Anthony D. Rollett

Operational texture analysis

Abstract A comprehensive overview is presented of the elements that enter quantitative techniques of texture measurement, analysis and representations. There are many potential errors to be corrected and many choices to be made in all these stages, and we present those that we consider most appropriate. They have been implemented in a software package that is available publicly. A number of novel techniques are used including, for example, in the representation of measured textures, both for quantitative visual inspection and for use in the prediction of anisotropic properties. The symmetry of the test sample is allowed to be general, and that of the crystal structure may be as low as trigonal.

Simulation and theory of abnormal grain growth—anisotropic grain boundary energies and mobilities

Abnormal grain growth has been studied by means of a computer-based Monte Carlo model. This model has previously been shown to reproduce many of the essential features of normal grain growth. The simulations presented in this work are based on a modified model in which two distinct types of grains are present. These two grain types might correspond to two components of different crystallographic orientation, for example. This results in three classes of grain boundaries: (a) between unlike types, (b) between grains of the tirst type and (c) between grains of the second type, to which different grain boundary energies or different mobilities can be assigned. Most simulations started with a single grain of the first type embedded in a matrix of grains of the second type. Anisotropic grain boundary energies were modeled by assigning a higher energy to boundaries between like type than to boundaries between grains of unlike type. For this case, abnormal grain growth only occurred for an energy ratio greater than 2 and then wetting of the matrix by the abnormal grain occurred. Anisotropic grain boundary mobilities were modeled by assigning a lower mobility to boundaries between grains of like type than to boundaries between unlike type. For this case the extent of abnormal grain growth varied with the ratio of mobilities and it is tentatively concluded that there is a limiting ratio of size of the abnormal grain relative to the matrix, A simple treatment of anisotropic grain boundary mobility was developed by modifying Hillerts grain growth model (Acta meralf. 13,227 (1965)I. This theoretical treatment also produced a limiting ratio of relative size that is a simple function of the mobility ratio. RhsumP-La croissance anormale des grains a ete u (b) entre grains du premier type; (c) entre grains due second type, auxquels peuvent @tre assignees differentes energies intergranulaires ou differentes mobilitts. La plupart des simulations concernent un seul grain du premier type entoure par une matrice de grains du second type. On a tenu compte des energies intergranulaires anisotropes en assignment aux joints separant des grains du mm entsprechend konnen diese Korngrenzarten unterschiedliche Energien und Beweglichkeiten aufweisen. Die meisten der Simulationen begannen mit einem einzigen Kom des ersten Typs, welches in einer Matrix von Kornem des zweiten Typs eingebettet war. Anisotrope Komgrenzenergien wurden im Model1 beschrieben, indem den Komgrenzen zwischen gleichen Komem eine hohere Energie als zwischen ungleichen Kiimern zugeschrieben wurde. In diesem Fall ergab sich anormales Kornwachstum nur, wenn das Verhaltnis der Energien griil3er als 2 war und dann das anormale Kom die Matrix benetzte. Anisotrope Korngrenzbeweglichkeiten wurden im Model1 beschrieben, indem Komgrenzen zwischen Kdrnem des gleichen Typs mit einer geringeren Beweglichkeit als zwischen ungleichen Kiimern versehen wurden. In diesem Fall hing der Grad des anomalen Wachstums von dem Verhaltnis der Beweglichkeiten ab; daraus kann gefolgert werden, daB es eine Grenze

The Distribution of Internal Interfaces in Polycrystals

Recent advances both in experimental instrumentation and computing power have made it possible to interrogate the distribution of internal interfaces in polycrystals and the three dimensional structure of the grain boundary network with an unprecedented level of detail. The purpose of this paper is to review techniques that can be used to study the mesoscopic crystallographic structure of grain boundary networks and to summarize current findings. Recent studies have shown that grain surfaces within dense polycrystals favor the same low energy planes that are found on equilibrium crystal shapes and growth forms of crystals in contact with another phase. In the materials for which comprehensive data exists, the distribution of grain boundaries is inversely correlated to the sum of the energies of the surfaces of the grains on either side of the boundary.

Epitaxial CeO2 films as buffer layers for high-temperature superconducting thin films

We have prepared epitaxial (100)CeO2 thin films on LaAlO3, sapphire, and yttria‐stabilized zirconia using pulsed laser deposition. It is demonstrated in this letter that the CeO2 films are chemically and structurally compatible to the high‐temperature superconductor YBa2Cu3O7−δ (YBCO). Epitaxial YBCO films on CeO2/LaAlO3 had a zero resistance temperature and critical current density in a zero field of 90 K and 5.9×106 A/cm2 at 75 K, respectively. Furthermore, epitaxial multilayers of CeO2/YBCO were prepared. This work demonstrated that CeO2 is an excellent buffer layer material for the high‐temperature superconductors.

Viewpoint: experimental recovery of geometrically necessary dislocation density in polycrystals

Abstract Application of electron backscattering diffraction methods to recover estimates of the geometrically necessary dislocation density is described. The limitations of the method arising from the opacity of crystalline materials and the spatial and angular resolution limits are discussed.

Computer simulation of recrystallization—II. Heterogeneous nucleation and growth

Abstract A two-dimensional Monte Carlo computer simulation technique, in which a continuum system is modeled employing a discrete lattice, has been applied to the problem of primary recrystallization. The stored energy is varied between levels allowing homogeneous nucleation and nucleation only on pre-existing grain-boundaries and grain-boundary vertices. The attempted nucleation rate is chosen as either constant rate or site saturated. Temporal evolution of the simulated microstructures are analyzed to provide the time dependence of the recrystallized volume fraction. The recrystallized volume fraction shows sigmoidal variations with time. The long time data are approximately fit by the Johnson-Mehl-Avrami-Kolmogorov equation with the expected exponents for the operative nucleation mechanism, however significant deviations are observed at early times. The recrystallized microstructures are analyzed to give the grain size distribution function and the topological distribution function (number of domain edges). Compared to grain growth microstructures, where the grain size is proportional to the number of edges, the recrystallized microstructure shows significant deviation from this relation.

Design of Radiation Tolerant Materials Via Interface Engineering

A novel interface engineering strategy is proposed to simultaneously achieve superior irradiation tolerance, high strength, and high thermal stability in bulk nanolayered composites of a model face-centered-cubic (Cu)/body-centered-cubic (Nb) system. By synthesizing bulk nanolayered Cu-Nb composites containing interfaces with controlled sink efficiencies, a novel material is designed in which nearly all irradiation-induced defects are annihilated.

On abnormal subgrain growth and the origin of recrystallization nuclei

Abnormal subgrain growth has been proposed as the nucleation mechanism for recrystallization. To test this hypothesis, Monte Carlo Potts model simulations of subgrain growth were performed on single-phase, strain-free subgrain structures with experimentally validated microstructure, texture, boundary character, and boundary properties. Results indicate that abnormal growth events emerge spontaneously during evolution in such systems, and abnormal subgrains behave as predicted by mean field theory. An analysis predicts the frequency of abnormal growth events as a function of local neighborhood and the boundary misorientation distribution. A recrystallization model is derived based on the abnormal subgrain growth analysis. Using data for aluminum subgrain structures, the model predicts reasonable recrystallized grain sizes as a function of von Mises strain. The extension of these results to abnormal grain growth is discussed.

A hybrid model for mesoscopic simulation of recrystallization

A brief summary of simulation techniques for recrystallization is given. The limitations of the Potts model and the cellular automaton model as used in their standard forms for grain growth and recrystallization are noted. A new approach based on a hybrid of the Potts model (MC) and the cellular automaton (CA) model is proposed in order to obtain the desired limiting behavior for both curvature-driven and stored energy-driven grain boundary migration.

Overview of modeling and simulation of recrystallization

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