Abstract
Porosity is a key feature of thermally-sprayed coating microstructure. Porosity is made of pores and cracks of various orientations. Both pores and cracks can be intralamellar or interlamellar due to coating build-up which leads to lamellae from impinging of droplets. Pores are interconnected with cracks, which results in a 3-dimensional porosity network. Direct observation of this network is intricate and remains somewhat limited. A 3-dimensional simulation of this network was therefore developed in this work based on the building-up of objects which simulated the lamellae in the sprayed microstructure. These objects were constructed from morphological measurements using confocal microscopy of actual lamellae, i.e. “splats”, obtained from “linescan”-typed plasma-sprayed experiments. This simulation, in the lamella building-up, involves randomly cracks and pores the characteristics of which (i.e. content, orientation, size, …) were determined from thorough quantitative image analysis of cross-section plasma-sprayed alumina microstructures. Using 3-dimensional images resulting from the simulation, finite element calculations were performed to study dielectric properties of plasma-sprayed alumina as a function of porosity. The influence of anisotropy is discussed in particular and calculated values compared to experimental values.
