High entropy defective fluorite structured rare-earth niobates and tantalates for thermal barrier applications

Zifan Zhao,Kuang Sun,Heng Chen,Fu-Zhi Dai,Xiaohui Wang,Huimin Xiang,Zhijian Peng,Wei Xu,Yanchun Zhou

doi:10.1007/s40145-020-0368-7

Abstract

Rare-earth tantalates and niobates (RE3TaO7 and RE3NbO7) have been considered as promising candidate thermal barrier coating (TBC) materials in next generation gas-turbine engines due to their ultra-low thermal conductivity and better thermal stability than yttria-stabilized zirconia (YSZ). However, the low Vickers hardness and toughness are the main shortcomings of RE3TaO7 and RE3NbO7 that limit their applications as TBC materials. To increase the hardness, high entropy (Y1/3Yb1/3Er1/3)3TaO7, (Y1/3Yb1/3Er1/3)3NbO7, and (Sm1/6Eu1/6Y1/6Yb1/6Lu1/6Er1/6)3(Nb1/2Ta1/2)O7 are designed and synthesized in this study. These high entropy ceramics exhibit high Vickers hardness (10.9–12.0 GPa), close thermal expansion coefficients to that of single-principal-component RE3TaO7 and RE3NbO7 (7.9×10−6-10.8×10−6C−1 at room temperature), good phase stability, and good chemical compatibility with thermally grown Al2O3, which make them promising for applications as candidate TBC materials.

Highlights

Thermal barrier coatings (TBCs) have widely been used in the gas-turbine engines to improve the energy efficiency and protect the hot structure components from foreign particle impact, water vapor, and moltenCurrently, the state-of-the-art thermal barrier coating (TBC) material is yttria-stabilized zirconia (YSZ) due to its outstanding mechanical and thermal properties, such as high strength www.springer.com/journal/40145J Adv Ceram 2020, 9(3): 303–311 and toughness, high melting point, close thermal expansion coefficient to that of metal substrate, and low thermal conductivity [10,11,12]
Due to the combination of many intriguing properties, such as good thermal stability, large thermal expansion coefficients, simple crystal structure but extremely low thermal conductivity, RE3TaO7 and RE3NbO7 have been considered as promising TBC materials for higher temperature applications [16,17]
The high hardness, better phase stability, and good chemical compatibility with Al2O3 indicate that these new types of high entropy ceramics (HECs) are promising as high-performance TBC materials

Summary

Introduction

Thermal barrier coatings (TBCs) have widely been used in the gas-turbine engines to improve the energy efficiency and protect the hot structure components from foreign particle impact, water vapor, and molten. Due to the combination of many intriguing properties, such as good thermal stability, large thermal expansion coefficients, simple crystal structure but extremely low thermal conductivity, RE3TaO7 and RE3NbO7 have been considered as promising TBC materials for higher temperature applications [16,17]. Previous studies indicate that the mechanical properties of RE3TaO7 and RE3NbO7, such as Vickers hardness, are significantly lower than those of YSZ [17,22,23,24] Some compounds such as Sm3TaO7 and Sm3NbO7 exhibit phase transition with an abrupt volume change at 942 and 817 °C, respectively, which is unfavorable to their application as TBC materials [22,25]. The high hardness, better phase stability, and good chemical compatibility with Al2O3 indicate that these new types of HECs are promising as high-performance TBC materials

Experimental

Results and discussion

Conclusions