One of the goals of this study is to better understand how suspension plasma spraying parameters, particularly plasma gas mixtures, influence layer formation. Another goal is to produce finely structured layers of Al 2 O 3 -ZrO 2 with a wide range of architectures. To that end, a simple theoretical model is used to describe the operating conditions of the plasma torch and the influence of spraying parameters is expressed in terms of the shape and size of spray beads.

Suspension plasma spraying (SPS) is a fairly recent technology that is able to process sub-micrometric-sized feedstock particles and permits the deposition of layers thinner (from 5 to 50 µm) than those resulting from conventional atmospheric plasma spraying (APS). SPS consists in mechanically injecting within the plasma flow a liquid suspension of particles of average diameter varying between 0.02 and 1 µm. Upon penetration within the DC plasma jet, two phenomena occur sequentially: droplet fragmentation and evaporation. Particles are then processed by the plasma flow prior their impact, spreading and solidification upon the surface to be covered. Depending upon the selection of operating parameters, among which plasma power parameters (operating mode, enthalpy, spray distance, etc.), suspension properties (particle size distribution, powder mass percentage, viscosity, etc.), and substrate characteristics (topology, temperature, etc.), different coating architectures can be manufactured, from dense to porous layers. Nevertheless, the coupling between the parameters controlling the coating microstructure and properties are not yet fully identified. The aim of this study is to further understand the influence of parameters controlling the manufacturing mechanisms of SPS alumina coatings, in particular the spray patterns influence.