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991.
R.K. Rhein M.D. NovakC.G. Levi T.M. Pollock 《Materials Science and Engineering: A》2011,528(12):3973-3980
The fabrication and high temperature performance of low thermal expansion bimetallic lattices composed of Co-base and Nb-base alloys have been investigated. A 2D sheet lattice with a coefficient of thermal expansion (CTE) lower than the constituent materials of construction was designed for thermal cycling to 1000 °C with the use of elastic-plastic finite element analyses. The low CTE lattice consisted of a continuous network of the Nb-base alloy C-103 with inserts of high CTE Co-base alloy Haynes 188. A new coating approach wherein submicron alumina particles were incorporated into (Nb, Cr, Fe) silicide coatings was employed for oxidation protection of the Nb-base alloy. Thermal gravimetric analysis results indicate that the addition of submicron alumina particles reduced the oxidative mass gain by a factor of four during thermal cycling, increasing lifetime. Bimetallic cells with net expansion of 6 × 10−6/°C and 1 × 10−6/°C at 1000 °C were demonstrated and their measured thermal expansion characteristics were consistent with analytical models and finite element analysis predictions. 相似文献
992.
S.G. HuangK. Vanmeensel O.J.A. MalekO. Van der Biest J. Vleugels 《Materials Science and Engineering: A》2011,528(3):1302-1309
Monolithic B4C, TiB2 and B4C-TiB2 particulate composites were consolidated without sintering additives by means of pulsed electric current sintering in vacuum. Sintering studies on B4C-TiB2 composites were carried out to reveal the influence of the pressure loading cycle during pulsed electrical current sintering (PECS) on the removal of oxide impurities, i.e. boron oxide and titanium oxide, hereby influencing the densification behavior as well as microstructure evolvement. The critical temperature to evaporate the boron oxide impurities was determined to be 2000 °C. Fully dense B4C-TiB2 composites were achieved by PECS for 4 min at 2000 °C when applying the maximum external pressure of 60 MPa after volatilization of the oxide impurities, whereas a relative density of 95-97% was obtained when applying the external pressure below 2000 °C. Microstructural analysis showed that B4C and TiB2 grain growth was substantially suppressed due to the pinning effect of the secondary phase and the rapid sintering cycle, resulting in micrometer sized and homogeneous microstructures. Excellent properties were obtained for the 60 vol% TiB2 composite, combining a Vickers hardness of 29 GPa, a fracture toughness of 4.5 MPa m1/2 and a flexural strength of 867 MPa, as well as electrical conductivity of 3.39E+6 S/m. 相似文献
993.
Zhitong Chen Guang Li Zhenqiang Wu Yuan Xia 《Materials Science and Engineering: A》2011,528(3):1409-1414
This paper investigates the in situ tensile cracks propagating behavior of composite coatings on the aluminized steel generated using the plasma electrolytic oxidation (PEO) technique. Cross-sectional micrographs and elemental compositions were investigated by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The composite coatings were shown to consist of Fe-Al, Al and Al2O3 layers. The cracks propagating behavior was observed in real-time in situ SEM tensile test. In tensile process, the cracks were temporarily stopped when cracks propagated from Fe-Al layer to Al layer. The critical crack opening displacement δc was introduced to quantitatively describe the resistance of the Al layer. There was a functional relation among the thickness ratio tAl/tAl2O3, the δc of composite coatings and tensile cracks’ spacing. The δc increased with the increasing of the thickness ratio (tAl/tAl2O3). The high δc value means high fracture resistance. Therefore, a control of the thickness ratio tAl/tAl2O3 was concerned as a key to improve the toughness and strength of the aluminized steel. 相似文献
994.
The purpose of this study was to evaluate the influence of a composite interlayer (at the metal-ceramic interface) on the shear bond strength of a metal-ceramic composite when compared with a conventional porcelain fused to metal (PFM).Several metal-ceramic composites specimens were produced by hot pressing. To identify which was the best composition for the interlayer several composites, with different relations of metal/ceramic volume fraction, were bonded to metal and to ceramic substrates. The bond strength of the composites to substrates was assessed by the means of a shear test performed in a universal test machine (crosshead speed: 0.5 mm/min) until fracture. Some interfaces of fractured specimens as well as undestroyed interface specimens were examined with optical microscope and scanning electron microscope (SEM/EDS).The shear bond strength results for all composites bonded to metal and to ceramic substrates were significantly higher (>150 MPa) than those registered in the upper range of conventional porcelain fused to metal (PFM) techniques (∼80 MPa). The use of a composite interlayer proved to enhance metal/ceramic adhesion in 160%. 相似文献
995.
Zhigang Jia Kuankuan PengYanhua Li Rongsun Zhu 《Materials Science and Engineering: B》2011,176(11):861-865
Magnetic γ-Fe2O3/activated carbon microspheres have been synthesized by an activation process of carbon microspheres containing iron oxides, which were prepared by hydrothermal method. The structure and morphology of the magnetic porous carbon microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), thermogravimetry and differential thermal analysis (TG-DTA) and N2 adsorption-desorption technique. The results showed that the as-prepared activated carbon spheres were the composite of single-phase γ-Fe2O3 and activated carbon material, and the content of carbon was about 3.87%. Using methyl orange as model pollutant, the magnetic porous carbon microspheres showed good adsorption capacities of 44.65 mg/g. The isotherm evaluations revealed that the Langmuir model attained better fits to the experimental equilibrium data than the Freundlich model. These magnetic porous carbon microspheres could potentially be applied in separation processes. 相似文献
996.
997.
998.
采用高能球磨法和溶胶-凝胶方法制备了碳纳米管掺杂的Ti02纳米复合粉体,通过扫描电子显微镜、X射线衍射、紫外分光光度计等方法对比分析了复合粉体的形貌、微观结构以及光催化活性.实验结果表明,5%碳纳米管掺杂的Ti02复合粉体的光催化活性得到了有效提高,其中高能球磨法制备的复合粉体颗粒细小、分布均匀,具有更好的光催化活性和... 相似文献
999.
Hongyan Zhu ) Baochang Wu ) Dihong Li ) Dongxing Zhang ) Yuyong Chen ) ) School of Materials Science Engineering Harbin Institute of Technology Harbin China ) Harbin Aircraft Industry Co. Ltd. Harbin China 《材料科学技术学报》2011,27(1):69-73
This paper aims at investigating the effect of voids on the tensile properties of [(±45)4/(0,90)/(±45)2] S and [(±45)/0 4/(±45)(0,90)] S composites.Specimens with void contents in the range of 0.4% to 9.0% were fabricated from carbon/epoxy fabric.The void content was determined by ultrasonic attenuation and optical image analysis,and microscopic inspection was also used to analyze the shape and size of the voids.The influence of voids on the tensile strength and modulus of both stacking sequence is compared in terms of the size and the shape of the voids.The effect of voids on the initiation and propagation of tensile failure of both stacking sequence composite was investigated. 相似文献
1000.
高慧莹 《电子工业专用设备》2011,40(7):1-6
从材料特性出发,分析了氮化镓基LED用衬底材料的性能需求,主要分析了蓝宝石和碳化硅衬底在LED制作中的应用,并描述了当前的发展状态以及未来的发展趋势。 相似文献