Effect of Vacuum Annealing on Microstructure and Hot-Salt Corrosion Behavior of CoNiCrAlY/YSZ/LaMgAl11O19 Double-Ceramic Coating

Guanming Xue,Zhiguo Wang,Yingchao Sun,Ling Xiang,Zhiwen Xie,Suying Hu

doi:10.3390/coatings11080951

Guanming Xue, Zhiguo Wang + Show 4 more

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https://doi.org/10.3390/coatings11080951

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Abstract

This study investigated the potential effect of vacuum annealing on the microstructure and hot salt corrosion behavior of CoNiCrAlY/YSZ/LaMgAl11O19 (LMA) double-ceramic coatings. A hot-salt corrosion test revealed that sprayed coatings exhibited an unsatisfactory anti-corrosion performance, and the LMA layer underwent severe fracture and corrosion degradation. Vacuum annealing induced a prominent recrystallization of the amorphous phase in LMA layer, triggering severe volume shrinkage and microcrack initiation. The recrystallization and volume shrinkage of the LMA layer were aggravated by an increase in the annealing temperature. The annealed coating with a higher fraction of the LaMA phase showed superior resistance to hot-salt corrosion. However, the salt mixture diffused simultaneously along the microcracks and eventually eroded into the YSZ layer. These results confirmed that vacuum annealing significantly enhanced the hot-salt corrosion resistance of the LMA layer. However, it deteriorated the barrier effect of the salt mixture through microcrack formation.

Highlights

In recent years, thermal barrier coatings (TBCs) have been widely used in the hot end components of aero-engines and gas turbines
Previous studies reported that since the LaMgAl11 O19 (LaMA) phases are covered by the amorphous phase, they are difficult to detect by XRD, resulting in low diffraction intensity [36,38]
The change in the diffraction strength of the LaMA peak was minor, but the area of the amorphous bulge decreased significantly, indicating that recrystallization occurred in the LaMgAl11 O19 (LMA) layer during vacuum annealing at 900 ◦ C

Summary

Introduction

Thermal barrier coatings (TBCs) have been widely used in the hot end components of aero-engines and gas turbines. The high oxygen conductivity of YSZ induces the formation of a thermally grown oxide between the YSZ and the bonding layer. This oxide can exacerbate the premature failure of the coating system [13,14,15,16]. YSZ coatings are unable to fulfill the growing need for the protection of hot end components during high-temperature service. It is essential to develop novel coating materials and structural designs for TBCs

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Conclusion