Microstructural Evolution and Sintering of Suspension Plasma-Sprayed Columnar Thermal Barrier Coatings

Omkar Aranke,Björn Kjellman,Mohit Gupta,Xin-Hai Li,Nicolaie Markocsan

doi:10.1007/s11666-018-0778-z

Omkar Aranke, Björn Kjellman + Show 3 more

Open Access

https://doi.org/10.1007/s11666-018-0778-z

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Abstract

Suspension plasma spray (SPS) is capable of producing coatings with porous columnar structure, and it is also a much cheaper process compared to the conventionally used electron beam physical vapor deposition (EB-PVD). Although TBCs with a columnar microstructure that are fabricated using SPS have typically lower thermal conductivity than EB-PVD, they are used sparingly in the aerospace industry due to their lower fracture toughness and limited lifetime expectancy. Lifetime of TBCs is highly influenced by the topcoat microstructure. The objective of this work was to study the TBCs produced using axial SPS with different process parameters. Influence of the microstructure on lifetime of the coatings was of particular interest, and it was determined by thermal cyclic fatigue testing. The effect of sintering on microstructure of the coatings exposed to high temperatures was also investigated. Porosity measurements were taken using image analysis technique, and thermal conductivity of the coatings was determined by laser flash analysis. The results show that axial SPS is a promising method of producing TBCs having various microstructures with good lifetime. Changes in microstructure of topcoat due to sintering were seen evidently in porous coatings, whereas dense topcoats showed good resistance against sintering.

Highlights

Thermal barrier coatings (TBCs) are used to protect the metallic components which are used in the hot sectors of the gas turbines
The development of TBCs fabricated by suspension plasma spray (SPS) is of high commercial interest as Suspension plasma spray (SPS) is capable of producing coatings with strain-tolerant columnar microstructure similar to the conventional electron beam physical vapor deposition (EB-PVD) process (Ref 4, 5)
Lower costs with SPS imply that SPS can be used as a replacement of EB-PVD but it could be used for a variety of components in gas turbines including components where less strain-tolerant APS coatings were employed earlier due to lower costs, and more importantly, the existing infrastructure for APS can be utilized making it a potentially widely available technology

Summary

Introduction

Thermal barrier coatings (TBCs) are used to protect the metallic components which are used in the hot sectors of the gas turbines. TBCs having better functional performance will allow higher operating temperatures resulting in complete fuel combustion in the gas turbine engines delivering higher efficiency along with lower emissions (Ref [1,2,3]). The development of TBCs fabricated by suspension plasma spray (SPS) is of high commercial interest as SPS is capable of producing coatings with strain-tolerant columnar microstructure similar to the conventional electron beam physical vapor deposition (EB-PVD) process (Ref [4, 5]). It is well known that TBCs produced using SPS can have lower thermal conductivity than other conventional processes due to a highly porous microstructure (Ref [6,7,8]). Lower costs with SPS imply that SPS can be used as a replacement of EB-PVD but it could be used for a variety of components in gas turbines including components where less strain-tolerant APS coatings were employed earlier due to lower costs, and more importantly, the existing infrastructure for APS can be utilized making it a potentially widely available technology

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