High-Temperature CMAS Corrosion of Multicomponent Equimolar Rare-Earth Zirconates (Y0.2Nd0.2Sm0.2Gd0.2Dy0.2)2Zr2O7 and (Nd0.2Sm0.2Gd0.2Dy0.2Er0.2)2Zr2O7

Corrosion resistance experiments of the two high-entropy rare-earth zirconates (Y 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Dy 0.2 ) 2 Zr 2 O 7 and (Nd 0.2 Sm 0.2 Gd 0.2 Dy 0.2 Er 0.2 ) 2 Zr 2 O 7 against calcium-(magnesium)-aluminosilicates (C(M)AS) at 1300 °C were performed to simulate interactions of siliceous debris with thermal barrier coatings in aircraft applications. The high-entropy approach is used for phase stabilization and minimization of thermal conductivity for the materials’ application, thus the behavior of the different lanthanide cations during the corrosion and their incorporation in product phases is under investigation. Model compositions of C 24 A 17 S 59 and C 33 M 9 A 13 S 45 were used to determine the influence of basicity on the corrosion behavior. The investigations, which are compared to single-component Gd 2 Zr 2 O 7 and which cover a wide range from short to long-term corrosion tests, show the reaction progress and phase formation of rare-earth-calcium-silicates in apatite structure, as well as the formation of zirconia and/or zircon. Investigations of the elemental composition of the different phases show lanthanide gradients in the product phases depending on their cationic radii.