Abstract: In this study, the temperature field distribution of 22CrMoH billet is first obtained by simulating continuous casting process using moving boundary method. On the basis of the above data, the microstructure of 22CrMoH gear steels billet was simulated based on CAFÉ (Cellular Automaton – Finite Element Analysis) method, together with the effects of alloying elements such as Cr, Mo, Si, Mn on the microstructure of this billet. The simulated result agrees reasonably well with that of the actual product. And it suggested that under the reasonable extend of current steel grade, the increased amount of Si and Mn can steadily widen the proportion of equiaxed grains, lead to the increase in equiaxed grain amount, hence the decrease in equiaxed grain average radius; The increase in Mo content is able to enhance the nucleation amount; Proper decrease in Cr content favors the increase in proportion of equiaxed grains, but little effects on grain’s amount and radius. Further, the composition of alloy elements under the specified scope of 22CrMoH grade was optimized and the simulated results showed that the microstructure has vastly improved, as the proportion of equiaxed grain rose nearly doubled, the grains amount has increased by 19.96%, and average radius has decreased by 9.20%.
Abstract: AZ31 magnesium alloy profiles were prepared by continuous rheo-extrusion, and effects of annealing temperature and time on recrystallization of AZ31 magnesium alloy were investigated. The results reveal that when the profile is annealed in the temperature range from 200°C to 300°C, the moving velocity of grain interface with different dislocation densities on both sides increases with increasing annealing temperature, which is favorable to the formation of crystallized nucleus in the region in which interface sweeps over. As a result, the time required by the accomplishment of recrystallization becomes short. After recrystallization finishes, continuous temperature rise or prolonged holding time result in grain growth. When the profile is annealed at elevated temperature, with the prolongation of holding time, the grain growth rate accelerates obviously, and hence recrystallized microstructure becomes coarse. When the profile is annealed at lower temperature, the grain growth rate becomes small, and the time required by the accomplishment of recrystallization is long, but recrystallized microstructure is fine and homogeneous. When the profile is annealed at 250°C for 4h, average recrystallized grain size is 15μm.
Abstract: Mixed ionic-electronic conducting BaCo0.7Fe0.2Nb0.1O3-δ perovskite is a newly developed promising ceramic membrane material. In this work, the stability and permeability of BaCo0.7Fe0.2Nb0.1O3-δ regarding the special requirements for CCS application are investigated. CO2 would deteriorate the membrane performance by decreasing gradient of oxygen vacancy across bulk and surface carbonatation.
Abstract: Membrane surface modification is the important method to decrease membrane fouling. The hydrophilic modification of ceramic membrane with nano-sized inorganic coating is prepared by the wet chemical methods. The thin nano coating is not a separating top layer but distributes uniformly on the surface of the membrane pore wall. The coating does not change the structure of the membrane pores. Therefore, water flows on not the pore wall but the nano coating surface. The results show that the water flux of the modified membrane is higher than that of the unmodified membrane despite that the mean pore size of the modified membrane decreases. The “boundary slip” is used to explain this special phenomenon. What generates the slippage? The slippage is relative with the molecular layer adhered tightly on the hydrophilic pore wall, the roughness and the surface charge of the nano coating, the interaction between the ions in water and the nano coating, et al.
Abstract: A facile homogenous precipitation method has been developed for the synthesis of multifunctional, luminescent, and magnetic nanocomposites with Fe2O3 nanospheres as the core and europium-doped yttrium oxide (Y2O3:Eu3+) as the shell. The nanocomposites show both ferromagnetic behavior and excellent fluorescence properties with high emission intensity. The luminescent and magnetic properties of the multifunctional nanocomposites can be easily tuned by changing the synthesis conditions, which may find potential applications in biological fields.
Abstract: Fe-Ni-Cr alloy powders with CeO2 were flame sprayed and fused on the surface of 1045 carbon steel substrate. The effect of CeO2 on microstructure and tribological behavior of coatings were studied experimentally by means of scanning electron microscopy (SEM), field emission gun scanning electron microscopy (FEGSEM), energy dispersive spectroscopy (EDS) and wear tests. The results show that an adhered oxide debris layer was formed on the worn surface in friction which contributed to decreased wear. Wear rate of the material increased with the load, but dramatically decreased at first and then slightly decreased the sliding speed. The friction coefficient of the material decreased slightly with the load, but increased with sliding speed at first, and then tended to be a constant value. Wear mechanism of the coatings was oxidation wear and a large amount of counterpart material was transferred to the coatings, the RE oxide in the debris layer contributes to the improvement in wear resistance.
Abstract: Photocatalytic degradation of methyl orange in water was examined using Co-doped TiO2 nanoparticles. These photocatalysts were synthesized by a sol–gel method from titanium tetra-isopropoxide with different concentrations of Co(III) dopant and calcination temperature at 600°C. The samples were characterized by XRD, DRS, TEM analysis. The XRD results showed that the anatase-to-rutile phase transformation was greatly inhibited by Co ion doping. The increase of Co doping enhanced “red-shift” in the UV-vis absorption spectra. The TEM images confirmed the dopants suppressed the growth of TiO2 grains. The photocatalytic activity of the nanoparticles under UV light was investigated by measuring the photodegradation of methyl orange solutions. Parameters affecting photocatalytic process such as the dosage of catalyst, dopant and methyl orange concentrations were investigated. The degradation process was optimized using a Co concentration of 1.0 mol%, 30mg Co-doped TiO2 and MO concentration of 10mg/L.
Abstract: High chromium cast iron alloys are widely used to produce wear resistant components. However, formation of the large carbides restricts their applied range for the components by traditional solidification techniques. The gas atomization is an effective approach to refine their structures, improve their properties and extend their application field. Based on the study of structure evolution of atomized powders of Fe-25Cr-3.9C alloy, this paper investigated the structure evolution of the atomized powders of Fe-25Cr-3.9C alloy with addition of Ni and B elements. It is found that addition of Ni and B elements make more primary lath-shaped phase be formed. As particle size decrease, width of the primary lath-shaped phase gradually decreases, and the structures are all composed of lath-shaped phase in the small powders with diameter less than 38mm. At last, a relative study between two alloys was made, and the structure formation of atomized powders was discussed.
Abstract: Annealing treatments at 200°C, 250 °C, 300°C, and 350°C were conducted on a twin-roll casted AZ31 sheet with an initial average grain size of 10.11 mm. Microstructure and mechanical behaviors were studied by optical microscope observation and tensile mechanical test. Expermeintal results show that grain size experienced three stage evolution during 180 min annealing at each temperature: recrystallization refinement, stabilization under dynamic balance of recrystallization and grain growth, and grain growth. The minimum average grain size of 5.96 μm was achieved after 120 min annealing at 200°C. The refined grain structure causes a decrease of ultimate tensile strength and an increase of elongation, and facilitates superplastic deformation of the material.