Three-dimensional imaging of microstructural evolution in SEM-based nano-CT

Scanning electron microscopy (SEM) is a powerful and versatile technique for materials characterization and present in many laboratories. The integration of an X-ray target holder and detector allows expanding the modalities of SEM by X-ray imaging. These little hardware adaptations enable radiography or X-ray computed tomography (CT) to gain three-dimensional (3D) information about a sample to be investigated. Since SEM-based CT is a non-destructive technique, the method can also image time-dependent changes in microstructure. Presented is the ability of SEM-based nano-CT to image the microstructural evolution of an aluminum-germanium (AlGe32) alloy as a result of annealing. First, the non-destructive CT method is used for an overview scan to identify a hidden region of interest (ROI) in the sample volume at low resolution. The following FIB target preparation reveals the microstructure, which is stepwise annealed and investigated with SEM-based nano-CT at high resolution afterwards. The resulting reconstructed volumes gained from the laboratory-based system are visualized in 3D and show the morphology changes of microstructure. Quantitative analysis reveals grain coarsening and the formation of precipitations in the size of 300–1000 nm. These time-dependent processes are additionally correlated with hardness measurements of the Al alloy.