Thermophysical Property of Single-phase Strontium Zirconate Co-doped with Double Rare-earth Oxides as a Thermal Barrier Coating Material

doi:10.15541/jim20180276

Abstract

Abstract:

Due to the different vapor pressures between SrO and ZrO₂, composition of air plasma sprayed (APS) SrZrO₃ coating deviates from stoichiometric SrZrO₃, resulting in formation of second phase ZrO₂ in the as-sprayed SrZrO₃ coating. To obtain single-phase coating with high phase stability, the Sr_1.1(Zr_0.9Yb_0.05Gd_0.05)O_3.05 powder with excess Sr was synthesized by solid state reaction and spray drying, followed by air plasma spray to obtain the Sr_1.1(Zr_0.9Yb_0.05Gd_0.05)O_3.05 coating. Thermo-physical properties and thermal cycling behavior of the Sr_1.1(Zr_0.9Yb_0.05Gd_0.05)O_3.05 coating were investigated. Experimental results showed that the Sr_1.1(Zr_0.9Yb_0.05Gd_0.05)O_3.05 coating had no second phase and showed a good high-temperature phase stability after heat- treatment at 1600 ℃ for 360 h. The sintering rate of the as-sprayed Sr_1.1(Zr_0.9Yb_0.05Gd_0.05)O_3.05 coating was 7.27×10 ^-6 s ^-1. Thermal expansion coefficients (TECs) and thermal conductivity of the coating after heat-treatment at 1600 ℃ for 360 h were (9.0-11.0)×10 ^-6 K ^-1 (200-1400 ℃) and 2.83 W/(m?K) (1000 ℃), respectively. Thermal cycling lifetime of the Sr_1.1(Zr_0.9Yb_0.05Gd_0.05)O_3.05/YSZ double ceramic layer coating was 1000 cycles, due to failure occurring in the Sr_1.1(Zr_0.9Yb_0.05Gd_0.05)O_3.05 coating. Moreover, singe-phase Sr_1.1(Zr_0.9Yb_0.05Gd_0.05)O_3.05 coating with SrZrO₃structure could be prepared by adding excess SrO in the feedstock, which showed higher TEC by co-dopping with Yb₂O₃ and Gd₂O₃ and sintering resistance than did the SrZrO₃ coating. However, the thermal conductivity of the Sr_1.1(Zr_0.9Yb_0.05Gd_0.05)O_3.05 coating is higher than that of the SrZrO₃ coating because of the absence of the second phase.

Key words: thermal barrier coating, SrZrO₃, thermal expansion, thermal conductivity

CLC Number:

TQ174

Bo-Le MA, Wen MA, Wei HUANG, Yu BAI, Rui-Ling JIA, Hong-Ying DONG. Thermophysical Property of Single-phase Strontium Zirconate Co-doped with Double Rare-earth Oxides as a Thermal Barrier Coating Material[J]. Journal of Inorganic Materials, 2019, 34(4): 394-400.

Figures/Tables 9

Fig. 1 SEM images of two different powders

Table 1 Parameters of spraying

Current/A	Ar/(L?min^-1)	H₂/(L?min^-1)	Spray distance/mm	Power/kW
500	40	10	100	35.8

Fig. 2 XRD patterns of powders and coatings after heat-treatment at 1600 ℃ for different time

Fig. 3 TECs of two different coatings after heat-treatment at 1600 ℃ for different time

Fig. 4 Sintering shrinkage kinetics of two different free- standing coatings

Fig. 5 Thermal diffusivities of two different coatings after heat-treatment at 1600 ℃ for different time

Fig. 6 Densities of two different coatings

Fig. 7 Thermal conductivities of two different coatings after heat-treatment at 1600 ℃ for different time

Fig. 8 Photographs (a-b) and SEM microstructures (c-d) of coatings after burner rig tests (a, c) Sr1.1(Zr0.9Yb0.05Gd0.05)O3.05; (b, d) Sr1.1(Zr0.9Yb0.05Gd0.05)O3.05/YSZ

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