Advanced Materials Research Vols. 97-101

Abstract: Bi-Pb-Sn-Cd metal particles were fabricated with dispersant sodium oleate by phase inversion method. The effects of dispersant content, temperature, and stirring speed and the average size of Bi-Pb-Sn-Cd metal particles were investigated by scanning electron microscope and particle size distribution analyzer. In addition, the preparation mechanism was preliminarily discussed. Finally, the optimized preparation conditions were determined and well-dispersed superfine Bi-Pb-Sn-Cd particles with average diameter of about 0.3μm were obtained.

Abstract: The structure and property of Ce-doped Ba0.2Sr0.8TiO3 (BST) were investigated as a function of Ce content. The density experiment results confirmed that increasing the Ce doping ratio caused the decrease in shrinkage factor of BST in the sintering procedure. Additionally, both Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) analysis showed that the grain size of Ce-doped BST was dependent on the Ce content. Further more, the dielectric constant and dielectric loss had a curve relationship with increasing Ce content. The improvement of the electrical properties of Ce doping BST may be related to the decrease in the concentration of oxygen vacancies. According to the research, the diameter of grain, the dielectric constant and loss factor of the 1mol% Ce-doped Ba0.2Sr0.8TiO3 were 500nm, 365.8 and 0.0063, respectively.

Abstract: Ti(C, N)-based cermet and functionally gradient Ti(C, N)-based cermet were prepared by vacuum sintering and post surface heat-treatment in nitrogen, respectively. Tribological behaviors of obtained cermets were comparatively studied. Dry sliding wear and cutting test were conducted against quenched medium carbon steel. It was found that a graded structure formed and the surface hardness of functionally gradient Ti(C, N)-based cermet was improved. Friction coefficients of both cermets decreased with the increase of the sliding speed. The friction coefficient of Ti(C, N)-based cermet was lower than that of functionally gradient Ti(C, N)-based cermet at the conditions of higher sliding speed and higher load. The cutting test demonstrated that Ti(C, N)-based cermet exhibited better cutting performance and higher wear resistance than the cemented carbide YT15, cermet TN20 and functionally gradient Ti(C, N)-based cermet, while the functionally gradient Ti(C, N)-based cermet exhibited a similar performance as YT15 and TN20.

Abstract: Calcium aluminate and Fe-Si alloys were successfully synthesized by using red mud and aluminate dross as the main raw materials in the lab-scale experiment. Three apt experimental parameters were obtained: 1.2 times of theoretical addition amount of aluminum dross, binary basicity of raw materials 0.9, 40min smelting time. The chemical compositions of calcium aluminate synthesized meet the standard of CA-60 cement of China, and the calcium aluminate can be used as pre-melted-slag in Steelmaking process.

Abstract: In this work, a new severe plastic deformation technique for preparing bulk fine-grained materials has been developed to achieve higher plasticity of powder materials. This novel technique, named Equal Channel Angular Pressing and Torsion (ECAPT), combines two severe plastic deformation methods: equal channel angular pressing and twist extrusion. With the designed ECAPT set-up, pure Al powder particles were successfully consolidated into full dense bulk material with fine grains at a lower deformation temperature (200°C) by Powder in Tubes-Equal Channel Angular Pressing and Torsion (PITS-ECAPT). After two passes of PITS-ECAPT, the microstructures at X, Y and Z planes of each sample were all sheared and elongated along a certain direction with fine banded structures; the grains were greatly squashed and refined with an average grain size of ~ 11.90µm; the deformed sample reached the full density; the micro-hardness and yield strength achieved 49.9kg/mm2 and 155Mpa respectively, which were significantly higher than those of as-cast annealed pure Al and pure Al powder sintered materials.

Abstract: An experimental study of co-injection molding which involves sequential injection of dissimilar metal feedstocks into a mold has been carried out. The effect of skin temperature and injection velocity on the material distribution of co-injection molded plates has been studied. It was found that the molding temperature was important in controlling skin-core distribution, while injection velocity seemed to play no significant role. The experimental results were analyzed by taking account of the relative viscosity of the two melts. It was demonstrated that the differences in rheological properties of the metal feedstocks involved are the primary variable determining the phase distribution of the molded parts.

Abstract: In this study, numerical calculations of fatigue-creep interaction behavior for powder metallurgy materials with inclusion was carried out based on the Kachanov-Rabotnov damage law. The emphasis was placed on the influence of different fatigue cycle times and shape of inclusion on matrix damage for a constant of creep time. The results show that the creep damage law can be used to study the fatigue-creep interaction behavior of PM materials. And the creep damage increases with the fatigue cycle times increasing. The shape of inclusion remarkably influences the damage of matrix. Generally, elliptical inclusion causes much more damage to the matrix than the round inclusion.

Abstract: A model for designing sandwich nanocomposite ceramic tool materials with symmetrical distribution was presented. By adding nano-sized Al2O3 particles into the submicro-sized Al2O3 and TiCN, Al2O3/TiCN sandwich nanocomposite ceramic tool materials were fabricated by means of powder-laminating and hot-pressing technique. The experimental results showed that optimal mechanical properties were achieved for the composite with the addition of 35 vol.% TiCN particles in the middle layer and 45 vol.% TiCN particles in the outer layers, layer thickness ratio is 0.3, with the flexural strength reaching respectively 900MPa，fracture toughness and Vicker's hardness in the surface layers being 6.5MPa•m1/2 and 19.2GPa.

Abstract: Carbon foam with relatively high compressive strength and high porosity was prepared from a mixture of mesophase pitch and Si particles by foaming and carbonization. The influence of Si content on the microstructures and properties of the carbon foam was studied. Results show that the pore number decreases and the strut thickness increases with an increasing of Si content. In addition, bulk density also increases with increasing Si content but the porosity decreases. Si addition to the mesophase pitch reduces the number of microcracks on the cell wall of the carbon foam remarkably which results in an increase of compressive strength for the carbon foams. Compressive strengths improve by 46%, 176% and 339% at Si additions of 30%, 40% and 50% (wt %), respectively. Carbon foam with a relatively high compressive strength of 24.6 MPa and a porosity of 61% are obtained when 50 wt% Si is added.

Abstract: The Cu-based friction material with Ni coated nanometer SiO2 (Ni/n-SiO2) particles was prepared by the powder metallurgy technology. Friction properties of the friction materials were evaluated by a friction tester. The microstructure and worn morphology were characterized by optical microscope (OM) and scanning electric microscope (SEM). The results indicate that the microstructure is uniform. The Ni/n-SiO2 particles can enhance the wear ability of Cu-based friction materials. The wear rate of the friction material with Ni/n-SiO2 is 6.58 times of that without Ni/n-SiO2. The main wear mechanisms are abrasive wear and adhesive wear, and Ni/n-SiO2 particles can reduce the abrasive wear and adhesive wear.