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Influence of feedstock powder modification by heat treatments on the properties of APS-sprayed Al2O3-40%TiO2 coatings

: Berger, Lutz-Michael; Sempf, Kerstin; Sohn, Yoo Jung; Vaßen, Robert


Journal of thermal spray technology 27 (2018), No.4, pp.654-666
ISSN: 1059-9630
ISSN: 1544-1016
Bundesministerium für Wirtschaft und Technologie BMWi
IGF; 19471 BG
Weiterentwicklung thermisch gespritzter Schichten im System Al2O3-TiO2
Journal Article
Fraunhofer IKTS ()
Al2O3-TiO2; Al2TiO5; APS; feedstock powder; phase transformation; microstructure

The formation and decomposition of aluminum titanate (Al2TiO5, tialite) in feedstock powders and coatings of the binary Al2O3-TiO2 system are so far poorly understood. A commercial fused and crushed Al2O3-40%TiO2 powder was selected as the feedstock for the experimental series presented in this paper, as the composition is close to that of Al2TiO5. Part of that powder was heat-treated in air at 1150° and 1500°C in order to modify the phase composition, while not influencing the particle size distribution and processability. The powders were analyzed by thermal analysis, XRD and FESEM including EDS of metallographically prepared cross sections. Only a maximum content of about 45 wt% Al2TiO5 was possible to obtain with the heat treatment at 1500°C due to inhomogeneous distribution of Al and Ti in the original powder. Coatings were prepared by plasma spraying using a TriplexPro-210 (Oerlikon Metco) with Ar-H2 and Ar-He plasma gas mixtures at plasma power levels of 41 and 48 kW. Coatings were studied by XRD, SEM including EDS linescans of metallographically prepared cross sections, and microhardness HV1. With exception of the powder heat-treated at 1500 °C an Al2TiO5-Ti3O5 (tialite-anosovite) solid solution Al2-xTi1+xO5 instead of pure Al2TiO5 existed in the initial powder and the coatings.