Al₂O₃-TiO₂ coatings deposition by intermixed and double injection SPS concepts

This work focuses on the study on the novel hybrid method of simultaneous spraying from two different materials (Al₂O₃ and TiO₂) by means of suspension plasma spraying (SPS) using submicron powder and water suspension. The goal was to attempt the deposition of intermixed alumina-titania coatings, namely: Al₂O₃ + 3 wt.% TiO₂, Al₂O₃ + 13 wt.% TiO₂, and Al₂O₃ + 40 wt.% TiO₂. Such compositions are already used but in the form of conventionally plasma sprayed coatings, with micrometer-sized powder. Meanwhile, the injection of feedstocks with submicron-sized particles has not been established yet. In particular, this paper uses two routes of feedstock injection, (i) with the use of an intermixed suspension and (ii) a double injection of separate suspensions. The attention was paid to the characterization of the feedstock materials, description of deposition parameters as well as the morphology, microstructure, and phase composition of the obtained coatings. Among all coatings, Al₂O₃ + 40 wt.% TiO₂ sprayed with double injection contained the most homogeneously distributed and melted splats. The results from this work demonstrate the possibility of coating deposition both by intermixed and double injection concepts but also the need for the further application-relevant optimization, related to the presence of intercolumnar gaps in the microstructure of the coatings.