Rapid solidification of plasma sprayed advanced materials: nanostructure characterisation

Composite ZrB2-SiC materials offer well known resistance to ablation at high temperature. An inert plasma spraying technique was used to manufacture composite ZrB2-SiC as potential thermal protection systems for composite based substrates. Due to the rapid solidification experienced by sprayed droplets, amorphous and/or nanostructured phases can be formed; advanced characterization techniques are therefore required in order to collect all the necessary data for process/product optimisation. In addition, silicon carbide, selected for its contribution to the oxidation resistance of the ceramic coating, is well known to be considered as a non sprayable material, due to the lack of a stable liquid phase. In this paper two issues are investigated: the first is the use of advanced characterization techniques, such as high resolution scanning and transmission electron microscopy, for microstructural analysis of plasma sprayed coatings. The second is the evaluation of possible implications of rapid solidification processes in composite systems for which at least one liquid phase is not stable, but, at the same time, the development of eutectic-like structures results in the formation of nanostructured stable solid phases