At present, microstructural characterisation is still largely relied on 2D imaging of electronic microscopies, which has intrinsic spatial limitation. A typical example is the examination of the distribution of small size particles inside the much larger matrix grains. In most case, the 2D cross-sectional image cannot completely reveal those particles that were “buried” in the grains.
In this work, we applied the 3D-FIB tomographic technique in a FEI Dual FIB/SEM-SCIOS milling system to examine the spatial distribution of LaB6 nanoparticles in an Al-Si alloy fabricated by metal 3D-printing. A volume of 9 × 8 × 8 μm from a MP was serially sectioned into 20 nm thick slices and a series SEM backscattered electron (SEM-BE) images were taken after removing each slice. The image stack was subsequently aligned, followed by sequential segmentation and reconstruction using Amira™. The reconstruction image clearly show the homogeneous distribution of the LaB6 nanoparticles in the alloy. Moreover, although some LaB6 nanoparticles are segregated along the Al grain boundaries, each Al grain contains at least one LaB6 nanoparticle. From the solidification view point, this result provides direct evidence demonstrating that all Al grains nucleate on the LaB6 nanoparticles during solidification process.
This work demonstrates the feasibility of 3D-FIB tomographic analysis in characterising the spatial distribution of nanoparticles within microstructures. It is believed that this technique can be implemented to other microstructural characterisations, such as the shape and fraction of microstructures and defects, which cannot be realized in 2D imaging.
University of Queensland