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The critical requirements for the environmental barrier coating (EBC) materials of silicon-based ceramic matrix composites (CMCs) include good tolerance to harsh environments, thermal expansion matches with the interlayer mullite, good high-temperature phase stability, and low thermal conductivity. Cuspidine-structured rare-earth aluminates RE4Al2O9 have been considered as candidates of EBCs for their superior mechanical and thermal properties, but the phase transition at high temperatures is a notable drawback of these materials. To suppress the phase transition and improve the phase stability, a novel cuspidine-structured rare-earth aluminate solid solution (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 was designed and successfully synthesized inspired by entropy stabilization effect of high-entropy ceramics (HECs). The as-synthesized HE (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 exhibits a close thermal expansion coefficient (6.96×10-6 K-1 at 300-1473 K) to that of mullite, good phase stability from 300 to 1473 K, and low thermal conductivity (1.50 W·m-1·K-1 at room temperature). In addition, strong anisotropic thermal expansion has been observed compared to Y4Al2O9 and Yb4Al2O9. The mechanism for low thermal conductivity is attributed to the lattice distortion and mass difference of the constituent atoms, and the anisotropic thermal expansion is due to the anisotropic chemical bonding enhanced by the large size rare-earth cations.


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High-entropy (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 with good high temperature stability, low thermal conductivity, and anisotropic thermal expansivity

Show Author's information Zifan ZHAOa,bHuimin XIANGaHeng CHENaFu-Zhi DAIaXiaohui WANGcZhijian PENGb( )Yanchun ZHOUa( )
Science and Technology on Advanced Functional Composite Laboratory, Aerospace Research Institute of Materials & Processing Technology, Beijing 100076, China
School of Engineering and Technology, China University of Geosciences, Beijing 100083, China
Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

Abstract

The critical requirements for the environmental barrier coating (EBC) materials of silicon-based ceramic matrix composites (CMCs) include good tolerance to harsh environments, thermal expansion matches with the interlayer mullite, good high-temperature phase stability, and low thermal conductivity. Cuspidine-structured rare-earth aluminates RE4Al2O9 have been considered as candidates of EBCs for their superior mechanical and thermal properties, but the phase transition at high temperatures is a notable drawback of these materials. To suppress the phase transition and improve the phase stability, a novel cuspidine-structured rare-earth aluminate solid solution (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 was designed and successfully synthesized inspired by entropy stabilization effect of high-entropy ceramics (HECs). The as-synthesized HE (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 exhibits a close thermal expansion coefficient (6.96×10-6 K-1 at 300-1473 K) to that of mullite, good phase stability from 300 to 1473 K, and low thermal conductivity (1.50 W·m-1·K-1 at room temperature). In addition, strong anisotropic thermal expansion has been observed compared to Y4Al2O9 and Yb4Al2O9. The mechanism for low thermal conductivity is attributed to the lattice distortion and mass difference of the constituent atoms, and the anisotropic thermal expansion is due to the anisotropic chemical bonding enhanced by the large size rare-earth cations.

Keywords:

(Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9, high-entropy ceramics (HECs), environmental barrier coatings, phase stability, thermal properties
Received: 23 May 2020 Revised: 15 June 2020 Accepted: 18 June 2020 Published: 10 October 2020 Issue date: October 2020
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Publication history
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Publication history

Received: 23 May 2020
Revised: 15 June 2020
Accepted: 18 June 2020
Published: 10 October 2020
Issue date: October 2020

Copyright

© The author(s) 2020

Acknowledgements

We acknowledge financial support from the National Natural Science Foundation of China (Grant Nos. 51672064 and 51972089).

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