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Atomistic simulations are used to investigate how the stress required for homogeneous nucleation of partial dislocations in single crystal copper under uniaxial tension changes as a function of crystallographic orientation. Molecular dynamics is employed based on an embedded-atom method potential for Cu at 10 and 300 K. Results indicate that non-Schmid parameters are required to describe dislocation nucleation for certain single crystal orientations. Specifically, we find that the stereographic triangle can be divided into two regions: a region where dislocation nucleation is dominated by the conventional Schmid factor (the resolved shear stress in the direction of slip) and a region where dislocation nucleation is dominated by the normal factor (the resolved stress normal to the slip plane). A continuum relationship that incorporates Schmid and non-Schmid terms to correlate the stress required for dislocation nucleation over all tensile axis orientations within the stereographic triangle is presented. The significance of this work is that simulation results are cast into an atomistically inspired continuum formulation for partial dislocation loop nucleation in face-centered cubic single crystals.

Molecular dynamics (MD) and density functional theory (DFT) studies were performed to investigate the influence of vacancy defects on generalized stacking fault (GSF) energy of fcc metals. MEAM and EAM potentials were used for MD simulations, and DFT calculations were performed to test the accuracy of different common parameter sets for MEAM and EAM potentials in predicting GSF with different fractions of vacancy defects. Vacancy defects were placed at the stacking fault plane or at nearby atomic layers. The effect of vacancy defects at the stacking fault plane and the plane directly underneath of it was dominant compared to the effect of vacancies at other adjacent planes. The effects of vacancy fraction, the distance between vacancies, and lateral relaxation of atoms on the GSF curves with vacancy defects were investigated. A very similar variation of normalized SFEs with respect to vacancy fractions were observed for Ni and Cu. MEAM potentials qualitatively captured the effect of vacancies on GSF.

Serial sectioning methods continue to produce an abundant amount of image data for quantifying the three-dimensional nature of material microstructures. Here, we discuss a methodology to automate detecting and characterizing eutectic particles taken from serial images of a production turbine blade made of a heat-treated single crystal Ni-based superalloy (PWA 1484). This method includes two important steps for unassisted eutectic particle characterization: automatically identifying a seed point within each particle and segmenting the particle using a region growing algorithm with an automated stop point. Once detected, the segmented eutectic particles are used to calculate microstructural statistics for characterizing and reconstructing statistically representative synthetic microstructures for single crystal Ni-based superalloys. The significance of this work is its ability to automate characterization for analysing the 3D nature of eutectic particles.

Computer-generated 2D microstructures of varying second phase area fraction (5–30%), aspect ratio (1–16) and degree of alignment (where the reinforcement major-axis orientation is random, perfectly aligned or semi-aligned) are analyzed via the isotropic and directional forms of the computationally efficient multi-scale analysis of area fractions (MSAAF) technique. The impact of these microstructure parameters on the representative volume element (RVE) necessary to characterize a microstructure is ascertained with variations in isotropic and directional homogeneous length scales, derivative quantities of the MSAAF technique. Analysis of these results produces empirical expressions for the directional homogeneous length scale as a function of area fraction and aspect ratio for the limiting cases of random and 'perfect' second phase alignment. Generally, particle alignment is observed to increase the aspect ratio of a microstructure's RVE—a trend amplified by higher reinforcement aspect ratios and lower area fractions. Particle alignment also decreases the absolute size of such an element by reducing the directional homogeneous length scales transverse to the axis of alignment. Periodic boundary conditions on the perimeter of the synthetic microstructures are used to characterize the error in the MSAAF technique via multiple instantiations of the same microstructure, which further indicates that the statistical variation in the directional homogeneous length scale (measured by the directional MSAAF technique) can be an order of magnitude less than the variation in the isotropic homogeneous length scale (measured by the isotropic MSAAF technique).