Effect of Heat Treatment on Microstructure and Thermal Conductivity of Thermal Barrier Coating.

Kyomin Kim,Woochul Kim

doi:10.3390/ma14247801

Abstract

Thermal barrier coatings (TBCs) are essential for increasing the inlet temperature of gas turbines to improve their thermal efficiency. Continuous exposure to flames is known to affect the thermal properties of TBCs, degrading the performance of gas turbines as a consequence. In this study, we quantified the changes in the thermal conductivity of yttria-stabilized zirconia coatings with respect to various heat treatment temperatures and times. The coating exhibited an increase in thermal conductivity after heat treatment, with higher heat treatment temperatures resulting in greater thermal conductivity. The coatings were analyzed by X-ray diffraction and scanning electron microscopy before and after heat treatment. Results showed that there was little change in thermal conductivity due to phase changes and grain size. We conclude that pore structures, i.e., circular and lamellar pores, affected the change in thermal conductivity. Specifically, we confirmed that the change in thermal conductivity depends on the size of the lamellar pores.

Highlights

Heat Treatment on MicrostructureThe development of thermal barrier coatings (TBCs) has improved the durability of gas turbine components exposed to high temperatures and has improved the energy efficiency of gas turbines by increasing the turbine inlet temperature [1]
The change in thermal conductivity of 7YSZ coating manufactured by air plasma spray (APS) was analyzed with respect to several heat treatment conditions
The coatings were heat-treated at 1150 and 1200 ◦ C, and their thermal conductivity increased as the heat treatment temperature increased

Summary

Introduction

The development of thermal barrier coatings (TBCs) has improved the durability of gas turbine components exposed to high temperatures and has improved the energy efficiency of gas turbines by increasing the turbine inlet temperature [1]. The temperature of the turbine inlet cannot be increased indefinitely due to the maximum operating temperature of the superalloy. Low thermal conductivity is essential for TBCs, to prevent oxidation and corrosion of superalloys at high turbine inlet temperatures. Yttria-stabilized zirconia (YSZ) is a commonly used top coating because it is capable of maintaining a constant low thermal conductivity even at high temperatures [5]. An increase in the yttria content results in lower thermal conductivity of the TBC. The amount of yttria content should be within an appropriate range because it can affect the thermal cycle stability.

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