Thick ceramic thermal barrier coatings with high durability deposited using solution-precursor plasma spray

Abstract

The efficacy of ceramic thermal barrier coatings (TBCs) used to protect and insulate metal components in engines increases with the thickness of the TBCs. However, the durabilities of thick TBCs deposited using conventional ceramics-coating deposition methods have not been adequate. Here, we demonstrate the feasibility of depositing highly durable, 4 mm thick TBCs of ZrO 2–7 wt.% Y 2O 3 (7YSZ) on bond-coated superalloy substrates using the solution-precursor plasma spray (SPPS) method. It was found that the average thermal cycling life of the 4 mm thick SPPS TBCs is 820 cycles. While most of the conventional air plasma-sprayed (APS) coatings of the same composition and thickness deposited on identical bond-coated superalloy substrates were found to be detached partially from the substrates in the as-sprayed condition, the APS TBC that was intact failed after 40 thermal cycles. The dramatic improvement in the thermal cycling life in the SPPS TBCs can be attributed to: (i) the significantly higher in-plane indentation-fracture toughness (over five-fold) in the SPPS TBCs over APS TBCs and (ii) the presence of the vertical cracks in SPPS TBCs resulting in a high degree of strain tolerance. The large thickness of the SPPS coatings also allowed us to characterize the mechanical properties of the ceramic top-coat in some detail. To that end, we report here the results from indentation-toughness tests and uniaxial-compression tests on the SPPS TBCs and the reference APS TBCs.