Papers by Author: Guo Qiang Luo

Abstract: Aluminum (Al) and Copper (Cu) have been used in graded density impactors. Al-Cu composites with different compositions have been prepared by hot pressing sintering. Intermetallic compounds were produced when the temperature was above 723 K, while they can’t be found at the temperature of 723 K. The relative density of Al-Cu composites from pure Al to pure Cu consolidated at 723K all exceeded 98.5%. The optimum sintering conditions were then determined to sintering temperature of 723 K, uniaxial pressure of 100 MPa, and duration time of 2 h. Al and Cu were mixed homogeneously and well compacted, and no obvious pores were found. The thickness of diffusion layer between Al and Cu was very thin, only about 0.6 μm. The wave impedance values increased almost linearly from 16.98×10⁶ to 40.66×10⁶ kg/m²·s with increasing Cu content in Al-Cu composite from 0 to 100 vol.%, which was well consistence with the values calculated according to the rule of mixtures. The elastic modulus of different compositions matched well with the theoretical model of Voigt and Reuss. Highly densified Al-Cu composites without intermetallic compounds were successfully prepared using hot-pressure sintering, which was the basis of fabricating Al-Cu system graded density impactors.

Abstract: The CNTs/PMMA Nanocomposite Foams Are a Kind of Novel Multifunctional Foams which Have a Potential Application for Lightweight Conductive and EMI Shielding Materials. In this Work, the CNTs/PMMA Nanocomposite Foams with Different CNTs Contents from 1wt.% to 10wt.% Were Prepared at a Temperature Range of 50-140 °C with Supercritical Carbon Dioxide as Blowing Agent. The Results Suggest that the Fully Heterogeneous Nucleation Is Achieved due to the Contribution of Well-Dispersed CNTs in PMMA. The CNTs/PMMA Nanocomposite Foams Exhibit a Uniform Cell Distribution, and the Cell Density Is Two Orders of Magnitude Higher than that of PMMA Foams. The Cell Size and Cell Density of CNTs/PMMA Nanocomposite Foams Could Be Controlled by Adjusting the Foaming Process and CNTs Contents. It Is Also Suggested that the Foaming Process Plays an Important Role on the Cell Structure Rather than that of CNTs Content when it Is Higher than 1wt.%.

Abstract: Spark plasma sintering (SPS) is a newly developed technique that enables poorly sinterable tin oxide powder to be fully densified. Sintering without sintering aids is of great importance when SnO₂ ceramics are used as electrodes in the glass melting industry and aluminum electrometallurgy. Dense and good-conductive Antimony-doped SnO2 ceramics can be achieved by SPS at a lower sintering temperature and in a shorter time. When the Sb₂O₃ concentration is 1.0 mol%, the densities of the samples reach their maximum value, which is 98.2% of the theoretical value. When the content of Sb₂O₃ was 2.44mol%, SnO₂ ceramics with densities 97.6% can be obtained at 800°C-1000°C, and the resistivity was about 5.19×10^-2Ω.cm at the sintering temperature of 1000°C. Defined amount of Sb³⁺ used in our research are beneficial to low the sintering temperature and promote the densification of SnO₂ ceramics

Abstract: In this study, SnO2-based ceramics, with CuO as sintering aid and Sb2O3 as activator of the electrical conductivity, was obtained by pressure-less sintering at 1100°C ~ 1470°C. Addition of antimony leads to a higher densification temperature. Densification behavior and microstructure development are strongly dependant on CuO and Sb2O3. CuO gives rise to a liquid phase; Sb2O3 retards the formation of liquid phase and hinders the growth of grain. The electrical resistivities of SnO2-based ceramics vary in a wide range from 10-2 to 107 Ω•cm, depending on starting compositions and processing conditions. The electrical resistivities of samples with different amounts of CuO and Sb2O3 show different trends with the increasing of sintering temperature. The addition of antimony rapidly promotes electrical conductivity of SnO2-based ceramics containing CuO as the solid solution reaction of Sb2O3-SnO2. As the additions of CuO and Sb2O3 are the same, the electrical resistivity arrives the minimal value of 4.72×10-2 Ω•cm for 99%SnO2+0.5%CuO +0.5%Sb2O3 at 1470°C. More content of Sb2O3 than CuO causes the degression of density and the rising of electrical resistivity of ceramics.

Abstract: Tape casting was used for the preparation of Mg-Cu systems density graded materials. A series of tapes with uniform compositions ranging from 100wt% Cu to 100wt% Mg were fabricated with sufficient strength to be handled during the post-processing stage. The effect of the tape casting process parameters on the properties of the tape were studied, such as the composition of the Mg-Cu and the solid loading. The rheology of the slurry of different Mg-Cu composition for tape casting was characterized by viscosity. The tapes characterized by microstructure, thickness and bulk density were outlined. The results demonstrated that the different Mg-Cu composition slurry with well-dispersed, high stability, certain solid loading from 45 ~70 wt% were obtained. The viscosity of the slurry and the density of the green tapes were increased with the increasing of the content of Mg. The thickness of tapes of compositions ranging from 100wt% Cu to 100wt% Mg with certain strength could be achieved 68-110μm and the density of the tapes was 0.74-2.42g/cm3. For 100wt% Cu tapes, when the solid loading was 68wt%, the high density tape was produced. The tapes with different thickness, density and different Mg-Cu compositions were obtained.

Abstract: FGMs with density gradient are of great interest in field of dynamic high-pressure physics. In this paper, tungsten particles reinforced epoxy resin composites, and FGMs with density gradient were prepared by calendering technique. Microstructures of tungsten-epoxy composites with various tungsten contents were analyzed, and the density distribution of the FGMs was characterized. The results show that the distribution of tungsten particles in tungsten-epoxy composites is homogeneous, and the combination of tungsten particles with epoxy matrix is good. The density of tungsten-epoxy composites varies from 1.26gcm-3 to 4.0gcm-3, and the thickness of each layer is about 200μm. Tungsten-epoxy FGMs with density gradient were obtained by laminating thin layers of tungsten-epoxy composites with different tungsten contents. The highly enough bonding strength between these transition layers and good parallelism were achieved. The density distribution of the tungsten-epoxy FGMs can meet the demand of the power function equation of density and thickness.

Abstract: The preparation of 50Mg/50Cu composite by tape casting and hot-press sintering was studied. During the preparation of the slurry and tapes, the effects of different organic additives were discussed and the contents of the organic additives were optimized. Then the sintering temperature of the green samples were discussed to get densified 50Mg-50Cu samples. The slurry was characterized by viscosity. And the tapes and the final 50Mg-50Cu sample were anaylsed by density, XRD and SEM. The viscosity results indicated that the slurry with well-dispersed and stable properties for tape casting could be obtained. The solid loading of the slurry is 48wt%. After tape casting, the density and uniform tapes were made. The XRD and SEM results demonstrated that the optimal sintering temperatures of Mg-Cu composite were from 460°C to 470°C.

Abstract: Functionally graded material (FGM) with density gradient has showed great potentials as flier-plate for creating quasi-isentropic compression waves. In order to obtain a FGM with low density in the front face and with a wide density range, the Mg-W system gradient material is designed, and the power metallurgy method and hot-press (HP) sintering are chosen for its fabrication. The sintering of Mg-W alloys is studied at relative low temperatures and the processing of densification is mainly investigated. It is found that, up to 85wt%W, the approximately wholly dense Mg-W system alloys are achieved at 620°C for 1.5 hours under a pressure of 100MPa. Mainly the mechanical mixtures of Mg and W are formed in Mg-W alloys. And the Mg-W alloys are fully densified at 620°C due to the conglutination of Mg, a small amount of which are melting in this experimental condition. Finally, the Mg-W system FGM with a wide density gradient from 1.74g/cm3 to 7.56 g/cm3 within the 3.50mm thickness range is fabricated at the sintering parameter of 620°C-100MPa-1.5hours.

Abstract: TC4-LY12 welding joint are fabricated by vacuum diffusion welding. The bonding phases are confirmed by X-Ray Diffraction (XRD), the morphology of samples and chemical composition are evaluated by Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectrometer (EDS) analysis, the mechanical property is tested by tensile strength measurement. The XRD patterns show that the main intermetallic compounds formed in the transition zone are Ti3Al, TiAl and TiAl3. Combining the fracture surfaces morphology and element analysis, the bonding mechanism of TC4-LY12 joint is attributed to the inter-diffusion between Ti and Al atoms. The initial phase formed during the reaction is TiAl3 due to the diffusion of titanium atoms into aluminum substrate; with the process of the reaction, Ti3Al and TiAl phases appear gradually with the atomic ratio of 1:1.The tensile strength of the joint increases remarkably with increase of temperature and takes a maximum value (~60MPa) when the welding temperature is 550°C.

Abstract: A new kind of functionally graded materials (FGM) with density gradient has come to show great potentials as flier-plates for creating quasi-isotropic compression waves. In order to meet the demand of lower density in the front face and wider density range for such flier-plate, Mg with a density of 1.74g/cm3 and W of 19.3g/cm3 are selected to make Mg-W system density graded materials. Mg-W alloys with various mass fractions of Mg and W were sintered by spark plasma sintering (SPS) technique at low temperatures, and the processing of densification is mainly investigated. It is found that, up to 92wt%W, the Mg-W alloys can be fully densified at 873K due to the conglutination of Mg particles. The Mg-W alloys still exist as a mechanical mixture of Mg and W. Finally, the Mg-W density graded materials with a density change from 1.74g/cm3 to 10.55g/cm3 have been successfully prepared.