Design of high-entropy rare-earth disilicate materials for thermal environmental barrier coatings through thermal-mechanical experiments and finite element simulation studies

Abstract

Multifunctional thermal environmental barrier coatings (TEBCs) with suitable thermal-mechanical properties and low thermal stresses are urgently needed to address the composite demands of thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) for silicon carbide ceramic matrix composites (SiC CMCs) structural components in aero-engines, while the development of high-entropy rare-earth disilicates provides a new opportunity. In this study, based on the doping weight values of different rare-earth elements and the periodic orthogonal incremental doping rules, 16 types of rare-earth disilicate ceramics were prepared by the solid-phase reaction method. The microstructures, thermal-mechanical properties, thermal mismatch stresses, and simulated thermal cycling stresses were investigated. A 4 × 4 thermal-mechanical periodic table for the prepared disilicates was creatively plotted and analyzed. When different rare-earth elements are doped in the Yb₂Si₂O₇ crystal structure, they lead to different changes in phase stability, thermal conductivity, thermal expansion coefficient, microhardness, Young's modulus, fracture toughness, and thermal stresses. However, among all the prepared disilicates, the high-entropy material (Sc_0.2Y_0.2Er_0.2Yb_0.2Lu_0.2)₂Si₂O₇ not only demonstrates lower thermal conductivity and a suitable thermal expansion coefficient, but also exhibits higher microhardness and Young's modulus, as well as reduced thermal cycling stress when applied as coatings, making it the most desirable candidate for TEBCs.