Microstructural tomography of a Ni70Cr20Al10Ni70Cr20Al10 superalloy using focused ion beam microscopy

A focused ion beam (FIB) microscope has been used to simultaneously depth profile and image the γ–γ′γ–γ′ microstructure of a nickel base superalloy using normal incidence milling in order to characterize the precipitate microstructure in three dimensions (3D). The normal incidence milling rates of the γγ and γ′γ′ phases in this alloy are closely matched when the orientation of the depth-profiled surface is near 〈001〉, which allows for uniform material removal to depths up to a couple of microns. Depth-profiling experiments consisted of automated ion milling and collection of ion-generated secondary-electron images at specified intervals, and was demonstrated for a voxel resolution of roughly 15×15×16nm3. Image-processing software was used for automated processing of the 2D image sequence to render the γγ precipitate structure in 3D.