Microstructure modification of Y2O3 stabilized ZrO2 thermal barrier coatings by laser glazing and the effects on the hot corrosion resistance

Lei Guo,Fuxing Ye,Xinmu Zhang,Hui Xin,Zhao Zhang

doi:10.1007/s40145-020-0363-z

Lei Guo, Fuxing Ye + Show 3 more

Open Access

https://doi.org/10.1007/s40145-020-0363-z

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Abstract

Y2O3 stabilized ZrO2 (YSZ) thermal barrier coatings (TBCs) are prone to hot corrosion by molten salts. In this study, the microstructure of atmospheric plasma spraying YSZ TBCs is modified by laser glazing in order to improve the corrosion resistance. By optimizing the laser parameters, a ∼18 µm smooth glazed layer with some vertical cracks was produced on the coating surfaces. The as-sprayed and modified coatings were both exposed to hot corrosion tests at 700 and 1000 °C for 4 h in V2O5 molten salt, and the results revealed that the modified one had improved corrosion resistance. After hot corrosion, the glazed layer kept structural integrity, with little evidence of dissolution. However, the vertical cracks in the glazed layer acted as the paths for molten salt penetration, accelerating the corrosion of the non-modified coating. Further optimization of the glazed layer is needed in the future work.

Highlights

To improve the thermal efficiency and performance of turbine engines, thermal barrier coatings (TBCs) have been widely used on the hot section components of engines [1,2,3]
A TBC system consists of a ceramic top coat, commonly made of Y2O3 partially stabilized ZrO2 (YSZ), a metallic bond coat that is resistant to oxidation, a thermally grown oxide (TGO)
The formation mechanism for net-like/vertical cracks can be understand as follows: since the energy of a laser spot is unevenly distributed, the energy input and the solidification speed of the laser spot covered region are inhomogeneous during the laser treatment; as a result, a large stress could be created in the re-melted region, causing net-like/vertical cracks [33,34]

Summary

Introduction

To improve the thermal efficiency and performance of turbine engines, thermal barrier coatings (TBCs) have been widely used on the hot section components of engines [1,2,3]. YSZ coatings are sensitive to molten salt corrosion. Corrosive mediums react with YSZ, leaching out the stabilizer Y2O3. The coating transforms from a metastable tetragonal (t’) phase to a monoclinic phase, accompanied by a large volume expansion [13,14,15,16].

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