Atmospheric Plasma Spraying of High Melting Temperature Complex Perovskites for TBC Application
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M.O. Jarligo, D.E. Mack, G. Mauer, R. Vaßen, and D. Sto¨ver (Submitted April 30, 2009; in revised form July 14, 2009) High melting materials have always been very attractive candidates for materials development in thermal barrier coating (TBC) applications. Among these materials, complex perovskites with Ba(Mg1/3Ta2/3)O3 and La(Al1/4Mg1/2T1/4)O3 compositions have been developed and deposited in TBC systems by atmospheric plasma spraying. Spray parameters were optimized and in-flight particle temperatures were recorded using Accuraspray-g3 and DPV 2000. Plasma sprayed coatings were found to undergo nonstoichiometric decomposition of components which could have contributed to early failure of the coatings. Particle temperature diagnostics suggest that gun power of ~15 kW or lower where majority of the particles have already solidified upon impact to the substrate could probably prevent the decomposition of phases. Additionally, it has been found that the morphology of the powder feedstock plays a critical role during atmospheric plasma spraying of complex perovskites.
Keywords
atmospheric plasma sprayed (APS) coatings, gas turbine coatings, particle diagnostics, perovskite ceramics
1. Introduction One of the most essential requirements for advanced thermal barrier coating (TBC) materials of gas-turbine engines is phase stability at extremely high operation temperature (~1300 C), in order to improve the engine efficiency and performance (Ref 1). The most promising candidates for materials development, therefore, are those with high melting temperatures in addition to phase stability and low thermal conductivity in general. Among these materials, AB01=3 B002=3 O3 complex perovskite in particular with Ba(Mg1/3Ta2/3)O3 (BMT) composition has melting temperature of ~3000 C and is considered among the most refractory oxides ever known to science (Ref 2, 3). This complex perovskite has a B-site cation dependent
This article is an invited paper selected from presentations at the 2009 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Expanding Thermal Spray Performance to New Markets and Applications: Proceedings of the 2009 International Thermal Spray Conference, Las Vegas, Nevada, USA, May 4-7, 2009, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2009. M.O. Jarligo, D.E. Mack, G. Mauer, R. Vaßen, and D. Sto¨ver, Institut fu¨r Energieforschung (IEF-1), Forschungszentrum Ju¨lich GmbH, Ju¨lich, Germany. Contact e-mail: m.o.jarligo@ fz-juelich.de.
Journal of Thermal Spray Technology
dual crystal structure which the material may adopt to maintain chemical stability, making it unique from other perovskites (Ref 3, 4). The B0 and B00 cations can exhibit 1:2 ordering along the [111] axis forming a hexagonal P 3m1 space group symmetry typically found in well sintered ceramics. In some cases, the non-stoichiometric 1:1 ordering is preferred leading to
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