Dynamic interactions of ingested molten silicate particles with air plasma sprayed thermal barrier coatings
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Dynamic interactions of ingested molten silicate particles with air plasma sprayed thermal barrier coatings Edward J. Gildersleeve Va) , Sanjay Sampath Center for Thermal Spray Research, Stony Brook University, Stony Brook, New York 11794-2275, USA a) Address all correspondence to this author. e-mail: [email protected] Received: 10 April 2020; accepted: 14 July 2020
Air plasma sprayed thermal barrier coatings (TBCs) are used extensively throughout the gas turbine industry for both power and propulsion. As these engines push to higher temperatures, concern for failure from the melt infiltration of ingested siliceous debris [commonly called calcium–magnesium–alumino-silicate (CMAS)] arises, especially in aeroengines. 7 wt% yttria-stabilized zirconia is particularly prone to melt infiltration and stiffeninginduced premature failure. Novel TBC materials such as gadolinium zirconate have been introduced for their infiltration-inhibiting CMAS reactions. Past academic work has utilized ideal laboratory furnace environments to study these phenomena. In this work, the influence of TBC microstructure and chemistry on impinging molten CMAS injected via a burner rig is studied. An observational study of the impacted surfaces and location-specific cross-sectional analysis is reported. Results point toward the critical role of surface microstructure on the mobility and reactivity of the molten CMAS.
INTRODUCTION Air plasma sprayed (APS) ceramic thermal barrier coatings (TBCs) have been widely used in gas turbine engines for the last several decades as protectors of the underlying superalloy metallic substrate/component from the high heat loads of the inlet combusting gases [1,2,3,4,5,6,7]. These ceramic overlay coatings are deposited as highly defected layered microstructures arising from the rapid solidification of molten powder feedstock impinging a metallic substrate/component [8,9,10]. Ceramic oxides of particular interest in the field of TBCs have been of zirconia stabilized by other oxides such as yttria and ceria. The most prominent among these thermal barrier oxides being the yttria-zirconia materials. Since the mid-1970s, TBC application and research has focused primarily on the processing and development of the 7 wt% yttria-stabilized zirconia (7YSZ) TBC [1,4,11,12,13]. Despite its numerous advantages, as gas turbine engines push toward higher operating temperatures for the sake of increased efficiency, 7YSZ TBCs become increasingly susceptible to premature failure. This is a consequence of a number of factors. For instance, these TBCs are prone to phase degradation at prolonged high-temperature exposure. This leads to the progressive decomposition of the high-toughness nonequilibrium t′ phase into the weaker, more brittle monoclinic and cubic
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phases [13,14,15,16]. Concurrent with the phase instabilities of such TBCs, the increased engine operating temperatures have given rise to concern toward ingested particulates and debris. Engine-ingested siliceous debris, par
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