This study examines the fundamental reactions that occur in-ﬂight during the solution precursor plasma spraying (SPPS) of solutions containing Zr- and Y-based salts in water or ethanol solvent. The effect of plasma jet composition (pure Ar, Ar-H 2 and Ar-He-H 2 mixtures) on the mechanical break-up and thermal treatment of the solution, mechanically injected in the form of a liquid stream, was investigated. Observation of the size evolution of the solution droplets in the plasma ﬂow by means of a laser shadowgraphy technique, showed that droplet break-up was more effective and solvent evaporation was faster when the ethanol-based solution was injected into binary or ternary plasma gas mixtures. In contrast with water-based solutions, residual liquid droplets were always detected at the substrate location. The morphology and structure of the material deposited onto stainless steel substrates during single-scan experiments were characterised by SEM, XRD and micro-Raman spectroscopy and were shown to be closely related to in-ﬂight droplet behaviour. In-ﬂight pyrolysis and melting of the precursor led to well-ﬂattened splats, whereas residual liquid droplets at the substrate location turned into non pyrolysed inclusions. The latter, although subsequently pyrolysed by the plasma heat during the depo- sition of entire coatings, resulted in porous ‘‘sponge-like’’ structures in the deposit.
Engineering the Microstructure of Solution Precursor Plasma-Sprayed Coatings / G., Bertolissi; C., Chazelas; Bolelli, Giovanni; Lusvarghi, Luca; M., Vardelle; A., Vardelle. - In: JOURNAL OF THERMAL SPRAY TECHNOLOGY. - ISSN 1059-9630. - STAMPA. - 21:(2012), pp. 1148-1162. [10.1007/s11666-012-9789-3]