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In this paper, several new powder packing methods are proposed, and the COMSOL software is used to simulate the temperature distribution under different conditions. The influence of powder packing on the growth of SiC single crystal by physical vapor transport (PVT) is studied. The results show that the heat flux of the top region of the powder is increased by trapezoid graphite and graphite ring, the radial temperature gradient of the powder is reduced, which contributes to the improve the powder utilization rate. By covering the surface of the powder with a layer of porous graphite filter, the recrystallization on the surface of the powder is inhibited, the defects of carbon inclusion and thermal stress in the SiC crystal are reduced, and the growth quality and growth rate of the SiC crystal are obviously improved. The simulation results were verified by experiment, and the results agrees well with experiment. [ABSTRACT FROM AUTHOR]

Co3O4 has been considered a promising anode material because of its high theoretical capacity (890 mAh/g) and remarkable energy density. Unfortunately, it suffers from low initial coulombic efficiency, rapid capacity fading, poor electronic conductivity, large volume changes, and aggregation during the lithium ion intercalation/deintercalation process. In this work, a series of Fe2+-doped Co3O4 nanostructured materials Co3(1-x)Fe3xO4 (x = 0, 0.01, 0.02 and 0.03) were produced by a simple chemical co-precipitation method. The Fe doping led to a slight increase of the lattice parameter, which is beneficial to the rapid diffusion of Li+ ion during the lithiation/delithiation process. Meanwhile, the Fe-doped Co3O4 sample exhibited an excellent rate capability of 886.47 mAh/g at 500 mA/g, and outstanding cyclic stability (1156.91 mAh/g for 50 cycles, with the capacity retention rate of 83.53% at the current density of 100 mA/g), demonstrating improved electrochemical performance, compared with that of pure Co3O4. The good electrochemical performance profited from the formation of oxygen vacancies by Fe doping, which provided more space for Li+ diffusion and improved the electronic conductivity of the anode material. This work provides a simple way to improve the comprehensive electrochemical performance of the transitional metal oxide Co3O4 anode electrodes for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

The microstructural evolution of Ti-45 at.%Al alloy during directional solidification was simulated by applying a solute diffusion controlled solidification model. The obtained results have shown that under high thermal gradients the stable primary spacing can be adjusted via branching or competitive growth. For dendritic structures formed under a high thermal gradient, the secondary dendrite arms are developed not very well in many cases due to the branching mechanism under a constrained dendritic growth condition. Furthermore, it has been observed that, with increasing pulling velocity, there exists a cell/dendrite transition region consisting of cells and dendrites, which varies with the thermal gradient in a contradicting way, i.e. increase of the thermal gradient leading to the decrease of the range of the transition region. The simulations agree reasonably well with experiment results.

The FDM numerical simulation software, ViewCast system, was employed to simulate the low pressure die casting (LPDC) of an aluminum wheel. By analyzing the mold-fi lling and solidifi cation stage of the LPDC process, the distribution of liquid fraction, temperature field and solidification pattern of castings were studied. The potential shrinkage defects were predicted to be formed at the rim/spoke junctions, which is in consistence with the X-ray detection result. The distribution pattern of the defects has also been studied. A solution towards reducing such defects has been presented. The cooling capacity of the mold was improved by installing water pipes both in the side mold and the top mold. Analysis on the shrinkage defects under forced cooling mode proved that adding the cooling system in the mold is an effective method for reduction of shrinkage defects.

Shrinkage defects can be formed easily at Critical location during low pressure die casting (LPDC) of aluminum alloy cylinder body. It has harmful effect on the products. Mold fi lling and solidifi cation process of a cylinder body was simulated by using of Z-CAST software. The casting method was improved based on the simulation results. In order to create effective feeding passage, the structure of casting was modifi ed by changing the location of strengthening ribs at the bottom, without causing any adverse effect on the part’s performance. Inserting copper billet at suitable location of the die is a valid way to create suitable solidifi cation sequence that is benefi cial to the feeding. Using these methods, the shrinkage defect was completely eliminated at the critical location.

The microstructure, precipitate type, precipitate distribution and tensile strength of a ZL205 alloy, before and after ageing treatment, have been studied by means of optical microscopy and transmission electron microscopy. The results showed that the as-cast microstructure of the alloy was made up of α-Al and eutectic phase distributed at the grain boundaries. During ageing treatment, the tensile strength increased at first and then reduced with time, and the highest ultimate tensile strength was found to be around 488.2 MPa.

NiCrAl/20%WC/MoS2 composite coatings with different MoS2 additions were prepared on the surface of 45 steel by laser cladding technology. The effects of MoS2 content on the microstructure, hardness and antifriction and wear resistance of the cladding layer were mainly studied. The results show that the content of lubricating phase has a certain influence on the hardness, anti-friction and wear resistance. With the increase of MoS2 content, the microstructure is gradually refined; the hardness gradually increases; the friction coefficient first decreases and then increases, and when the MoS2 content is 5%, the friction coefficient is at least 0.55; the wear volume first decreases and then increases, and the MoS2 addition amount is 5% When the wear volume is the smallest, the wear resistance is increased by 79% compared with the 45 steel substrate. Comprehensive analysis shows that the optimum addition amount of MoS2 is 5%. [ABSTRACT FROM AUTHOR]

Alloy composition design at the atomic scale is one of the key strategies for Ni-based single crystal superalloys (Ni-SCSs). In this article, the site preference of co-alloying elements Re-M (M: Cr, Mo, W or Re) in Ni3Al system and the strengthening effects of co-alloying elements on the shear deformation resistance of Ni3Al system are investigated using the first-principles method. It is found that the atom pairs of co-alloying elements prefer Al–Al site and the site preference of alloying elements is not affected by paired atoms. And co-alloying atom pairs occupying Ni–Ni site have a strong mutual interaction, which can be responsible for the formation of Re clusters and segregation of alloying elements. The ideal shear strength (ISS) of the quaternary Ni3Al system enhanced greatly by co-alloying elements is at least higher 11.9% than that of any Ni3Al system doped with single alloying elements, which indicates there are common effect among the co-alloying elements. The result of electronic structures shows that the strong interaction between the alloy atoms and their common the first nearest neighbors (FNN) Ni atoms is the common strengthening mechanism. The present article provides valuable guidelines for improving the mechanical strength of Ni-SCSs via alloy composition design. [ABSTRACT FROM AUTHOR]