Durability of plasma sprayed thermal barrier coatings with controlled properties part I: For planar disk substrates

• Published in: Surface & coatings technology Vol. 424; p. 127678
• Main Authors: Gildersleeve V, Edward J., Sampath, Sanjay
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 25.10.2021; Elsevier BV
• Subjects: Air plasma; Coatings; Delamination; Durability; Elastic limit; Elastic Strain Energy; Failure mechanisms; Furnace Cycle Testing (FCT); Literature reviews; Mathematical analysis; Mechanical properties; Microstructure; Microstructure-porosity-performance relationships; Porosity; Sintering; Sintering (powder metallurgy); Stiffness; Strain; Substrates; Superalloys; Temperature gradients; Thermal barrier coatings; Thermal Barrier Coatings (TBCs); Trends; Turbines; Elastic Strain Energy; Thermal Barrier Coatings (TBCs); Furnace Cycle Testing (FCT); Microstructure-porosity-performance relationships; Sintering
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2021.127678

Thermal Barrier Coatings (TBCs) have been qualified for their thermo-mechanical performance and durability using Furnace Cycle Testing (FCT) for decades. FCT provides guidance toward materials and process improvements. Although FCT is a relatively straightforward test, the interpretation can often be subject to uncertainty, making it difficult to link test results directly to engine performance. This is because in FCT, the coating and substrate are isothermally treated, while real turbine components experience strong thermal gradients and time transients. Gradient testing can be time-consuming and expensive, thus FCT tests provide a cost-effective first-order confidence screening for development. A review of the available literature on Air Plasma Spray (APS) TBC durability by FCT does not reveal consistent trends among processing, microstructure (i.e., porosity), and durability. Furthermore, the available literature does not comprehensively capture the influence of microstructural changes (i.e., sintering) on FCT durability. In this two-part study, APS TBCs were produced with systematically-controlled microstructures, using multiple powder types on different bond-coated superalloy substrates and subjected to different FCT conditions. In Part I, the focus is on disk specimens, where edge-delamination failure predominates, while Part II will address curved surfaces with different failure mechanisms. The FCT results for the systematically produced coatings suggest marginal trends between durability and porosity of APS TBCs, with denser/tougher microstructures providing more durable outcomes, i.e., segmented coatings. One coating was sprayed multiple times over six years and tested in FCT to benchmark the durability testing and coating process reproducibility at Stony Brook. The results were compiled in a unified framework, utilizing published formulations to calculate available elastic strain energy, which serves as a driving force for delamination. The current results highlight a few regimes of FCT performance based on coating toughness, stiffness, and nonlinear elastic parameters. In addition, the benefits and limitations of FCT are discussed in this study. •Plasma-sprayed YSZ TBCs were studied systematically for their FCT durability.•Over 6 years, one YSZ TBC was sprayed and generated reproducible FCT durability.•HOSP and Agglomerated & Sintered TBCs were evaluated for their FCT durability.•Elastic Energy analysis revealed durability trends that were otherwise not obvious.•Flash Thermography showed highly porous TBCs resist constrained sintering.