A Study on the Microstructural Characterization and Phase Compositions of Thermally Sprayed Al₂O₃-TiO₂ Coatings...

In this work, the alumina (Al₂O₃) and alumina-titania coatings with different contents of TiO₂, i.e., Al₂O₃-13 wt.% TiO₂ and Al₂O₃-40 wt.% TiO₂, were studied. The coatings were produced by means of powder and liquid feedstock thermal spray processes, namely atmospheric plasma spraying (APS), suspension plasma spraying (SPS) and suspension high-velocity oxygen fuel spraying (S-HVOF). The aim of the study was to investigate the influence of spray feedstocks characteristics and spray processes on the coating morphology, microstructure and phase composition. The results revealed that the microstructural features were clearly related both to the spray processes and chemical composition of feedstocks. In terms of phase composition, in Al₂O₃ (AT0) and Al₂O₃-13 wt.% TiO₂ (AT13) coatings, the decrease in α-Al₂O₃, which partially transformed into γ-Al₂O₃, was the dominant change. The increased content of TiO₂ to 40 wt.% (AT40) involved also an increase in phases related to the binary system Al₂O₃-TiO₂ (Al₂TiO₅ and Al_2-xTi_1+xO₅). The obtained results confirmed that desired α-Al₂O₃ or α-Al₂O₃, together with rutile-TiO₂ phases, may be preserved more easily in alumina-titania coatings sprayed by liquid feedstocks.