LC/8YSZ TBCs Thermal Cycling Life and Failure Mechanism under Extreme Temperature Gradients

Kun Liu,Xi Chen,Jinguang Du,Kangping Du,Yu Wang,Xinsheng Wang,Wuyi Ming

doi:10.3390/coatings11091051

Kun Liu, Xi Chen + Show 5 more

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https://doi.org/10.3390/coatings11091051

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Abstract

The purpose of this paper is to study the thermal shock resistance and failure mechanism of La2Ce2O7/8YSZ double-ceramic-layer thermal barrier coatings (LC/8YSZ DCL TBCs) under extreme temperature gradients. At high surface temperatures, thermal shock and infrared temperature measuring modules were used to determine the thermal cycling life and insulation temperature of LC/8YSZ DCL TBCs under extreme temperature gradients by an oxygen–acetylene gas flame testing machine. A viscoelastic model was used to obtain the stress law of solid phase sintering of a coating system using the finite element method. Results and Conclusion: (1) Thermal cycling life was affected by the surface temperature of LC/8YSZ DCL TBCs and decreased sharply with the increase of surface temperature. (2) The LC ceramic surface of the failure coating was sintered, and the higher the temperature, the faster the sintering process. (3) Accelerated life test results showed that high temperature thermal cycling life is not only related to thermal fatigue of ceramic layer, but is also related to the sintering degree of the coating. (4) Although the high temperature thermal stress had great influence on the coating, great sintering stress was produced with sintering of the LC ceramic layer, which is the main cause of LC/8YSZ DCL TBC failure. The above results indicate that for new TBC ceramic materials, especially those for engines above class F, their sinterability should be fully considered. Sintering affects the thermal shock properties at high temperature. Our research results can provide reference for material selection and high temperature performance research.

Highlights

With the increase of turbine temperatures of aero engines and gas turbines, the problem of high-temperature sintering of thermal barrier coatings becomes more and more serious [1,2]
Based on experimental observations of microstructure evolution of APS coatings during sintering [11,12,13], Siebert et al found that the formation of an interlaminar sintered neck would increase the Young’s modulus of the coating, and no phase change would occur in this process [14,15,16]
Surface morphology ofdetermine the thermal barrier coatin samples for Digital different photo surface temperatures were tested to their thermal cycling life

Summary

Introduction

With the increase of turbine temperatures of aero engines and gas turbines, the problem of high-temperature sintering of thermal barrier coatings becomes more and more serious [1,2]. Kumar and Cocks developed constitutive models involving elasticity, local contact, sintering, diffusion, and creep behavior On this basis, they further proposed a brick model to describe the microstructure evolution of coating sintering and predicted the influence of coating response and crack density on thermal conductivity under high temperature compression. Lv [9,28,29] found that there are often angles between lamella, presenting a wedge structure, which is not a traditional brick assumption in the model of parallel plate layer structures by an APS coating layer table interface topography evolution of experimental observation To this end, they established an APS coating microstructure model and wedge model considering a sintering neck and adopted an improved elasto-viscoplastic thermodynamic coupling constitutive model to discuss the influence of sintering neck formation on coating force and thermal behavior

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Conclusion