Computational Design of High-Entropy Rare Earth Disilicates as Next-Generation Thermal/Environmental Barrier Coatings

Abstract

Development of advanced thermal/environmental barrier coating (T/EBC) materials possessing balanced thermal-mechanical properties is crucial to protect SiC-based ceramic composites from chemical and thermal attack for better performance of components in the hot section of gas turbine engines. In this work we utilize density functional theory (DFT) together with combinatorial chemistry methodology to design high-performance high-entropy rare earth disilicates (β-RE2Si2O7 (RE=Yb, Y, Er, Lu, La, Ce,)) for enhanced phase stability, desired coefficient of thermal expansion (CTE), low lattice thermal conductivity and good mechanical properties. The CTE are determined by phonon calculations at different volumes within the quasi-harmonic approximation. The lattice thermal conductivities are evaluated by the Debye-Callaway model considering three phonon processes. We show that the solid solution of YYbSi2O7 exhibits lowered lattice thermal conductivity than pure cases and a good range of CTE. We also present good EBC candidate materials of Er1/4Lu1/4Y3/4Yb3/4Si2O7 and Er1/2Lu1/2Y1/2Yb1/2Si2O7 with very low lattice thermal conductivity < 0.23 W/m/K at 1500 K and a good match of average CTE (5.1 - 5.2×10−6 K−1) with SiC without compromising mechanical properties. These new EBC with outstanding multi-functional properties are believed to enable significant increases in the performance of protective components in gas turbines. This work also illustrates an efficient and reliable computational framework in accelerating the design of next-generation T/EBC.