Failure Analysis of Multilayered Suspension Plasma-Sprayed Thermal Barrier Coatings for Gas Turbine Applications

M Gupta,N Markocsan,X.-H Li,R Rocchio-Heller,L Östergren,J Liu

doi:10.1007/s11666-017-0683-x

Abstract

Improvement in the performance of thermal barrier coatings (TBCs) is one of the key objectives for further development of gas turbine applications. The material most commonly used as TBC topcoat is yttria-stabilized zirconia (YSZ). However, the usage of YSZ is limited by the operating temperature range which in turn restricts the engine efficiency. Materials such as pyrochlores, perovskites, rare earth garnets are suitable candidates which could replace YSZ as they exhibit lower thermal conductivity and higher phase stability at elevated temperatures. The objective of this work was to investigate different multilayered TBCs consisting of advanced topcoat materials fabricated by suspension plasma spraying (SPS). The investigated topcoat materials were YSZ, dysprosia-stabilized zirconia, gadolinium zirconate, and ceria–yttria-stabilized zirconia. All topcoats were deposited by TriplexPro-210TM plasma spray gun and radial injection of suspension. Lifetime of these samples was examined by thermal cyclic fatigue and thermal shock testing. Microstructure analysis of as-sprayed and failed specimens was performed with scanning electron microscope. The failure mechanisms in each case have been discussed in this article. The results show that SPS could be a promising route to produce multilayered TBCs for high-temperature applications.

Highlights

Development of thermal barrier coatings (TBCs) allowing higher combustion temperatures is of great interest for all gas turbine manufacturers since it results in a more efficient combustion which in turn results in higher fuel efficiency as well as environmentally cleaner emissions
The single-layer topcoats yttriastabilized zirconia (YSZ) and dysprosia-stabilized zirconia (DySZ) shown in Fig. 1(a) and (b) exhibited a dense columnar structure looking similar to the vertically cracked microstructure typically produced by atmospheric plasma spraying (APS)
Single-layer and bilayer topcoat architectures deposited by suspension plasma spraying (SPS) for TBCs were investigated

Summary

Introduction

Development of thermal barrier coatings (TBCs) allowing higher combustion temperatures is of great interest for all gas turbine manufacturers since it results in a more efficient combustion which in turn results in higher fuel efficiency as well as environmentally cleaner emissions. At temperatures above 1200 °C, the YSZ coatings undergo sintering at a high rate and are susceptible to CMAS (calcium–magnesium–alumino-silicates) attack, both of which may significantly affect the TBC lifetime (Ref [3, 4]). New ceramic materials such as the pyrochlores, perovskites, and co-doped zirconia have been identified as alternative candidates to YSZ for high-temperature applications (Ref [5, 6]). These materials usually exhibit a lower fracture toughness and thermal expansion coefficient than YSZ (Ref 7) and some of them (e.g., gadolinium zirconate) have compatibility issues with the bondcoat

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Conclusion