C.R. Weinberger's research while affiliated with Drexel University and other places

Disclinations, defects that accommodate rotational incompatibilities in a crystal lattice, have been described in detail in the literature, but rarely observed in solid materials. Recently, a method has been described by which it is proposed that disclination densities can be estimated using spatially resolved orientation data generated from electron backscatter diffraction or precession electron diffraction. Herein, a rigorous evaluation of this approach is performed. In this work, a series of constructed and real data sets are used to evaluate the methodology for estimating disclination densities from spatially mapped orientation data and demonstrate the inherent error associated with this approach. It is shown that the outcome of this analysis is heavily dependent on the how numerical approximations are implemented. If a self-consistent method is used, then the disclination tensor will always be zero and if an inconsistent method is used then the error in the estimation of the disclination tensor is unbounded. Therefore, although the theory behind the disclination tensor is sound, the inputs needed to calculate it are not experimentally accessible through the application of numerical approximation methods to orientation maps and a different methodology is needed.

div class="title">Nye Tensor Dislocation Density Mapping From Precession Electron Diffraction: Effects of Filtering and Angular Resolution - Volume 21 Issue S3 - A.C. Leff, C.R. Weinberger, M.L. Taheri

The Nye tensor offers a means to estimate the geometrically necessary dislocation density of a crystalline sample based on measurements of the orientation changes within individual crystal grains. In this paper, the Nye tensor theory is applied to precession electron diffraction automated crystallographic orientation mapping (PED-ACOM) data acquired using a transmission electron microscope (TEM). The resulting dislocation density values are mapped in order to visualize the dislocation structures present in a quantitative manner. These density maps are compared with other related methods of approximating local strain dependencies in dislocation-based microstructural transitions from orientation data. The effect of acquisition parameters on density measurements is examined. By decreasing the step size and spot size during data acquisition, an increasing fraction of the dislocation content becomes accessible. Finally, the method described herein is applied to the measurement of dislocation emission during in situ annealing of Cu in TEM in order to demonstrate the utility of the technique for characterizing microstructural dynamics. Copyright © 2015 Elsevier B.V. All rights reserved.