Advanced Materials Research Vols. 287-290

Abstract: The preparation and superconductivity of Tl-2212 films grown on CeO₂-buffered MgO substrates were investigated. AFM showed that the annealing of MgO substrates remarkably improved their crystal quality of surface layers, and led to the surface morphology of substrates evolving into unattached outgrowth structure with ultra-smooth surface. XRD measurements showed that CeO₂ buffer layers grown on MgO annealed at the suitable conditions were pure (00l) phase. The 500 nm thick Tl-2212 films grown on these CeO₂ films subsequently possessed excellent c-axis orientation and superconductivity. The best Tl-2212 film reached a low surface resistance of about 324 μΩ (10 GHz, 77 K), a critical current density as high as 3.5 MA/cm² (77 K, 0 T) and a critical transition temperature of about 108.4 K.

Abstract: The effect of the quenched speed on the microstructure and electromagnetic properties of melt spun Nd3Fe₆₈Co₁₈B₁₁ nanocomposites was investigated. XRD spectra showed that only α-Fe phase can be obtained for both quenched samples. The complex permeability () and permittivity () within 2-18GHz were measured by vector network analysis. By virtue of quenched speed increased, the flake-like Nd₃Fe₆₈Co₁₈B₁₁ decreased the value of permittivity while that of permeability slightly changed. According to transmission line theory, the reflection loss was calculated. With thin matching thickness of 1.5mm, The Nd₃Fe₆₈Co₁₈B₁₁ composites realized the optimum reflection loss RL=-5.3dB at 3.6GHz and RL=-3.5dB at 3.9GHz for quenched speed 30m/s and 20m/s, respectively. It showed that it is possible to obtain good microwave absorbing properties with appreciated quenched speed for as spun Nd-Fe-B nanocomposites.

Abstract: Carbon fiber powder (CFP) instead of the traditional glass fiber (cloth) was used to reinforce epoxy resin for rapid tooling. There are two obvious advantages: one is to utilize the waste materials, which is good for the protection of the environment; another is to simplify the producing process by cast molding. The filling amount and dispersing process of CFP was studied in this paper. The results show that when the amount of CFP was 10 wt%, and the ultrasonic time is more than 15 min, the CFP can be dispersed in the epoxy matrix uniformly, and the mechanical properties can meet the requirement of epoxy molding.

Abstract: Cordierite material was prepared by talc, bauxite and kaolin, and the coefficient of thermal expansion (CTE) of cordierite crystals could be determined by high temperature X-ray diffractmeter: the volume and average liner CTE is 2.31×10^-5°C-1 and 0.84×10^-5°C-1 (200°C -800°C) respectively; With the temperature increasing, the CTE in a or b axis direction increases, and in c axis direction decreases rapidly below 400°C then slowly, cordierite crystal is of obvious thermal expansion anisotropy. The orientation of crystal in sample is random, expansion and shrinkage partly counteract, so that the CTE of cordierite materials is low.

Abstract: Using Al, MgO and Al₂O₃ as raw materials, Al₂O₃-MgAlON composite was synthesized in N₂ atmosphere by hot-press sintering at 900°C. Cracks prepared on the sample surface were healed at 1200°C×6hrs. Phase composition and element chemical state of sample were studied before and after healing. The results showed that: after healing process Al and MgO phase disappeare, and AlN and MgAlON phase appear, all kinds of elements in Al₂O₃-MgAlON material change their chemical state after the healing treatment, the changed electronic binding energy is Al 0.05ev, Mg 0.08ev, O 2.58ev or N 1.02ev respectively, and the chemical composition and crystal structure of MgAlON phase also change, all these change are helpful for crack healing process of Al₂O₃-MgAlON material.

Abstract: T-tube is widely used in aeronautics and astronautics, pipeline, petrochemical, light industry, automobile, life supplies and so on. The forming process of T-tube is non-symmetric deformed and the material deformation laws are very complicated, so it is quite difficult to machine a produce. In this paper, based on the software ABAQUS, the numerical simulation model was set up and then the high-pressure and axial feeding bulging process of T-tube was simulated. It was analyzed that the main process parameters, such as internal pressure, axial feeding and central punch displacement, had influenced the tube forming quality. The research results show that: (1) The wall thickness of branch becomes thinner and the height of branch does not increase higher in the forming process. (2) With the increment of axial feeding displacement, the wall thickness of tube becomes thicker and the height of branch becomes higher quickly. (3) At the pressure of 110MPa, the wall thickness at the top of branch becomes thinner gradually with the increasing distance between initial position of central punch and tube. (4)When the friction coefficient of surfaces was 0.06 and the ideal branch was produced, the proper parameters of axial feeding bulging processes are as follow: the internal pressure is from 110MP to 120MP, the axial feeding displacement is 14～16mm and the distance between central punch and main tube is from 0mm to 4mm.

Abstract: Long afterglow luminescent materials Sr_2-xCa_xMgSi₂O₇:Eu²⁺,Dy³⁺ （x=0-1.955）was synthesized by combustion method and characterized by X－ray diffraction,fluorescencespectrum and so on. Its preparing process conditions,the effect of Ca²⁺ replacing Sr²⁺ on its Luminescent performance were discussed. The results show it has a single phase and foamy structure,which is easy to be grinded into superfine powders. Its Luminescent property is importantly affected by water dosage(R= n_H2O /n_TEOS), reducer dosage (H=n_reducer /n_nitrate), gel grain dosage , gel grain size, arousing-burning temperature and burning time. Its best preparing process conditions are determined. A small quantity of Ca²⁺ replacing Sr²⁺ can raise its luminescence performance. Increasing Ca²⁺ content, its emission peak gradually wave to the long wave traverse, its luminous colors change from blue to yellow. Compared with the sample synthesized by high temperature solid reaction,the emission peaks of the sample synthesized by combustion method distinctly take place red shift.

Abstract: Based on the elastic theory of anisotropic materials multilayers, using the finite element method, the dynamic characteristics are investigated for the composite structure which is composed of the electromagnetic multiferroic layer and isotropic metal layer. Firstly, the finite element model of the multilayers structure is built with shell and solid elements capable of contributing anisotropic materials. Then, based on the model analyses, the natural characteristics of the composite structure are obtained with considering the electric-magnetic-elastic effect and the layer thickness. It is also shown that the electromagnetic effects have a certain influence on the natural frequencies vibration patterns, and the thickness of the multiferroic layers has more important influence.

Abstract: The cause of cracks after brush-plating on the main speed reducer of helicopter was analyzed and the ameliorative measures by shot-peening were brought forward consolidation. The measure, the components of plating liquid and the master parameters of working procedures were itemized, which can apply to renovation of accessory’s abrasion and scars in the situation of big alternant load.

Abstract: Effects of TiO₂ on crystalline phase of mold fluxes were studied by the mineral phase microscope and the XRD. The results showed that on the experimental condition, the main crystalline phase of mold fluxes were cuspidine, wollastonite and melilite. When TiO₂ added into the mold fluxes, perovskite would be found. TiO₂ promoted Perovskite to crystallization and limited Cuspidine to growth. The morphologies and content of wollastonite and melilite were greatly affected by TiO₂ adding, especially, as 20% TiO₂ added into the mold fluxes.