Al2O3 – ZrO2 Finely Structured Multilayer Architectures from Suspension Plasma Spraying

Since more than one decade, many works are devoted to the elaboration of finely structured layers by thermal spray technology. Indeed, due to the large volume fraction of the internal interfaces, coatings structured at the sub-micrometer scale should exhibit better properties than those, more conventional, structured at the micrometer scale. They could hence offer pertinent solutions to numerous emerging applications, in particular for energy production, energy saving, diffusion and environmental barriers, etc. Among the different possible routes to produce finely structured layers, suspension plasma spraying (SPS) seems to be a possible one. Indeed, SPS is an alternative to conventional Atmospheric Plasma Spraying (APS) aiming at manufacturing thinner layers (i.e., 10 to 100 µm) due to the specific size of the feedstock particles, from a few tens of nanometers to a few micrometers. It consists in mechanically injecting within the plasma flow a suspension. 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. The staking of resulting splats, which present a diameter ranging between 0.1 and 2 µm and, an average thickness from 20 to 300 nm, permits to elaborate finely structured layers. Moreover, it appears as a versatile process that is able to manufacture different coating architectures according to the operating parameters (suspension properties, injection configuration, plasma properties, spray distance, torch scan velocity, scanning step, etc.). This paper aims at presenting firstly the effects of spray parameters and their coupling on the final coating microstructures and secondly the possibility to manufacture by SPS in a reproducible manner different types of finely structured layers in terms of composition and architecture.