Grain Growth Morphology Research Articles

Influence of α-alumina seed on the morphology of grain growth in alumina ceramics from Bayer aluminum hydroxide

The preparation of alumina ceramics started with commercial aluminum hydroxide from the Bayer process. Abrasives were introduced to the starting materials by the wet grinding of high-purity alumina milling balls. Abrasives played the role of seeds, lowering the transformation temperature of aluminum hydroxide to alumina. The phase transformation from aluminum hydroxide to α-Al 2O 3 was completed at 1100 °C in 2 h with a certain amount of seeds added. Seed also changed the sintering behavior and microstructure of calcined powders. In this paper, the relationship between seed concentrations and grain morphology was investigated. The alumina grain morphology showed a trend of change from equiaxed grain to hexagonal platelets, and finally to elongated grains with increase of the seed concentration.

Generalized phase-field model for computer simulation of grain growth in anisotropic systems

We study the dynamics and morphology of grain growth with anisotropic energy and mobility of grain boundaries using a generalized phase field model. In contrast to previous studies, both inclination and misorientation of the boundaries are considered. The model is first validated against exact analytical solutions for the classical problem of an island grain embedded in an infinite matrix. It is found that grain boundary energy anisotropy has a much stronger effect on grain shape than that of mobility anisotropy. In a polycrystalline system with mobility anisotropy, we find that the system evolves in a non-self-similar manner and grain shape anisotropy develops. However, the average area of the grains grows linearly with time, as in an isotropic system.

Recrystallization and Related Phenomena. Monte Carlo Simulation of Grain Growth in Three-dimensions.

The temporal evolution and morphology of grain growth in three dimensions were simulated by Monte Carlo method. In order to prevent impingement of grains of like orientation, new algorithm was adopted. The anisotropy of the grain boundary energy is incorporated into the model. Compared with the case in which no anisotropy of boundary energy is assumed, the suppression of grain growth was observed at the initial stage of growth in the grain structure with anisotropic grain boundary energy. However, the growth rate is higher at the later stage. The grain size and the face number distributions become broad. To evaluate the profile of the grain size distribution, a parameter called microstructural entropy, S, is defined. It was shown that the characteristics of size distribution profile may be represented by the value S. The average size of n-faced grain is proportional to the grain face number, n. The effect of the anisotropy of grain boundary energy on the n-dependence of the average grain size is not evident. The nearest neighbour face number correlation similar to the Aboav-Weaire relation in two dimension is observed in both grain structures with isotropic grain boundary energy and anisotropic grain boundary energy.

Morphology of grain growth in response to diffusion induced elastic stresses: cubic systems

In diffusion-induced recrystallization (DIR), diffusion of a misfitting solute produces coherency strains in a solid and can lead to nucleation of new grains. The local interface velocity of the newly nucleated grains depends only on the magnitude of the reduction in the elastic energy density of the coherently stressed solid ahead of the migrating grain boundary, which in turn depends only on the local interface normal of the shrinking grain. Real-space calculations of the orientation-dependent elastic energy density are outlined in general and specific results are given for cubic systems. The method of characteristics described recently by Cahn, Taylor and Handwerker is employed to obtain predictions of the evolution in grain shape with time and the range of possible limiting growth shapes in terms of the edges and corners which develop on any growing grain. When the growing grain is free of elastic strains, the possible morphologies depend on only two parameters: the elastic anisotropy α (≡2( s 11 − s 12)/ S 44), and normalized linear compressibility β( s 11 + 2 s 12)/ S 44). When the elastic anisotrophy α > 1, the morphology tends to be cuboidal, but the exact shape is found to depend on the value of the linear compressibility. For α < 1, the morphology tends to be octahedral.

Nucleation and Growth kinetics of Cu2O During Reduction of CuO Thin Films

AbstractThe combination of 16O(α, α)16O oxygen resonance measurement and transmission electron microscopy (TEM) provides an unique and effective method to study the kinetics of nucleation and growth of Cu2O phase during reduction. In situ TEM observation showed that isolated and large Cu2O grains emerge from the small CuO grain matrix and the growth of Cu2O grains is linear with time. We propose that the discontinuous morphology of grain growth of Cu2O is due to the migration of the Cu2O-CuO phase boundary induced by oxygen out-diffusion along the moving phase boundary. Based on the classical analysis of phase transformation by Johnson, Mehl and Avrami, the activation enthalpy of nucleation of Cu2O phase in the CuO matrix has been deduced as ΔEn=2.3 eV. The specific interfacial energy between CuO and Cu2O phases has been estimated as 0.5 eV/atom.

Oxygen-diffusion-induced phase boundary migration in copper oxide thin films.

The transition of copper oxide thin films from CuO to ${\mathrm{Cu}}_{2}$O during vacuum annealing has been studied by transmission electron microscopy and Rutherford backscattering spectroscopy. Dark field images show that isolated and large ${\mathrm{Cu}}_{2}$O grains emerge from the small CuO grain matrix. The abrupt change in oxygen concentration across the phase boundary between CuO and ${\mathrm{Cu}}_{2}$O in the reaction is different from the continuous change of $\ensuremath{\delta}$ in oxidation and reduction of the superconducting $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ oxide. The growth of ${\mathrm{Cu}}_{2}$O grains is linear with time and has an activation energy of 1.1 eV. We propose that the discontinuous morphology of grain growth of ${\mathrm{Cu}}_{2}$O is due to the migration of the ${\mathrm{Cu}}_{2}$O-CuO phase boundary induced by oxygen out-diffusion along the moving phase boundary.

Effect of a Liquid Phase on the Morphology of Grain Growth in Alumina

In this investigation we have studied how the presence of a liquid phase affects the grain morphology and grain growth kinetics in Al2O3 at 1800°C using the growth of both matrix grains and large spherical single‐crystal seeds growing into the matrix. The growth rates of the matrix grains were found to decrease in the following order: undoped Al2O3, AI2O3 with anorthite, AI2O3 with anorthite and MgO, and Al2O3 with MgO. Except for the samples doped with MgO alone, the matrix grains were faceted and appeared tabular in polished sections. In samples containing anorthite both with and without MgO, the single‐crystal seeds exhibit basal facets with continuous liquid films and slow growth in the 〈0001〉 relative to all other crystallographic directions. When only MgO is added, the growth of the single‐crystal seeds was not isotropic; however, no faceting was observed. We discuss how anisotropic growth rates caused by the anorthite additions can stimulate discontinuous grain growth in Al2O3.