Different full field models exist for the simulation of anisotropic grain growth in polycrystalline structures. In the present work, two full field methods i.e. level set (LS) and multi-phase-field (MPF) methods are implemented into finite element (FE) formulations. The model formulation and simulation results are compared on FE unstructured mesh for the two methods. Relationships between the parameters in both models representing same grain boundary properties are derived. Using equivalent model parameters, both methods can provide similar numerical accuracy in the case of different theoretical test of 2D anisotropic grain growth. In addition, two 2D large scale grain growth simulations are performed with respectively isotropic and anisotropic grain boundary energies by level set method to illustrate the performance of this full field approach. (C) 2015 Elsevier B.V. All rights reserved.

The effects of prior stored energy level, annealing temperature, heating velocity, and initial grain size on annealing twin development during static recrystallization of commercially pure nickel (99.999 \%) are investigated. The twin content (measured as the twin boundary density or as the number of twins per grain) at the end of recrystallization is shown to be primarily influenced by the prior stored energy level and by the initial grain size, but the effects of heating rate and the annealing temperature are negligible. Taken together, the results are consistent with a new proposition that roughness of the recrystallization front promotes the formation of annealing twins during recrystallization.

The determination of grain boundary normals is an integral part of the characterization of grain boundaries in polycrystalline materials. These normal vectors are difficult to quantify due to the discretized nature of available microstructure characterization techniques. The most common method to determine grain boundary normals is by generating a surface mesh from an image of the microstructure, but this process can be slow, and is subject to smoothing issues. A new technique is proposed, utilizing first order Cartesian moments of binary indicator functions, to determine grain boundary normals directly from a voxelized microstructure image. To validate the accuracy of this technique, the surface normals obtained by the proposed method are compared to those generated by a surface meshing algorithm. Specifically, the local divergence between the surface normals obtained by different variants of the proposed technique and those generated from a surface mesh of a synthetic microstructure constructed using a marching cubes algorithm followed by Laplacian smoothing is quantified. Next, surface normals obtained with the proposed method from a measured 3D microstructure image of a Ni polycrystal are used to generate grain boundary character distributions (GBCD) for Sigma 3 and Sigma 9 boundaries, and compared to the GBCD generated using a surface mesh obtained from the same image. The results show that the proposed technique is an efficient and accurate method to determine voxelized fields of grain boundary normals.

Abstract Three-dimensional near-field high-energy X-ray diffraction microscopy has been used to observe the formation of new twinned grains in high purity Ni during annealing at 800 $\,^\circ$C. In the fully recrystallized microstructure annealed at 800 $\,^\circ$C, twinned grains form along triple lines. Both the grain boundary character and the grain boundary dihedral angles were measured before and after the twin formed. These measurements make it possible to show that although each new twinned grain increases the total grain boundary area, it reduces the total grain boundary energy.

A fast Fourier transform (FFT) based spectral algorithm is used to compute the full field mechanical response of polycrystalline microstructures. The field distributions in a specific region are used to determine the sensitivity of the method to the number of surrounding grains through quantification of the divergence of the field values from the largest simulation domain, as successively smaller surrounding volumes are included in the simulation. The analysis considers a mapped 3D structure where the location of interest is taken to be a particular pair of surface grains that enclose a small fatigue crack, and synthetically created statistically representative microstructures to further investigate the effect of anisotropy, loading condition, loading direction, and texture. The synthetic structures are generated via DREAM3D and the measured material is a cyclically loaded, Ni-based, low solvus high refractory (LSHR) superalloy that was characterized via 3D high energy x-ray diffraction microscopy (HEDM). Point-wise comparison of distributions in the grain pairs shows that, in order to obtain a Pearson correlation coefficient larger than 99%, the domain must extend to at least the third nearest neighbor. For an elastic FFT calculation, the stress—strain distributions are not sensitive to the shape of the domain. The main result is that convergence can be specified in terms of the number of grains surrounding a region of interest.

A thermally-activated constitutive model is developed based on dislocation interactions, crystallographic orientations and microstructural evolution to describe the elasto-plastic stress strain behavior during multi-axial loading. The aim is to contribute to the quantification of complex strain path response in solid solution strengthened alloys. In detail, dislocation/dislocation interactions are incorporated in the model to quantify latent and kinematic hardening phenomena during loading path changes. Dislocation density-based constitutive relations are included to account for dislocation features such as dislocation forests, walls and channels. Moreover, dislocation/solute atom interactions are also considered in order to account for both dynamic and static strain aging as well as static recovery. The model is validated against multiple multi-axial data sets for AA5754-0 with changes of loading path and various degrees of pre-strain and time intervals between tests. (C) 2014 Elsevier Ltd. All rights reserved.

Atomistic simulations using the embedded atom method were employed to compute the energies of 408 distinct grain boundaries in bcc Fe and Mo. This set includes grain boundaries that have tilt, twist, and mixed character and coincidence site lattices ranging from Sigma 3 to Sigma 323. The results show that grain boundary energies in Fe and Mo are influenced more by the grain boundary plane orientation than by the lattice misorientation or lattice coincidence. Furthermore, grain boundaries with (110) planes on both sides of the boundary have low energies, regardless of the misorientation angle or geometric character. Grain boundaries of the same type in Fe and Mo have strongly correlated energies that scale with the ratio of the cohesive energies of the two metals. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

We describe a methodology for calculating approximate, yet accurate analytical expressions for the probability density function of grain diameter as obtained from experimental microstructures. This methodology relies on a novel cumulant expansion that is tailored to the lognormal distribution and provides a systematic description of departures from lognormality. We test our methodology by characterizing two data sets obtained from the microstructures associated with polycrystalline, high-purity Al2O3 samples. The utillity of this approach is demonstrated by a detailed statistical analysis. (C) 2015 Elsevier B.V. All rights reserved.