Modelling of gas permeation through ceramic coatings produced by thermal spraying

An analytical model has been developed for simulation of gas permeation through thermal spray coatings, and for prediction of the permeability. The model is based on a geometrical representation of the coating microstructure. This involves thin splats, with limited inter-splat bridging, and microcracks within the splats. Important variables include the thickness (smallest dimension) of the inter-splat pores and intra-splat microcracks. Uniform values of these parameters are used in the model. Predicted permeabilities are compared with experimental data obtained using plasma-sprayed zirconia coatings, both in the as-sprayed state and after heat treatments sufficient to generate significant microstructural changes via sintering effects. In general, good agreement is obtained and it is concluded that the model constitutes a useful tool for exploration of gas permeation characteristics in coatings or layers produced by thermal spraying.