Advanced Materials Research Vols. 217-218

Abstract: Ca3Ru2O7 is new tpye of thermoelectric materials.A theoretical study is presented for the stability, electronic and magnetic properties of three phases of this new thermoelectric materials in the framework of density functional theory (DFT). The calculated cohesive energy is -7.94eV/unit. AFM2 are less stable than other pahses. Electronic calculations indicate that Ca3Ru2O7 is metallic in nature. The covalent bonds in these structures are due to orbital overlap between p bands of O and d bands of Ru, and DOS at Fermi level are dominated by d bands of Ru. FM phase have obvious magnetic moments.

Abstract: The First-principles based on plane-wave pseudo-potentials methods was applied to investigate the lattice parameter, electronic structure and optical property of pure Si doped with transition metal. The calculation result show that the lattice parameter decrease for Si doped with Cr and therefore the more stable structure, Si doped with Sc, Ti, V have opposite trend. Hybrid and electron transfer display intensely for Si doped with Cr from that with Sc, Ti, V. the absorption peak is located at the region of 2.42eV-2.80eV and the absorption coefficient increase intensely for doped Cr system.

Abstract: 3wt% graphite/copper matrix composites had been prepared after mechanical ball milling, pressing, vacuum hot pressed sintering and hot extrusion. With tensile test, hardness test and impact test, utilizing material testing machine, Vickers hardness tester, impact machine, optical microscope and scanning electron microscopy, effect of milling time on mechanical property of graphite/copper matrix composites had been investigated. The results show that after mechanical milling and hot extrusion, microstructure had been refined, distribution of graphite phase and cohesion between copper and graphite had been improved, mechanical locking force between copper matrix and graphite, tensile strength and hardness of composites had been increased. Elongation percentage and impact absorption work are less resulting from work-hardening during ball milling.

Abstract: To provide reference for choosing technological parameters of subsequent powder densification, thermal stability of 3 h-milled 3 wt% graphite/copper nanocrystalline composite powders were investigated with such analytical methods as scanning electron microscopy (SEM), back-scattered electron images and X-ray diffraction (XRD). The results show that diffraction peak of graphite in XRD pattern is absent because of too small graphite particle. No major variation of grain size of Cu with annealing temperature is observed. Accumulation and growth of graphite phase aren’t seen. The microhardness is nearly constant for the annealed powders. Therefore, 3 h-milled 3 wt% graphite/copper nanocrystalline composite powders possess good thermal stability.

Abstract: The software of finite element simulation DEFORM-3D was used to simulate the extrusion process of the large diameter thick wall seamless steel tube, and the effective stress and load curves were analyzed in the situation of different concave die mould cone Angles. The simulation results show that with the increase of deformation degree, the effective stress and load of the blank increased gradually first and then reached a plateau. With the increase of the concave die mould cone Angle, the load of top die decreased.

Abstract: Employed DEFORM software to simulate vertical extrusion of large diameter thick-walled pipe, by using the Finite Element Method in the three-dimensional modeling software Pro/E of the CAD platform. Analyze the law of blank flow in extrusion process, distribution of stress and strain, and the influence of different extrusion ratio on deformation of thick-walled tube comparatively.

Abstract: In power station big caliber thick wall seamless tube typical steel P91for example, The hot deformation behavior and heat flow stress-strain curve of the heat resistant steel P91was investigated with a compression test on Gleeble3500 simulator at a temperature range of 1050°C～1200°C and strain rate range of 10-4～5s-1. The test curve shows that P91 materials have the dynamic recrystallization and recovery behavior in high temperature and deformation. With the rise of temperature and strain rate of decreased, flow stress is lower and the dynamic recrystallization phenomenon is easier to occur. By metalloscope observed, in the high temperature and low strain rate conditions, the dynamic recrystallization area and new nucleation grain size are larger, and microstructure is more uniformly distributed.

Abstract: Considering the difference of 3 dimension interface topography unit, the distribution of residual stress in thermal barrier coating was calculated using ABAQUS soft by finite element method. The calculating result shows that the residual stress is affected by interface topography unit obviously. Compressive stress exists in concave topography unit and tensile stress in convex topography unit. Stress concentrates in boundary of topography unit and reaches maximal value at the lowest and the highest place of concave and convex topography respectively. Compressive and tensile stress change with the size of topography unit distinctly.

Abstract: Sn-37Pb solder alloys doped Ni, Al and Cr separately were prepared, and the effect of trace doped elements on the surface film structure of Sn-Pb liquid solder alloys was studied by X-ray photoelectron spectroscopy (XPS). The results showed that the surface of Sn-37Pb liquid alloys was mainly SnO2 and PbO after oxidizing and laying for five minutes at 250°C, and the enrichment of trace Al and Cr was on alloy surface, but the enrichment of trace element Ni was not obvious. The surface oxidation film of Sn-Pb liquid solder alloys was become denser after adding 0.05wt% Ni or Al, which will reduce the growth rate of oxidation film. The thickness of oxidation film was only one-fifth of its original under experimental conditions. However, the oxidation film was become looser after adding trace 0.05wt% Cr, the growth rate was accelerated, and the thickness of oxidation film was increased to two times of its original. Trace Ni and Al were characterized with selective oxidation on Sn-37Pb alloys surface.

Abstract: According to mechanical characteristics of welded turnout on continuous-slab-track and bridge, an integrated turnout/track slab/beam/pier finite element model was established to analyze the interaction between welded turnouts on continuous-slab-track and bridge. The study focused on No.18 turnout (60kg/m rail) with movable frog being laid on a (32+48+32) m continuous beam, expansion additional force and braking additional force of the turnout were calculated when the temperature dropped. The results show that the longitudinal interaction between welded turnouts on continuous-slab-track and bridge is small, which presents a reasonable structure type of welded turnout on bridge; in calculation of the expansion force, when the temperature drops, the shrinkage and creep of the base-slab and longitudinal stiffness reduction caused by the cracking are considered, so the results are more representative than those from the case of rising temperature. Therefore, the case of temperature dropping should be the main concern in design; under the action of the braking force, stress and deformation of each component within this turnout/bridge system are comparatively large.