Advanced Materials Research Vols. 26-28

Abstract: Full-potential linearized augmented plane-wave (FP-LAPW) method within the local density approximation plus self-interaction correction (LDA+USIC) has been applied to study the structure stability and electronic structure of ReSi1.75 and its doped systems with Al and Mo. Structural relaxation results show that the vacancy prefers to occupy the Si3 and Si4 site in the lattice with little ordering. For doping systems, Al prefers to substitute for Si at the Si3 site and Mo prefers to substitute for Re at the Re1 site. ReSi1.75 shows narrow gap semiconductor behavior with an indirect gap of 0.12 eV and a direct gap of 0.36 eV. Al doping compound remains semiconductor while Mo doping compound has a tendency to change into semimetals or metals. The Fermi level of doped systems moves into the valence band resulting in an increase of density of state at the Fermi level. It will enhance the thermoelectric properties and agrees well with the experiment results.

Abstract: The dynamic globularization behavior during hot working of Ti-6Al-4V alloy was investigated by high temperature torsion tests. The torsion tests were carried out to investigate microstructure evolution occurring during dynamic globularization in Ti-6Al-4V alloy. The torsion tests were performed under a wide range of temperatures and strain rates with true strain up to 2. The flow curves revealed that the amount of flow softening for the fine alpha-lamellae structure was higher than that for the coarse alpha-lamellae structure under the temperature of 900oC. The effects of hot deformation parameters and initial microstructures on the dynamic globularization were analyzed.

Abstract: Based on the measured CCT diagram of steel S34MnV, the parameters for the heat treatment of large marine crankthrow were designed, and the models for predicting microstructural evolution and mechanical properties were developed. By computer simulation, the temperature and phase volume evolutions in the controlled cooling process were predicted together with the final mechanical properties. Finally, the manufactural trial was carried out in heavy plant, the temperature evolution and final mechanical properties on the blank were obtained. The manufactural data agree well with the predicted results.

Abstract: The technology of computer numerical simulation on casting process is an important frontal field of material science and technology. The numerical simulations of camera shell in the pressure die casting process were carried out. The distributions of temperature and solidification time in the filling process were obtained. Based on the simulated results and the Niyama criterion G/ R , the positions of slack were predicted, which were agreement with the practical result. Consequently, an improved scheme was presented, in which the workpiece defects were obviously reduced. So it’s significant for the application of numerical simulation on improving the quality of the casting, shortening the period of producing, reducing the cost and guiding the engineer for taking reasonable method to optimize the technological design.

Abstract: This paper presents experimental and numerical simulation for deformation and fatigue life prediction of various cables, such as electrical, optical and network cables. The cable damage is produced by the tensile, bending and torsional action under moving and fixing condition, and by direct external impact. To obtain material responses of the cable, uniaxial tensile tests and drop-weight impact tests were adopted, and the nonlinear constitutive equations based on various strain energy potentials or material models were employed to analyze deformation of polymer sheath and metallic armor layer of the cable. Finite element results were compared with experimental data for deformation and impact absorption energy of the cable during direct external impact. Also, fatigue strength of the cable was predicted from variation of calculated stress level under tensile conditions. Fractured surface of the cable were analyzed by scanning electron microscopy (SEM).

Abstract: In this study, numerical analysis applying the finite element method (FEM) was used to investigate the effect of heat flux and temperature on thermal strain of aluminum alloy casting mold. For numerical analysis, analysis model was considered the effect of shrinkage, rapid temperature variation on the casting mold and was applied the temperature calibration to reduce the deformation and stress by temperature difference of inside and outside the mold during the cooling process. In detail, temperature, deformation and stress distributions occurred inside of casting mold predicted by numerical method and then investigated the correlations between the heat flux and temperature variation during the cooling process. As a result, aluminum alloy casting mold is occurred deformation and stress because of rapid temperature difference in the initial of cooling, but it can be reduced the thermal strain through the heat flux control and temperature calibration. Accordingly, the technique of this numerical study will be helped to make the effective and the good quality of casting mold products.

Abstract: In this research, the effect of microstructure on the mechanical properties of tungsten heavy alloys is discussed. The tensile properties of tungsten heavy alloys are found to be dependent on volume fraction of W, contiguity and grain size of W particle. The ductility is found to be influenced by contiguity and connectivity. The volume fraction of matrix increases sharply with the increase in rare metal oxide impurity, which adversely affects the mechanical properties of tungsten heavy alloys.

Abstract: Thermal, electrical and mechanical properties of high purity niobium and tantalum refractory rare metals were investigated to evaluate the physical purity. Higher purity niobium and tantalum metals showed lower hardness due to smaller solution hardening effect. Temperature dependence of electrical resistivity showed a typical metallic behavior. Remarkable decrease in electrical resistivity was observed for a high purity specimen at low temperature. However, thermal conductivity increased for a high purity specimen, and abrupt increase in thermal conductivity was observed at very low temperature, indicating typical temperature dependence of thermal conductivity for high purity metals. It can be known that reduction of electron-phonon scattering leads to increase in thermal conductivity of high purity niobium and tantalum metals at low temperature.

Abstract: The long-term corrosion resistances for the carbon steels have been investigated under high temperature pressurized water atmosphere, in the conjunction with the analysis of nondestructive properties by the ultrasonic wave. The corrosion test for carbon steels was carried out at the temperature of 200 °C under a water pressure of 10 MPa. The corrosion test cycles for carbon steels were changed up to 65 weeks. The mechanical properties of carbon steel suffered from the corrosion cycle were investigated by a tensile test, attaching an acoustic emission sensor on the test sample. The tensile strength of carbon steels greatly decreased beyond the corrosion cycle of 35 weeks, accompanying the increase of weight loss by the creation of corrosion damages. The attenuation coefficient of carbon steels by the ultrasonic wave increased with the increase of corrosion cycles.

Abstract: Steam generator tubes provide the pressure boundary between the primary and secondary regions of a nuclear power plant. Alloy 600 is a tube material with good corrosion resistance; however, tubes of this material have experienced damage, particularly as Stress Corrosion Cracking, under the elevated temperature and pressure environment of a nuclear power plant. These damaged tubes must be repaired to prevent leakage of radioactive material from the primary to the second regions in the nuclear steam generator. In this study, Ni-P-Nano TiO2 and ZrO2 layers were produced by pulse electroplating for steam generator tube repair. These electroplate layers were obtained from Ni sulfamate bath with an added small quantity of H3PO3 and Nano TiO2 and ZrO2 particles with an average size of 20-80nm. Results of TEM analysis in these layers show that Nano TiO2 and ZrO2 particles were uniformly distributed into the electroplated Ni matrix and the tensile strength of these layers at 800-1000MPa was higher than that of alloy 600 with a conventional pure Ni electroplate layer.