The present study is devoted to the creation of a process-structure-property database for dual phase titanium alloys, through a synthetic microstructure generation method and a mesh-free fast Fourier transform based micromechanical model that operates on a discretized image of the microstructure. A sensitivity analysis is performed as a precursor to determine the statistically representative volume element size for creating 3D synthetic microstructures based on additively manufactured Ti-6Al-4V characteristics, which are further modified to expand the database for features of interest, e.g., lath thickness. Sets of titanium hardening parameters are extracted from literature, and The relative effect of the chosen microstructural features is quantified through comparisons of average and local field distributions.

Three nickel electrodeposits with comparable grain size were synthesized by tailoring the cicctrodeposition conditions. Thorough microstructural characterizations including electron backscatter diffraction, ion channeling contrast imaging, electron channeling contrast imaging, transmission Kikuchi diffraction, transmission electron and high annular dark-field imaging were applied. The deposits contain a high density of twin boundaries with similar microstructures in terms of grain boundary character. These materials were annealed at various temperatures to study the microstructural evolution, and hence, their thermal stability. The differences in the character of twin boundaries and morphology of the grain boundaries in as-deposited state and their influence on the microstructural evolution at elevated temperatures are analyzed. The importance of incoherent twin boundaries, and the interaction of mobile general high angle boundaries with stationary boundaries are discussed. Finally, an optimal design for high thermal stability is proposed, based on the mechanisms that were inferred from the results. (C) 2018 Elsevier Ltd. All lights reserved.

The performance of electrochemical devices depends on the three-dimensional (3D) distributions of micro structural features in their electrodes. Several mature methods exist to characterize 3D microstructures over the microscale (tens of microns), which are useful in understanding homogeneous electrodes. However, methods that capture mesoscale (hundreds of microns) volumes at appropriate resolution (tens of nm) are lacking, though they are needed to understand more common, less ideal electrodes. Using serial sectioning with a Xe plasma focused ion beam combined with scanning electron microscopy (Xe PFIB-SEM), two commercial solid oxide fuel cell (SOFC) electrodes are reconstructed over volumes of 126 x 73 x 12.5 and 124 x 110 x 8 mu m(3) with a resolution on the order of approximate to 50(3) nm(3). The mesoscale distributions of microscale structural features are quantified and both microscale and mesoscale inhomogeneities are found. We analyze the origin of inhomogeneity over different length scales by comparing experimental and synthetic microstructures, generated with different particle size distributions, with such synthetic microstructures capturing well the high-frequency heterogeneity. Effective medium theory models indicate that significant mesoscale variations in local electrochemical activity are expected throughout such electrodes. These methods offer improved understanding of the performance of complex electrodes in energy conversion devices.

This study provides a general framework for the creation of three-dimensional microstructures for anisotropic two-phase materials with complex morphologies. The ability to create synthetic microstructures that are statistically representative of real materials is dependent on the ability of the generation algorithm to meet the assigned statistics. Hence, the fidelity of the synthetic microstructure depends on the efficiency of the generation process. The generated microstructures were statistically evaluated with respect to the target distribution for grain size, shape, orientation and phase volume fraction. This serves a dual purpose of validation of the packing algorithm and quantification of the 3D microstructures.

Relationships between prior beta grain size in solidified Ti-6Al-4V and melting process parameters in the Electron Beam Melting (EBM) process are investigated. Samples are built by varying a machine-dependent proprietary speed function to cover the process space. Optical microscopy is used to measure prior beta grain widths and assess the number of prior beta grains present in a melt pool in the raster region of the build. Despite the complicated evolution of beta grain sizes, the beta grain width scales with melt pool width. The resulting understanding of the relationship between primary machine variables and prior beta grain widths is a key step toward enabling the location specific control of as-built microstructure in the EBM process. Control of grain width in separate specimens and within a single specimen is demonstrated. (C) 2017 Elsevier B.V. All rights reserved.

The relationship between microstructure, dislocation motion and mechanical response of metallic multilayered nanomaterials is investigated. Several competing theories for the dependence of hardness on layer thickness, namely Confined Layer Slip (CLS) and Hall-Petch (H-P) theories are discussed. Analysis of homophase and heterophase experimental data suggests that Hall-Petch with modified coefficients provides a good fit down to layer thicknesses of about 5 nm, below which experimental data starts to deviate. We suggest that at this layer thickness, dislocations accumulate in the interface, and assuming there is a constant dislocation density in each interface, the strength varies as h(-1/2). (C) 2017 Published by Elsevier Ltd.