In this study, we investigated microstructures of thermal sprayed coatings and single deposited splats using two types of ion beam milling: one is argon ion beam for the cross-sectioning of thermal sprayed coatings in a cross section polisher, the other is gallium focused ion beam for the cross-sectioning and TEM sample preparation of single deposited splats. The cross section of WC-Co coatings fabricated by the polisher showed that it created a mirrored surface with minimizing artifacts such as pull-outs of ceramic particles or smearing of pores during conventional metallographic preparations. A thin and locally re-thinned membrane of single warm-sprayed nickel splat was feasible to observe the internal interface of particle/substrate in high resolution electron images. The substrate was heavily deformed by the impact of nickel particle with high kinetic and thermal energies. The particle and the substrate were intimately bonded without any voids or gaps.