Effects of Syngas Particulate Fly Ash Deposition on the Mechanical Properties of Thermal Barrier Coatings on Simulated Film-Cooled Turbine Vane Components

Abstract

Research is being conducted to study the effects of particulate deposition from contaminants in coal synthesis gas (syngas) on the mechanical properties of thermal barrier coatings (TBC) employed on integrated gasification combined cycle (IGCC) turbine hot section airfoils. West Virginia University (WVU) had been working with US Department of Energy, National Energy Technology Laboratory (NETL) to simulate deposition on the pressure side of an IGCC turbine first stage vane. To model the deposition, coal fly ash was injected into the flow of a combustor facility and deposited onto TBC coated, angled film-cooled test articles in a high pressure (approximately 4 atm) and a high temperature (1560 K) environment. To investigate the interaction between the deposition and the TBC, a load-based multiple-partial unloading micro-indentation technique was used to quantitatively evaluate the mechanical properties of materials. The indentation results showed the Young's Modulus of the ceramic top coat was higher in areas with deposition formation due to the penetration of the fly ash. This corresponds with the reduction of strain tolerance of the 7% yttria-stabilized zirconia (7YSZ) coatings.

Microstructural Degradation of Thermal Barrier Coatings on an Integrated Gasification Combined Cycle (IGCC) Simulated Film-Cooled Turbine Vane Pressure Surface Due to Particulate Fly Ash Deposition

“…The molten fly ash does have similar degradation to the ceramic top coat tips as the molten glass from CMAS. The reprecipitated YSZ columnar tips, along with the stress mismatch caused by the molten deposit, may have attributed to the strain tolerance loss found in the study of the mechanical properties of the test samples [15]. Further penetration of the deposition and heat treatment can result in floating YSZ in the deposits leading to the appearance of globular particles found in studies by Levi et al [3] and Peng et al [16].…”

“…SEM micrographs of the top view of unexposed and exposed YSZ coatings are shown in Figure 5 [15]. Figure 5(a) shows the top view of an unexposed, as-deposited YSZ coating on test sample 2-1.…”

“…Prior to any SEM and EDS work, the samples undergo a micro-indentation procedure on the ceramic top coat to evaluate the effects on the mechanical properties from the fly ash deposition. The study found that the modulus of elasticity increases in areas where the molten deposition had cooled and adhered onto the top coating [15]. The increase in the surface stiffness can be directly related to the reduction in strain tolerance of the YSZ coating.…”

“…The test articles used in this study are labeled and shown in Figure 2 [15] The test article most heavily infiltrated was the 20-degree angled test article 1 (see Figure 2(a)). Figure 2(b) & Figure 2(c) contains images of the unexposed 20-degree angled test article 2 and the exposed 10-degree angled test article 3 respectively.…”

“…The sectioning job produced flat test samples with an approximate thickness of 1/4 inches. Figure 3 details the sample labels for each test article [15]. The heavy deposition on test article 1 is outlined in Figure 3(a).…”