Emergence and impact of Al2TiO5 in Al2O3-TiO2 APS Coatings

Despite numerous studies and decades of industrial application, there is still a lack of understanding about the formation and the impact of aluminum titanate (Al2TiO5) in Al2O3-TiO2 thermal spray coatings. Especially the influence of the detailed feedstock powder characteristics on the phase composition has only crudely been investigated so far. Therefore, in this work we have quantified the Al2TiO5 content in three commercial Al2O3-TiO2 feedstock powders with 13 wt.% TiO2 and three powders with 40 wt.% TiO2. The effect of the varying phase compositions of the powders and their relevance for the properties and the phase compositions of the respective APS coatings was characterized in detail. While detrimental to the mechanical properties of 40 wt.% TiO2 coatings, we have found an enhancement of the hardness for 13 wt.% TiO2 coatings with an increasing Al2TiO5 content in the feedstock powder. Furthermore, it was found that Al2TiO5 may reform during APS when sprayed from an Al2TiO5-free powder