Papers by Keyword: Oriented Growth

Abstract: The effects of SiC_p addition on the microstructure and mechanical properties of ZTA ceramics was investigated by microwave sintering. Partially stabilized zirconia（3Y-ZrO₂）nanopowder containing SiC_p was prepared by microwave pyrolysing precursor which was was achieved by co-precipitation method. The powders of alumina, yttria partially stabilized zirconia containing SiC_p were mixed to prepare ZTA ceramics green body by die pressing and cold isostatic pressing and subsequently sintered at the range of 1350°C-1550°C for 30min by microwave. XRD revealed that 3Y-ZrO₂/SiC powder contained more tetragonal phase than 3Y-ZrO₂ powder which was also confirmed by SEM and particle size distribution. The phenomenon was because of SiC_p forming the microwave heating spot that promoted pyrolysis progress when 3Y-ZrO₂/SiC powder was prepared by microwave heating. Microstructure showed that the grain of ZTA ceramics had directional growth by microwave sintering. SiC_p firstly absorbed microwave that made more uniform sintering of ZTA ceramics and caused local oriented growth of zirconia and alumina. Thus, the bending strength of ZTA ceramics was higher than ZTA without SiC_p. The ladder type heating mode of microwave sintering ZTA ceramics reduced relatively sintering time by 20min due to the addition of SiC_p.Introduction

Abstract: In many metallic materials the dominating recrystallization mechanism can be described by the oriented growth behavior. Phenomenological laws state that only these nuclei grow intensively which have a given misorientation with the deformed matrix. This description is frequently verified in f.c.c. metals and generally reported misorientations are between 30⁰ and 50⁰ rotations around the <111> axis. Basing on the above ideas the recrystallization model was formulated and applied to the study of recrystallization textures in rolled polycrystalline aluminium.

Abstract: Ba_0.6Sr_0.4TiO₃ (BST) thin films were fabricated by solgel technique on Pt/Ti/SiO₂/Si substrate without and with PbO seeding layer from precursor solutions with different concentrations. The crystal structure, surface morphology, dielectric properties and leakage current density of BST thin films are investigated as functions of the concentration of PbO precursor solution. Its found that the growth orientation of BST thin films with PbO seeding layer can be modulated through adjusting the concentration of PbO precursor solution. BST thin film with PbO seeding layer from 0.05 M precursor solution shows the highest dielectric constant and tunability, which may be attributed to the high crystallization and amplitude of the polarization in high (100) preferred orientated films. The leakage current density of BST films increases with the increasing concentration of PbO precursor solution and agrees well with the space-charge-limited current mechanism at room temperature.

Abstract: Due to its perovskite crystal structure and good conductivity, LaNiO₃ (LNO) can be used as the electrode for piezoelectric and ferroelectric films. With the development of the silicon-based integrated ferroelectrics, preparation of LNO electrode film with good conductivity is of great importance for high-performance ferroelectric films. In this paper, LNO sol was prepared using the nickel acetate and the lanthanum nitrate as starting materials, with the acrylic acid as stablizer. Through the sol-gel process, LNO films with certain crystal orientation were prepared on silicon substrate. The film microstructure and electrical properties were analyzed. Results indicate that through proper sol component and heat treatment process, (100)-oriented, mirror-like LNO films with low surface resistance of 50 Ω/ can be obtained, which can be used as the electrode for the ferroelectric films.

Abstract: The oriented-nucleation and oriented-growth for recrystallization (Rex) textures of electrodeposits, vapor deposits, and plastically deformed metallic materials have been discussed based on the strain-energy-release-maximization (SERM) model. When the Rex orientation predicted by the SERM model from major components of the deformation texture is the same as a minor component in the deformation texture that is calculated to be thermally stable by the SERM model, the calculated Rex orientation is sure to become the main component of the Rex texture. This implies that the oriented-nucleation and the oriented-growth affect the evolution of the Rex texture. For polycrystalline materials, the Rex orientation predicted by the SERM model is likely to be measured because heterogeneous nucleation can occur in grain boundaries even when shear bands are absent. In other words, the grain boundaries are unlikely to control the Rex texture and the oriented growth dominates the Rex texture.

Abstract: A possibility of a modification of the Jackson-Hunt theory of an oriented structure formation is analysed. A new model for the formation of a concentration field ahead of growing regular lamellae with respect to the solid / liquid interface shape is presented. A coordinate system applied in the model is attached to the solid / liquid interface to be advancing in the z - direction, identically with interface moving at a constant velocity, v . The solution to a diffusion equation is given for the improved formulation of the boundary conditions. The boundary conditions are related to the interplay between the diffusion required for phase separation and the formation of the interphase between both lamellae. The boundary conditions are formulated to establish the stability of lamellar structure formation under steady-state conditions. It is assumed that stable growth of the lamellae is ensured by the separation of concentration fields within a boundary layer ahead of the solid / liquid interfaces of both the α and β " phases. Coupled lamellar growth with the presence of a leading phase protrusion is defined. The general mass balance is analysed for a solute concentration in the liquid, taking into account a planar solid / liquid interface. A local mass balance is also ensured but it requires envisaging a protrusion of the minor eutectic phase. The existence of a lead distance is confirmed experimentally for the (Pb)-(Cd) eutectic system. The difference in undercooling is also considered as a phenomenon associated with the separation of concentration fields and the existence of a protrusion to relax the assumption of an isothermal interface (ideally coupled growth) given by the Hunt and Jackson theory.

Abstract: The paper presented the texture evolution during primary recrystallization and following grain growth in the heavily cold-rolled Ni3Al single crystals. It turned out that the texture evolution occurred in the two stages. First, primary recrystallization caused the drastic change of the as-rolled texture. Then, as grain growth proceeded, the texture returned to the same one as the as-rolled textures. This texture return can be designated as Texture memory effect. The mechanism of the texture memory effect was discussed based on the analysis of the orientation relationship between the as-rolled and the primary recrystallization textures.