Abstract No.:
5483

 Scheduled at:
Wednesday, June 07, 2017, Hall 28 2:40 PM
Equipment / Consumables & Powders, Wires, Suspensions I


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

 Authors:
Lutz-Michael Berger* / Fraunhofer IKTS, Germany
Robert Vaßen/ FZ Jülich, IEK-1, Germany
Yoo Jung Sohn/ FZ Jülich, Germany

 Abstract:
In the binary Al2O3-TiO2 system exists the compound Al2TiO5 (aluminum titanate), which melts congruently but decomposes at temperatures below 1200 °C. However, it can appear both in the feedstock powders and in the coatings, if the cooling rates are high enough. Its properties (e.g. thermal conductivity, CTE) differ significantly from those of Al2O3 and TiO2. Thus it is of special interest to study the stability of Al2TiO5 in the spray process starting from feedstock powders with different compositions, as well as the coating properties.
A commercial fused and crushed Al2O3-40%TiO2 was selected as the feedstock material for the experimental work presented in this contribution, as the composition is close to the composition of Al2TiO5. Part of the powder was heat-treated in air at 1150° and 1550°C in order to vary the phase composition, while not influencing the particle size distribution and processability. The powder was analyzed by thermal analysis, XRD and FESEM including metallographically prepared cross sections. The original powder was found to be substoichiometric, a hydrogen atmosphere leads to further reduction. A powder consisting of Al2TiO5 only was not possible to be prepared due to inhomogeneous distribution of Al and Ti in the original powder.
Plasma spraying was performed with a Triplex gun (Oerlikon Metco) using Ar-H2 and Ar-He plasma gas mixtures. Coatings were studied by XRD, REM of metallographically prepared cross sections, and microhardness HV1. Coatings sprayed with the Ar-H2 plasma showed a higher hardness. Moreover, the results show a clear influence of the Al2TiO5 content in the feedstock powder on the phase composition of the coatings.


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