Perspectives on Thermal Gradients in Porous ZrO2-7–8 wt.% Y2O3 (YSZ) Thermal Barrier Coatings (TBCs) Manufactured by Air Plasma Spray (APS)

Rogerio S Lima

doi:10.3390/coatings10090812

Abstract

Porous (~10–20%) ZrO2-7–8 wt.% Y2O3 (YSZ) thermal barrier coatings (TBCs) manufactured via air plasma spray (APS) and exhibiting a thickness range of ~250–500 µm, provide thermal insulation from the hot combustion gases to the metallic parts located in the hot stationary sections of gas turbine engines (e.g., combustion chambers of aerospace turbines). The objective of this paper was to measure and report the thermal gradient values in a benchmark porous (~15%) APS YSZ TBC, working within the known acceptable maximum temperature envelop conditions of a TBC/substrate system, i.e., T-ysz ~1300 °C and T-sub ~1000 °C. In order to accomplish this objective, the following steps were performed. A benchmark APS YSZ TBC exhibiting two distinct thicknesses (~260 and ~460 µm) was manufactured. In addition, a thermal gradient laser-rig was employed to generate a temperature drop (ΔT) along the coated coupon, with the target operate within the acceptable maximum temperature capabilities of this type of TBC/substrate architecture. This target was achieved, i.e., T-ysz values were not higher than ~1300 °C while the substrate temperatures did not reach values above ~1000 °C. The ΔTs for the ~260 and ~460 µm YSZ TBCs were ~280 and ~465 °C, respectively. The thermal gradient value for both YSZ TBCs was ~0.90 °C/µm, which falls within those reported in the literature for porous APS YSZ TBCs.

Highlights

Porous air plasma spray (APS) YSZ thermal barrier coatings (TBCs) Microstructures and Laser-Rig Thermal Gradient Setup laser-rig at setup and (iii) IR camera image after the thermal gradient started for the ~260 μm thick shows (i) the as-sprayed cross-sectional microstructure, (ii) snap-shot of sample in the (Figure 7a) andFigure
It is important to realize that these values are coming from two unique types thermal gradient rigs, which have been reported by independent R&D groups. This overall outcome of findings outlined from different teams is thought to be “surprisingly comparable” and, the results reported in this work are considered to be representative of porous APS YSZ TBCs
Benchmark porous (~15%) YSZ TBCs were manufactured via APS at two different YSZ thicknesses (~260 and ~460 μm) on the same bond-coated superalloy substrate

Summary

Introduction

Overall Characterics of Porous APS YSZ TBCs. Gas turbine engines have been widely employed in aerospace, power generation and marine applications. Gas turbine engines have been widely employed in aerospace, power generation and marine applications It is one of the most advanced and efficient engines ever engineered by mankind. Among the many critical components of gas turbines, this paper emphasizes the ones located in the static or stationary hot-sections, e.g., combustion chambers, vanes, ducts and afterburners. These components, made from Ni-based superalloys (melting point ~1300–1400 ◦ C), typically exhibit a wall thicknesses in the range of only ~1–2 mm. They are subjected to high heating flows resulting from the hot stream of the combustion gases, which can reach maximum temperatures of 2000 ◦ C at the flame core (primary zone) inside the combustion chamber [1,2]

Objectives

Methods

Results

Conclusion