Atomic-resolution chemical mapping of ordered precipitates in Al alloys using energy-dispersive X-ray spectroscopy. (May 2017)

• Record Type: Journal Article
• Authors: Wenner, Sigurd; Jones, Lewys; Marioara, Calin D.; Holmestad, Randi
• Is Part Of: Micron. Volume 96(2017)
• Page Start: 103
• Page End: 111
• Publication Date: 2017-05
• Subjects: Scanning transmission electron microscopy -- Energy-dispersive X-ray spectroscopy -- Aluminium alloys -- Precipitation; Microscopy -- Periodicals; Electron Probe Microanalysis -- Periodicals; Microscopy -- Periodicals; Microscopie -- Périodiques; Microscopy; Periodicals; 502.82
• DOI: 10.1016/j.micron.2017.02.007
• Languages: English
• ISSNs: 0968-4328

Abstract

Highlights: Beam-sensitive Al-alloy precipitates were chemically mapped with EDS. Non-rigid registration was applied to correct for drift and scan distortions. Chemical maps were achieved with atomic resolution and high signal-to-noise ratio. Local elemental substitution was observed in single atomic columns. Abstract: Scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDS) is a common technique for chemical mapping in thin samples. Obtaining high-resolution elemental maps in the STEM is jointly dependent on stepping the sharply focused electron probe in a precise raster, on collecting a significant number of characteristic X-rays over time, and on avoiding damage to the sample. In this work, 80 kV aberration-corrected STEM-EDS mapping was performed on ordered precipitates in aluminium alloys. Probe and sample instability problems are handled by acquiring series of annular dark-field (ADF) images and simultaneous EDS volumes, which are aligned and non-rigidly registered after acquisition. The summed EDS volumes yield elemental maps of Al, Mg, Si, and Cu, with sufficient resolution and signal-to-noise ratio to determine the elemental species of each atomic column in a periodic structure, and in some cases the species of single atomic columns. Within the uncertainty of the technique, S and β" phases were found to have pure elemental atomic columns with compositions Al2 CuMg and Al2 Mg5 Si4, respectively. The Q' phase showed some variation in chemistry across a single precipitate, although the majority of unit cells had a composition Al6 Mg6 Si7.2 Cu2 .