Formation and Stability of Al2TiO5 in Al2O3-40% TiO2 APS Coatings

The formation and decomposition of aluminum titanate (Al₂TiO₅) in coatings of the Al₂O₃-TiO₂ system are of high importance due to the significant differences between the physical properties of this compound and the single oxides Al₂O₃ and TiO₂. This is in relevant for the commercial feedstock Al₂O₃-40% TiO₂ having a composition close to Al₂TiO₅. In our previous study it was shown that the homogeneity of distribution of Al and Ti in the feedstock powder plays an essential role. Accordingly, in this study we used a commercial powder with a high Al₂TiO₅ content. A thermal treatment at 1150 °C resulted in a modified powder consisting of Al₂O₃ and TiO₂ only without changing the powder morphology and particle size distribution. Both powders were sprayed by APS using an F4 with Ar/H₂ plasma. Surprisingly, the reformation of Al₂TiO₅ for the modified powder was observed. The microstructures and some selected properties (electrical resistivity, chemical stability against sulphuric acid, etc.) of the coatings prepared from these powders are studied and discussed. These properties are also discussed in comparison with properties of coatings prepared from other feedstock powders of the same composition.