Microstructural selection during the directional solidification (DS) of Ti-47Al grown from a Ti-43Al-3Si seed was studied. The high-temperature hexagonal close packed α-phase in a cellular growth condition were correctly oriented so that the DS ingot with fully lamellar microstructure parallel to DS direction was successfully obtained at growth rate of 90mm/h. As the liquid composition closed to Ti-47Al, because of the variation of growth rates and the effect of solidification interface morphologies on solute segregation, βphase started to nucleated and grown in the interdendritic of α phase, lamellar microstructures inclined with angles of 45º to the growth direction were grown, thus successful seeding from the Ti-43Al-3Si seed was interrupted. Fine α dendritic in preferred crystallographic direction were obtained when the growth rate increased to 720mm/h.

The surface morphologies of Cu thin films deposited by magnetron sputtering were obtained by atomic force microscopy (AFM). From AFM images, power spectrum density (PSD) and roughness measurement methods were proposed to obtain dynamic scaling exponents of the film surface evolution. The results show that the film surface evolution has multi-scale characteristic. The global roughness exponent and growth exponent are 0.83 and 0.85, respectively, whereas the local roughness exponent and growth exponent are 0.88 and 0.26, respectively. The local dynamic surface evolution is consistent with that predicted by surface diffusion-dominated growth model. The global surface dynamic evolution exhibits anomalous scaling characteristic, which arises from bulk diffusion mechanism during the films grown at high temperature.

Cahn-Hilliard equation coupling with thermodynamic data is solved by Fourier transformation spectrum method due to the high efficiency and accuracy to simulate particle growth and Ostwald ripening for Cu-Pb monotectic alloy at the isothermal condition. The simulation results show that particle growth and Ostwald ripening for specific Cu-Pb monotectic alloy can be realized by the adjustment of gradient coefficient and mobility ratio. The growth of singular nucleated particles in a supersaturated matrix depends on the adjustment of free energy function and the smaller gradient coefficient, the more distinct steepness of concentration profile is. Growth rate of particle radius is in good agreement with the well accepted Zener’s law. Size distribution of reduced particle radius is computed and the peak of radius distribution changes from approaching the average radius to exceeding it.

The initial morphology and mean orientation of columnar-grains of pure copper was obtained by electron backscattering diffraction (EBSD). A finite element model based on crystal plasticity was established to simulate the orientation and deformation band evolution of individual grain during uniaxial compression. Corresponding compression test was carried out to obtain experimental data which showed the actual evolution of orientation and band morphology in the polycrystalline sample. A series of statistical results of grain orientation evolution were obtained, and the calculated results were compared to experimental data.

Microstructures and mechanical properties of AZ91 magnesium alloy after homogenized, hot extrusion and succedent aging are investigated. The results show that dynamic recrystallization occurs during extrusion at elevated temperatures of 320℃ and 380℃; compared to the as-cast alloy, microstructures of the extruded AZ91 alloy are refined, and the mechanical properties are enhanced remarkably; succedent aging is helpful to improvement of mechanical properties of the extruded AZ91 alloy. In this experiment, the ultimate tensile strength of the AZ91 alloy extruded at 380℃and aged at 200℃×10h is about 357MPa, and the elongation of the alloy reaches about 8%.

Rapid directional solidification experiments were carried out with Al-Pb alloy. The microstructure evolution during the solidification was calculated according to the practical experimental conditions. The results indicate that, under a constant solidification velocity, the size and its distribution width of the minority phase droplets increases with the Pb content of the alloy. For an alloy of given composition, the size and its distribution width of the minority phase droplets decreases with the solidification velocity. The numerical results, which have an acceptable coincidence with the experimental ones, show the microstructure evolution process clear.

The hot deformation behavior of NiTi alloy was studied by compressive deformation tests in the strain rate range 0.001-10s-1 and temperature of 700-900℃, and associated structural changes were investigated by observations of metallography and TEM. By using regression analysis methods based on measured data, the material parameters of the Arrhenius-type hyperbolic-sine equation were resolved, and then fitted against deformation strains. Based on the above analysis, a constitutive equation which related the flow stress to temperature, strain rate and strain was established. The activation energy, Q, and lnA, decrease as the strain increases. However, the stress exponent, n, linearly increases with the increase of the strain. The main reasons that lead to the difference between the true stress-true strain curves of NiTi alloy and those of non-intermetallic materials are reciprocal order-disorder transition and dynamic recovery or dynamic recrystallization.

Isothermal compression has been carried out at a Thermecmaster-Z simulator. According the analysis of experimental results, the peak and steady stress significantly decreases with the increasing of the deformation temperature and the decreasing of the strain rate, and the deformation temperature would also affect the critical value of strain to reach the steady flow at the high temperature deformation of the nickel-based GH4169 superalloy. Meanwhile, a model for flow stress of the nickel-based GH4169 superalloy at high temperature deformation has been established in terms of the fuzzy artificial neural network. The maximum difference between the calculated and the experimental results is 10.18%, the average difference is 2.11%. The calculated precision is better than those through the regression method.

The transformation characteristic, microstructure and micro-hardness for ultra high-strength pipeline steels with different content of Mo and B as well as different Mo/B ratio were investigated in this paper. Combined additions of Mo and B were found to more effectively increase the hardenability of the steel than the individual effectiveness of these two elements, which increase the volume fraction of bainite in microstructure and enhance the hardness of the steel. The experimental results showed that there should be an optimum Mo/B ratio to achieve the optimum microstructure and mechanical properties of the steel. The mechanism for the combined Mo-B effect on ultra high-strength pipeline steels was also discussed.

The microstructures and aging characteristics of 7050 aluminum alloy plates extruded from low frequency electromagnetic casting and DC casting ingots have been studied. The results show that the plate extruded from LFEC ingot has a fine microstructure. After a constant extrusion process, the average diameter of grains of the plate extruded from LFEC ingot is about 10μm, and the plate extruded from DC ingot is about 20μm. Comparing with plate extruded from DC ingot, the plate extruded from LFEC ingot has a fast aging rate and much stronger ability of aging strengthening. Aging at 120℃, the plate extruded from LFEC ingot reaches its peak strength in 8 hours, and its longitudinal and the transverse strength are 656MPa and 596MPa respectively. However, the plate extruded from DC ingot reaches its the maximum value in 12 hours and its longitudinal and the transverse strength are 647MPa and 590MPa respectively.

The 7050 aluminum alloy ingot with fine microstructure was cast by low frequency electromagnetic casting (LFEC) process. The homogenization treatment behaviors of LFEC ingot were investigated experimentally. The results show that the ingots cast with low frequency electromagnetic field has a better homogenization effect than conventional DC ingot. Under the same homogenization condition, the LFEC ingot has fewer low melting point phase between grains and more solute elements inside grains. After homogenized for 12 hours the LFEC ingots can reach the average percentage of the alloy elements, but the DC ingots haven’t reach it until for 48 hours.

The microscopic creep and damage evolution under elevated-temperature tension was simulated using crystalline thermo viscoplastic constitutive description for the γ-matrix and γ'-precipitates respectively. In the present paper, the following contents were introduced: (1) a Representative Volume Element(RVE) of Voronoi aggregate with randomly spatial arrangement of γ-γ' phases; (2) a single crystalline thermo viscoplastic constitutive relation associated with micro-void damage description and corresponding iterative algorithm; (3) damage evolution of γ-γ' superalloy at micro scale under elevated temperature; (4) comparative analysis of describing ability between two type of RVEs of Voronoi γ-γ' aggregate and roughly-periodic γ-γ' unit cell.

The effect of rare earth oxide (La2O3) contents on direct laser sintering of WC-10Co particulate reinforced Cu matrix composites was investigated. It shows that using an optimal La2O3 content of 1.0% can refine the laser sintered structure, homogenize the dispersion of reinforcing particulates and improve the particulate/matrix bonding coherence, leading to a high densification of 96.3% theoretical density and a high microhardness of HV0.1403.1. However, an excessive addition of La2O3 above 1.5% results in a decrease in the laser sintering ability. The metallurgical mechanisms of rare earth element in laser sintering of particulate reinforced metal matrix composites were discussed.

The corrosion electrochemical behavior of a silane coating with flaked Zn-Al powder on carbon steel was studied in 3.5％ NaCl solution using open circuit potential monitoring, potentiodynamic polarization, electrochemical impedance spectroscopy(EIS) and scanning electron microscope(SEM). The results indicated that the process of deterioration of the coating presented three stages with immersion. At the initial stage, the flaked zinc powder on the surface layer of the coating started to activate with the attack of the electrolyte; the middle stage showed the feature of electrochemical protection of the coating for the substrate; and the barrier protection of the coating predominated in the last stage. The middle stage lasted a long period while the third stage had a short time, suggesting a strong cathodic protection and a weak barrier mechanism of corrosion prevention of the silane coating with zinc and aluminum powder.

The inhibitive effect of G105 steel was studied in 31(wt)% NaCl solution based on new compound inhibitor including ZnSO4, CaGL, APG, Na2SiO3, Na2WO4. And inhibitory mechanism was analyzed by polarization curve and EIS. Kramers-Kronig transforms have been developed to apply the in the analysis of experimental electrochemical impedance data. XRD and EDS were carried out to examine corrosion products formed on the surface and adsorbed inhibitor. The results showed that compound inhibitor was mixed-type inhibitor and the inhibition efficiency was above 80% at 80℃. The impedance data do not satisfy Kramers-Kronig transforms. Corrosion product was mainly Fe3O4, content of elements in inhibitors filmed on electrode surface increased with concentration of inhibitors.

The effect of electromagnetic vibration on the distribution and morphology of primary silicon in the Al-18wt%Si alloy has been investigated systematically in this paper. The experimental results show that the primary silicon agglomerated and expelled to the top of the sample when the magnetic intensity is low(2T). The ssegregation of silicon grains decreased gradually and the phenomenon of agglomerating disappeared with the increase of magnetic intensity (10T), and the star-like coarse primary silicon turned refined flake or square. It is shown that the movement of primary silicon is depended on gravity and the effective viscous force caused by the magnetic field，and the terminal migration velocity is proportional to the radium of primary silicon and inversely to the intensity of magnetic field. The observed results are approximately agreed with the theoretical analysis.

Some parameters such as length of the top half of mold, coil location and meniscus level in the two-stage slitless soft contact mold were analyzed through the 3-D FEM numerical simulation method. The distribution of electromagnetic field in the whole two-stage slitless mold system was also studied. Magnetic flux density in mold increased with the length of the top half increasing. Coil should be placed near the top of mold to increase the magnetic field. Initial meniscus level should be controlled between the center and the top of coil to obtain the ideal soft contact effect. The alternating magnetic field could penetrate mold wall then impose on metal strand under the given conditions in this research. Magnetic field on vertical direction mainly acted on metal strand meniscus location. The magnetic flux density increased in the top half of mold, but decreased greatly in the down half of mold. The uniformity of magnetic flux density was good in circumferential direction and degenerate to boundary in radical direction. The magnetic field in the two-stage mold was more uniform than that in the slit mold, as was better for industry use.

ABSTRACT The effects of flow control device、casting flowrate of liquid steel and inclusion size on inclusion removal in continuous casting tundish were investigated by choosing emulsion drops simulated as inclusions in a water model. The results show that the efficiency of inclusion removal in tundish with weir and dams is relatively high due to the collision and aggregation of inclusions in high turbulence region and the improvement of flow field in tundish. Although the fluid flow has some change in pouring region with turbulence inhibitor in tundish, It has not much effect on the efficiency of inclusion removal. It seems to be difficult to improve the efficiency of inclusion removal only by optimizing the flow control devices in tundish with high casting flowrate of liquid steel.