VSM respectively. The results showed that the films are amorphous and have good magnetic proper ties. The grains of film were small (1-10 μm) at the beginning, then grew up as big cell (10-40 μm). The coercivity Hc increased then decreased with the increasing of electroless deposition time.
TiO2 thin films were prepared on soda lime glass, fused quartz and stainless steel substrates by liquid phase deposition (LPD) method from a (NH4)2TiF6 aqueous solution upon the addition of boric acid (H3BO3), and the...
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TiO2 thin films were prepared on soda lime glass, fused quartz and stainless steel substrates by liquid phase deposition (LPD) method from a (NH4)2TiF6 aqueous solution upon the addition of boric acid (H3BO3), and then calcined at 500°C for 2 h. The prepared films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It was found that the substrates obviously influenced the element composition and microstructure of TiO2 thin films. Except Ti, O and a small amount of F and N elements, which came from the precursor solution, some Si (or Fe) element in the thin films deposited on soda lime glass and quartz substrates (or on stainless steel substrate) was confirmed. The Si (or Fe) element in the thin films could be attributed to two sources. One was from the SiF 62- ions (or FeF62- ions) formed by a reaction between the treatment solution and soda lime glass or quartz (or stainless steel) substrates. The other was attributed to the diffusion of Si (or Fe) from the surface of substrates into the TiO2 thin films after calcination at 500°C. The Si (or Fe) element in the TiO2 thin films could behave as a dopant and resulted in the formation of composite SiO2/TiO2 (or Fe2O3/TiO2) thin films on the substrates.
Among the preparing methods of ceramic particles reinforced metal matrix composites, the in-situ reaction synthesistechnology has many technical and economical advantages over other traditional methods obviously. Sev...
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Among the preparing methods of ceramic particles reinforced metal matrix composites, the in-situ reaction synthesistechnology has many technical and economical advantages over other traditional methods obviously. Several principal techniques to prepare metal matrix composites by in-situ reactive synthesis method were analyzed in this paper. Based on the analysis, a kind of preparing by using SHS and HP technique which was combustion and in-situ reaction synthesis of dual-phase ceramic reinforced copper-based composites was given. The impact of preparing condition on the structure and the behavior of the material were also researched. At last, some fundamental characteristics of the copper-based composite were studied, compared with the pure copper this kind of copper-based composite kept the electric conductivity and thermal conductivity above 80 percent, at the same time the wear resistance improved 6 times.
In the present paper, magnesium dititanate (MgTi2O5, M2T) was introduced into aluminum titanate (Al2TiO5, AT) to form AT-M2T solid solution so that the thermal shock resistance of Al 2TiO5 could be kept still good whi...
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In the present paper, magnesium dititanate (MgTi2O5, M2T) was introduced into aluminum titanate (Al2TiO5, AT) to form AT-M2T solid solution so that the thermal shock resistance of Al 2TiO5 could be kept still good while without any decomposition. The effect of MgTi2O5 addition on thermal shock resistance of Al2TiO5 was investigated. The experimental results showed that the thermal shock resistance of Al 2TiO5 began to decrease when a little amount of MgTi 2O5 was added and then rose with the continuous addition of MgTi2O5, even overrunning that of pure Al 2TiO5 when 30mol% MgTi2O5 was contained. It was found that fine solid solution was formed between Al 2TiO5 and MgTi2O5, which enhanced the thermal shock resistance of Al2TiO5.
Calcium carbonate particles with different morphologies were fabricated by the precipitation reaction of sodium carbonate with calcium chloride in the absence and presence of the copolymer poly (styrene-alt-maleic aci...
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Calcium carbonate particles with different morphologies were fabricated by the precipitation reaction of sodium carbonate with calcium chloride in the absence and presence of the copolymer poly (styrene-alt-maleic acid) (PSMA) at 80°C, respectively. The as-prepared products were characterized with SEM, XRD, Infrared and BET surface areas. The results showed that the pH of solution and the concentration of PSMA and CaCO3 significantly influenced the morphologies of CaCO3 particles. Various crystal morphologies of calcium carbonate, such as plates, rhombohedras, rods, ellipsoids, dumbbells, peanuts, spheres etc., could be obtained depending on the experimental conditions.
As has been discussed, research on the electronic structure between organic and inorganic atoms in hybrid compounds has become important. In our study, DV—Xα method was employed to calculate the electronic structure...
As has been discussed, research on the electronic structure between organic and inorganic atoms in hybrid compounds has become important. In our study, DV—Xα method was employed to calculate the electronic structure of the hybrid compound. The information obtained from the calculation included orbit charge, bonding order, Fermi energy, density of the state, etc. The influence of organic and inorganic parts on the energy band structure of the hybrid compound was discussed based on the calculation results of Fermi energy and density of state. The chemical bonding between organic and inorganic parts in the hybrid compound was also analyzed in detail according to the orbital charges and bond orders.
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