Structure determination of intermetallic phases in bulk Al alloys by 3D electron diffraction tomography

Abstract

Secondary phases in bulk metallic samples are difficult to characterize by conventional X-ray diffraction because the diffracted intensities are dominated by the contribution of the bulk material. Electron diffraction provides a better spatial resolution and one can obtain single crystal diffraction data from submicron sized precipitates. In this work we show that 3D electron diffraction tomography can yield diffraction data sets suitable for ab initio structure solution. We apply the recently proposed low-dose electron diffraction tomography method to 3 different phases in Al-based alloys: θ’-Al 2 Cu, Al 6 Fe and Al 4.5 FeSi. The structures of these phases were unambiguously determined even though there are other phases with similar chemical compositions and EDS analysis is not sufficient to distinguish them. • Intermetallics’ chemical composition can be too similar to be distinguished by EDS. • Intermetallics’ unit cell parameters can be too similar to be distinguished by SAED. • Precipitate phases can be unambiguously identified by 3D electron diffraction. • 3 phases of increasing complexity are identified.