Anisotropic electrical properties in thermal spray metallic coatings

Direct current resistivity of freestanding metallic coatings of Ni–Al alloys made by a variety of thermal spray processes was measured in-plane (=ρip) and through-thickness (=ρtt), using a four-contact method. The coatings exhibited anisotropic resistivities with anisotropy (=ρtt/ρip) ranging from 1.1 to 2.2 across the processes. Results are analyzed in the context of coating microstructures and chemical compositions obtained by electron microscopy. In addition, a simple electric circuit analysis approximating the coating as brick-layer structure illustrates the significance of splat interfaces to electrical behavior.