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Precipitates and their associated strain fields significantly influence mechanical properties and, consequently, the industrial performance of aluminum alloys. In this work, we present a direct measurement of strains induced by η′ and η precipitates in an Al-Zn-Mg-Cu alloy using aberration-corrected high-resolution transmission electron microscopy and quantitative strain analysis. The results demonstrate that the strain induced by precipitates in the Al-Zn-Mg-Cu alloy shows significant tensile strains perpendicular to the longitudinal direction of the precipitate discs on the side of the discs and along the longitudinal direction at both ends of the η′ and η precipitates. This strain field can be described by an equivalent dislocation model, in which the lattice mismatch between the precipitate and the matrix is equivalent to a series of dislocation pairs along the precipitate/matrix interfaces. [ABSTRACT FROM AUTHOR]

Abstract: The accuracy of maximum entropy reconstruction of Z-contrast STEM images has been evaluated with the effects of experimental variables and noise taken into account by the means of image simulation. As the specimen contains atom species of greatly different atomic numbers, special attention is given to the reliability of the position and composition of lighter atoms that are determined from Z-contrast images in the presence of heavier atoms. When the noise is moderate (SNR >2.5), the position of atom columns can be measured within an accuracy of 0.03nm. With a higher signal-to-noise ratio (SNR >5) the composition of lighter atoms can be resolved reliably from the Z-contrast images. However, when image noise increases, the relative intensity of lighter atoms may deviate from the actual value in the specimen object function. [Copyright &y& Elsevier]

Abstract: Precise knowledge of crystal thickness and orientation is critical for reliable interpretation of high-resolution transmission electron micrographs. In this paper, we propose a criterion of S 2 (T, u, v), which measures the crystal thickness by intensity matching of the selected-area Fourier transform of experimental holograms with the calculated electron diffraction pattern at a series of trial thicknesses (T) and crystal tilts (u, v). This criterion has been demonstrated successfully for local thickness determination from a simulated high-resolution image of a wedge-shaped YBa2Cu3O7−δ and from an experimental hologram of a Si crystal. [Copyright &y& Elsevier]