Estimation of dislocation density from precession electron diffraction data using the Nye tensor

Abstract

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.

The effect of length scale on the determination of geometrically necessary dislocations via EBSD continuum dislocation microscopy

“…The Nye-Kröner equations can be used with any method of local lattice measurement, including µXRD [15] and precession electron diffraction in a TEM [30]. In this paper, the distortion gradients required by CDM are extracted via EBSD.…”

Characterization at high spatial and angular resolutions of deformed nanostructures by on-axis HR-TKD

“…Note that TKD and HR-TKD are benefiting from the greatest sensitivity of the Kikuchi bands to the orientation as compared to diffraction spots. As pointed out by Leff et al [44] , a possible solution for the TEM-based techniques to improve the angular resolution would be to apply the DIC to the automated orientation mapping on Kikuchi patterns [22] .…”

Multiscale Characterization of Microstructure and Residual Strain Distribution in Additively Manufactured Inconel 625

“…A Nye tensor calculation results in GND density maps on the subgrain level when used with PED in the TEM or EBSD in the SEM [9]. The resulting dislocation density data allows for comparison of subgrain strain distribution found by HR-EBSD or PED to be compared to intragranular GND densities and cell substructures in non-equilibrium microstructures (Fig.…”