Effect of configurational entropy on the mechanical and thermal properties of rare earth aluminates-rare earth zirconates composite

Abstract

To improve the working temperature of gas turbines, thermal barrier coatings (TBCs) to replace the meta-stable Y₂O₃ partially stabilized ZrO₂ have been explored for decades. Rare earth zirconates (RE₂Zr₂O₇) are regarded as an excellent candidate for next-generation thermal barrier coatings. However, the low fracture toughness of rare earth zirconates is the main hindrance, while the rare earth aluminates (REAlO₃) can be imported into the system to toughen the zirconates. In this work, we introduced multiple rare earth elements to explore the effects of configurational entropy on the mechanical and thermal properties of REAlO₃-RE₂Zr₂O₇ composites. When the high entropy REAlO₃-RE₂Zr₂O₇ composites with 3, 4, and 5 rare earth elements on A site were successfully synthesized, the phases of zirconates and aluminates were kept and the rare earth elements were distributed uniformly. We found that the increase in configurational entropy profoundly improved the fracture toughness of the composites by the entropy effect. The fracture toughness of HE-RAO-RZO-5 reached 3.81 ± 0.66 MPam^1/2 measured by the single-edge notched beam (SENB) method, exceeding the fracture toughness given by the mixing rule by ∼18%, which is among the best values of new TBC materials. Meanwhile, the coefficient of thermal expansion can be tuned by the compositions and the hardness, Young's modulus and thermal conductivity of the composites remained almost unchanged. As a result, we proved that the introduction of configurational entropy could be an excellent method to improve the fracture toughness and tailor the thermal properties of REAlO₃-RE₂Zr₂O₇ composites.