Advanced Materials Research Vols. 690-693

Abstract: The effect of annealing temperature（300-600°C）on the microstructure and transformation temperature of NiTiNb shape memory alloy rods deformed with equal channel angular pressing（ECAP） method was analyzed. The results show that the hard brittle phase （Ti,Nb）₂Ni was decreased after ECAP. With the rising of annealing temperature, the number of β-Nb phase increase while eutectic declines. The DSC analysis shows that the martensite and reverse transformation temperature increase with annealing temperature. After annealing with 500°C, the martensite/austenite transformation starting temperatures rise to -64.6°C and -30.1°C, respectively.

Abstract: The flow response and dynamic recrystallization of near-α Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd titanium alloy has been studied using isothermal hot compressive tests at strain rate of 0.01-10s^-1 in near β transus. The true stress-true strain curves hot-compressed in near-β region show a steady-state regime. The deformation is governed essentially by the β behavior. At strain rate of 10 s^-1, the alloy exhibited plastic flow instabilities. Dynamic recrystallization can take place for the 0.06%C alloy.

Abstract: The liquid structure of Ni₂Sb₉₈ eutectic alloy is studied with the method of X-ray diffraction and measurements of viscosity in this paper. Covalent bonding structures, which are characterized by the shoulder on the high- Q side of the first peak of structure factors, are observed over the full measuring temperature range. And the split of second peak of the pair correlation function suggests that the chemical short-range order structure exits in the melt. Correspondingly, variation of the viscosity obeys the Arrhenius law except the abrupt point near 1025K and the electrical resistivity changes abnormally at about 1020K. In addition, the coordination numbers prove that the A7-like structure is almost destroyed in liquid Ni₂Sb₉₈ alloy. This research is aim to provide new insight into the structure evolution of liquid alloys during the cooling process.

Abstract: The relationship among stress, cavities and twinning in the room-temperature bending process of hot-rolled AZ31 Mg alloy sheet was researched. It can be seen that the mount of twins which was tightly affected by stress value increases with the distance to press point. Otherwise, the cavities and twinning which seem totally independent, in fact affect with each other. Some cavities were hindered by twins and can not further grow up. Then, the relationship between slip and twinning was also roughly discussed. The dislocation lines in twins can be thought to release the stress focus and were beneficial for deformation.

Abstract: To study spacecraft shield structure against hypervelocity impact of space debris and its protective performances, 25mm ballistic gun launching 12.7mm cylindrical debris is selected against Aluminum foam composite structure at high speed. Based on the experimental results and analyze the effects of Aluminum foam protective structure with different combinations, the result is that protective effects with Aluminum foam in front of glass fiber is better.

Abstract: A novel process of solid-oxide-oxygen-ion conducting membrane (SOM) technique has been investigated to produce Ta metal directly from Ta₂O₅ in molten CaCl₂. The sintered porous Ta₂O₅ pellet was employed as the cathode while liquid copper, saturated with graphite powder and encased in a one-end-closed yttria-stabilized-zirconia (YSZ) tube, acted as the anode. The particle sizes and porosity of the cathode pellets are important factors that have significant impact on the electrolysis process. The optimal experimental conditions is pellet sintering and electrolytic temperature 1100°C, cell voltage 3.5V, electrolysis time 2h.

Abstract: Tantalum metal was prepared by Solid Oxygen-ion Conducting Membrane (SOM) technology from Ta₂O₅ directly in molten CaCl₂. Through reaction mechanism of the metal-oxide-electrolyte three-phase interline (3PIs), the influence of pellets microstructure on the electrolysis process and products morphology were discussed. The results demonstrate that forming pressure, particle size and porosity of cathode pellets are significant factors for three-phase interline during electrolysis process. It was found that the big porosity and small particle can enhance the deoxidization rate, Contrarily, the compact out-layer of tantalum metal was formed. While the Ta2O5 pellet was pressed by 4MPa and sintered at 1150°C for 2 h has rational porosity and particle, the electrochemical reduction can be achieved via two steps: Ta₂O₅Ta₂O_5-xTa.

Abstract: The present explains sintering characters of the Al₂O₃-86 homogenized bauxite under wet processes homogenization, which includes classified bauxite mine, wet grinding, vacuum extrusion, sintering in tunnel kiln,etc. DSC and TG reveal an evident peak of absorption heat at 531°C, resulting from the dehydroxylation of bauxite. Green samples held at 550°C*6hrs were heated up to different temperatures, and the properties of weight loss, linear change, bulk density and apparent porosity were measured. The data show that liquid-phase emerge and sintering process goes slowly above 1100°C. At 1500°C, large amounts of liquid-phase form, making liquid-phase sintering have a positive effect. The analysis of XRD and SEM indicate that, corundum grains develop more inadequate and most of the corundums interlace in a compact way, which can separate the widespread liquid phase and improve the sintering capability of homogenized bauxite.

Abstract: As a new effort, combined reactive sintering with hot pressing technique, the Ti-22Al-25Nb alloy was successful prepared with element mixed powders. Meanwhile, the reactive sintering was divided into two temperature ranges, which were at 873 K and 1373 K, respectively. The starting sintering kept 1h at 873K, and then the temperature was increased to 1373K, keeping 2h. The orthorhombic (Ti2AlNb) phase was observed in this sintered alloy. Moreover, the homogenization treat was conducted at 1473 K for 2h after the final sintering was accomplished, and the fraction of the orthorhombic phase increased significantly. The microstructures and the phases were analyzed. And the generation mechanism of the orthorhombic phase was also analyzed.