Papers by Keyword: Grain Morphology

Abstract: The sample with nominal composition of Bi_1.6Pb_0.4Sr₂Ca_2-xEu_xCu₃O_y where x = 0.000, 0.0025, 0.020, 0.050 and 0.100 were synthesized through solid state reaction method. The effect of Eu₂O₃ nanoparticles doping on the superconducting and structural properties were studied by means of critical temperature, T_C, critical current density, J_C, X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The amount of 2223 phase gradually decreased with the increment of Eu concentration which indicates that Eu nanoparticles substitution at Ca site favours the growth of 2212 phases. The sample with higher porosity was found to be decreased in critical temperature, T_C as well as critical current density, J_C due to the lack of effective surface area for current flowing. The best superconducting properties were observed at x = 0.0025 substitutes into Ca site for Bi (Pb)-2223 host sample.

Abstract: The wettability between silicon carbide and aluminum is poor, silicon carbide is difficult to fuse or the distribution of silicon carbide is not uniform in the ingot when the SiCp / 7075 composite is prepared by melt casting.The surface modification of SiCp by nickel plating can significantly reduce the wetting angle of SiC/Al and improve the distribution uniformity of silicon carbide in SiCp / 7075. In this thesis, the thermal compression process 6.5% SiCp / 7075 reinforced by nickel-plated modified silicon carbide is simulated by DEFOEM-3D software.The influence of the shape and particle size of nickel-plated modified silicon carbide on its compressive damage has been highlighted, and the deformation characteristics of the SiC/Ni/Al interface layer in the thermal compression process have been discussed. The numerical simulation results show that the 6.5% SiCp / 7075 reinforced by spherical nickel-plated modified silicon carbide particles with a particle size of 15 μm has the smallest compression damage value of 0.0426, at this point the compression temperature is 400°C, the compression ratio is 15, and the compression rate is 0.03s^-1. the hot compression test of 6.5% SiCp / 7075 reinforced by spherical nickel-plated modified silicon carbide particles with a particle size of 15 μm was performed by using the same compression parameters as the numerical simulation. After hot pressing, the sample had a smooth surface with few obvious cracks, which was consistent with the numerical simulation results. Key words: nickel-plating modification; silicon carbide particles; compressive damage; grain size; grain morphology

Abstract: It is well known that nanocrystalline materials have enhanced diffusion properties due to their high grain boundary density which act as fast diffusion channels compared to the lattice. In this paper, we aim at simulating the nitriding process of a pure iron nanostructured by NanoPeening® process. We use a simple diffusional approach taking into account the grain size and the grain morphology resulting from the NanoPeening® treatment. EBSD measurements are carried out to extract morphological parameters which are used in the homogenization method to extract the effective diffusivity distribution. Then a 1D diffusion simulation is performed with this distribution and shows that the grain morphology resulting from the NanoPeening® treatment does not deteriorate the diffusion properties of the material but in fact, improves the nitrogen penetration depth and the diffusion kinetics in addition to the effect of the grain size reduction.

Abstract: The paper investigates by numerical modeling the effects of crystallographic texture and grain shape on the shape of the yield surface of aluminum sheet material at small strains. Different representative volume elements (RVEs) of the material are considered. Plane stress state is assumed in the sheet. A rate-dependent model of crystal plasticity (CP) is used in combination with either the full-constraint (FC) Taylor model or the finite element method (FEM) to compute the volume averaged stress of the material. The effect of different crystallographic textures observed in aluminum alloys on the shape of the yield surface is firstly investigated. An analytical yield function is used to generate yield surfaces for the different crystallographic textures. The deviation between the stress states at yielding computed by FC-Taylor model and the analytical yield surface is used to evaluate the capability of the yield function to fit the anisotropic yield surfaces representing different strong crystallographic textures. Two different shapes of the grains are introduced in the RVEs of CP-FEM in order to study the effect of the grain morphology. Small effects of grain shape are found at small strain compared with the marked influence of crystallographic texture.

Abstract: A series of MnO-doped ZnO with different grain sizes and grain morphologies were prepared by sintering the samples at different temperatures for different holding times. The grain size distribution for each sample was determined. It was found that, although the grain size increases and the grain morphology varies with the sintering temperature and/or the holding time, the normalized grain size distribution keeps invariable.

Abstract: Using modifications to the Rappaz-Drezet-Gremaud hot tearing model, and using empirical equations developed for grain size and dendrite arm spacing (DAS) on the addition of grain refiner for a range of cooling rates, the effect of grain refinement and cooling rate on hot tearing susceptibility has been analysed. It was found that grain refinement decreased the grain size and made the grain morphology more globular. Therefore refining the grain size of an equiaxed dendritic grain decreased the hot tearing susceptibility. However, when the alloy was grain refined such that globular grain morphologies where obtained, further grain refinement increased the hot tearing susceptibility. Increasing the cooling decreased the grain size and made the grain morphology more dendritic and therefore increased the likelihood of hot tearing. The effect was particularly strong for equiaxed dendritic grain morphologies; hence grain refinement is increasingly important at high cooling rates to obtain more globular grain morphologies to reduce the hot tearing susceptibility.

Abstract: Pure nickel powder was low pressure plasma sprayed onto a steel substrate held at different temperatures during spraying. The as-sprayed coatings consist of columnar grains whose axes are nearly perpendicular to the lamellae composing the coatings. As the coating temperature becomes higher, the length of the columnar grains increases and is longer than the thickness of the lamellae, indicating the growth of the grains across the lamellar interfaces during spraying. On the other hand, the coatings that were heat treated after spraying consist of coarse equiaxed grains. The coatings that experienced high temperatures during spraying or the heat treated coatings have large porosity and contain large globular pores. The hardness, apparent density and the tensile strength of the coating itself were the highest for the coating prepared at a low temperature and became low on heat treatment. The thermal conductivity in the direction perpendicular to the coating was the largest for the coating that consisted of long columnar grains.