Preparation, thermophysical properties and corrosion resistance of high-entropy rare earth tantalates (5RE0.2)TaO4 (RE=Y, Gd, Dy, Ce, Sm, La, Yb) ceramics as promising thermal barrier coating materials

With the development of high power and high thrust-weight ratio aeronautics and astronautics, aircraft engines and gas turbine technology, the development of thermal barrier coating (TBCs) material is an enormous challenge, which requires both high temperature stability and resistance to molten calcium-magnesium-aluminosilicate (CMAS) corrosion. In this study, five high-entropy rare-earth tantalate (5RE 0.2 )TaO 4 (Re=Y, Gd, Dy, Ce, Sm, La, Yb) ceramics were prepared by high temperature solid state reaction. The phase composition, microstructure, thermophysical and mechanical properties and CMAS corrosion resistance of the obtained high-entropy (5RE 0.2 )TaO 4 ceramics were systematically investigated. The as-prepared five high-entropy rare-earth tantalate (5RE 0.2 )TaO 4 ceramics had monoclinic structure and uniform composition. The five (5RE 0.2 )TaO 4 ceramics all had lower Young’s modulus (135.06∼158.63 GPa), Vickers hardness (3.7∼6.2 GPa), fracture toughness (2.30-2.80 MPa·m 1/2 ) and brittleness index (1.45-2.53 μm –1/2 ) than that of YSZ. The thermal expansion rate and thermal expansion coefficients of the five (5RE 0.2 )TaO 4 ceramics were close to each other but showed higher value than that of single RETaO 4 (RE= Gd, Dy, Sm or Y) and lower value than that of YSZ. The thermal diffusivities and thermal conductivity of the five (5RE 0.2 )TaO 4 ceramics were lower than that of YSZ, YTaO 4 and GdTaO 4 at all temperature. During molten CMAS corrosion, CMAS melt diffused into the (5RE 0.2 )TaO 4 ceramics and then corroded (5RE 0.2 )TaO 4 grains, thereby forming a corrosion area composed of reaction layer and penetration layer. The CaO in penetrated CMAS melt could react with Ta element in (5RE 0.2 )TaO 4 ceramics to generate Ca 2 Ta 2 O 7 in the reaction layer and reduce the content of CaO in the penetrated CMAS melt, which increased the viscosity of the CMAS melt and inhibited the further penetration of CMAS into the ceramics. Based on the obtained results, the CMAS corrosion of (5RE 0.2 )TaO 4 ceramics was primarily controlled by the Ca 2 Ta 2 O 7 formation and the CMAS penetration.