Observation of high resolution microstructures in advanced thermal sprayed coatings and single deposited splats using ion beam milling

Abstract

Microstructures of the coatings and single deposited splats formed by advanced thermal spray processes have been investigated using two types of ion beam milling: one is broad argon ion beam for the cross-sectioning of thermal sprayed coatings in a cross section polisher and the other is focused gallium ion beam (FIB) for the cross-sectioning and transmission electron microscopy (TEM) sample preparation of single splats. The cross section of tungsten carbide cobalt (WC-Co) coatings fabricated by the polisher showed that it created a mirrored surface with minimized artifacts such as pull-outs of ceramic particles or smearing of pores which can be made by conventional metallographic preparations. A thin and locally re-thinned membrane of single nickel (Ni) splat was prepared by the FIB technique to observe the internal interface of particle/substrate in high resolution atomic scale images. It was found that the steel substrate was heavily deformed by the impact of a nickel particle with high kinetic and thermal energies. At the periphery region, the particle and the substrate were intimately bonded without any voids or gaps.